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ASYNCHRONOUS FUNCTIONS FOR MICROSOFT, TURBO, OR ZORTECH C The LIB(s) on the included disk are libraries of serial communications functions designed specifically for use with Microsoft C, Turbo C / C++, and Zortech C / C++. The regis- tered version has LIBs for all memory models. The shareware version is small model only. --- Features of the library functions --- o Support for 16550 UART's FIFO mode of operation o Fully interrupt driven o Baud rates up to 115,200 baud o User defined transmit and receive ring buffer sizes. o Ring buffers may be in placed in FAR memory even in small and medium model programs. o User defined port addresses, IRQ use, and interrupt vector numbers. o Support for simultaneous operation of 2 ports. o Built in support for XON/XOFF and hardware flow control o Block transmit and receive functions o Receive buffer look ahead function o 100% assembler code for maximum speed o Totally compatible with Microsoft C, Turbo C, Zortech C, and other C compilers that use standard Microsoft high level language calling conventions. --------------------------------------------------------------- Mike Dumdei, 6 Holly Lane, Texarkana TX 75503 MCOMM5 (c) 1989, 1990, 1991 All Rights Reserved --------------------------------------------------------------- REGISTRATION AND DISTRIBUTION POLICY MCOMM5, the various versions of Smalterm, the ANSI video routines, and other miscellaneous functions contained in the COMM_x libraries are distributed as shareware. If you use these functions regularly please register them. Two types of registration are available for MCOMM5. The first is $25 and includes assembled libraries for all memory models. The $25 registration does not include source code. The second type of registration is $45 and includes libraries and source code. Previous versions were $25 for source code and libraries. If you send $25 and want source code based on previous offers, you will receive a previous version of the source. Registered users of versions prior to version 5 may upgrade their libraries for $3 or upgrade source code version for $10. Considerable time and effort has gone into developing and debugging these routines. If you are not a registered user and have obtained a copy of the registered version, please take time now to register the software or delete it. The copy you have is a registered version if it contains libraries for any memory model other than small model or if any of the ASM source code is included. This software is provided as is without warranty as to its fitness for a particular use or being free of errors. I assume no liability for any loss or damages you may incur through its use. I will, however, make every effort to correct any software errors that may exist, and provide you with a working version. I will continue to assist registered and non-registered users whenever possible. If you have any problems using these routines or questions, I may be contacted at: North East Texas DataLink -- 903 838-6713 (modem) FIDO net: 1:19/128 Mike Dumdei -- 903 838-8307 (voice) GETTING STARTED All functions included in this library are listed on the fol- lowing pages in alphabetical order. The basic functions needed to begin are: async_open, async_tx, async_rx, and async_close. Functions are also available to support XON/XOFF and hardware flow control, the 16550 UART, block transmit and receive, receive buffer look ahead, and several other features. All functions take a pointer to an ASYNC structure for one of its arguments. This structure is defined in COMM.H. It may be helpful to think of this structure as being similar to the standard C library 'FILE *'. If you have been using versions of these routines prior to version 5.00, there have been some changes made that will require you to make some modifications to any existing code before it can be used with the new libraries. The main differences are: > Async_open takes different parameters. Also, instead of the open function automatically allocating the ring buffers for you, you provide the ring buffers. > All functions now take a pointer to an ASYNC structure as the first argument rather than 0 (COM1) or 1 (COM2). > LITES is no longer supported. NOTES ON 16550 FIFO MODE The 16550 UART is automatically detected and enabled when async_open is called. If, for some reason, you want to operate a 16550 UART in non-FIFO mode, automatic detection and use can be disabled. See async_open for more information. --- Use of receiver FIFOs --- The receiver trigger level may be programmed for 1, 4, 8, or 14 bytes by the async_FIFOrxlvl function. When a port is first opened the trigger is set to 1 byte. There are 3 reasons why I chose to default to a 1 byte receive trigger level. 1) While a higher trigger level results in less CPU overhead, it also provides less overrun protection if the CPU is slow to respond. For example, with a 1 byte trigger level the 16550 -- when it generates an interrupt -- can hold 15 more characters in its FIFOs before the CPU responds. With a 14 byte trigger level it will only have room for 2 more characters. 2) The MCOMM interrupt functions completely empty the receiver FIFOs every time an interrupt occurs. If the CPU is slow to respond, the interrupt handler will process 2,3,4.. characters (whatever is in the FIFOs) whenever it does get control so the data still gets buffered if the CPU isn't able to keep up. 3) Setting the trigger level at higher trigger levels when displaying incoming data to the screen will result in a jerky looking display, especially at low baud rates. Again, this is because MCOMM empties the buffer completely when it processes the interrupt. With a trigger level other than 1, data stacks up in the FIFOs until the trigger level is reached. When the interrupt finally occurs, all the data in the FIFOs is pulled out and made available to the higher level functions at one time. The result is your code sits for 4, 8, or 14 bytes (whatever the trigger is) and then puts those bytes on the screen in a burst. It looks rough at low baud rates. At 9600 baud and above you could probably get by with a slightly higher trigger level. For best use of the receive FIFOs, stick with 1 byte trigger level when displaying data to the screen. If your application does not display the data or uses a high baud rate, you may want to experiment with setting it to either 4 or 8 bytes. --- Use of transmit FIFOs --- The MCOMM transmit interrupt handler takes a parameter (set by async_FIFOtxlvl) that is the maximum number of bytes to load into the transmit FIFOs at one time. The default value for NOTES ON 16550 FIFO MODE this parameter is 3 bytes. The reason for not loading up the FIFOs to maximum capacity (16 bytes) is flow control. The 16550 UART will continue to transmit characters in its FIFOs regardless of the state of CTS, DSR, or CD, or if an XOFF is received. It is totally up to the software to respond to requests for flow control. If the FIFOs are loaded with more bytes than the receiver can handle when it invokes flow control, the receiver gets overwritten. There is a bit that can be sent to the UART to flush the transmit FIFOs but then it is impossible to tell what was flushed and what was sent. The solution is to not the load the FIFOs up so full. If the receiving device can handle more than 3 characters of overrun, use a larger value. If the application does not require flow control, you can use a 16 byte level with no problems. Another factor to consider concerning the transmit FIFO byte level is that (from the NS Data Communications/LAN/UART Handbook) the transmit FIFO empty indication will be delayed by 1 character time minus the last stop bit until there are at least 2 bytes in the transmit FIFOs simultaneously for the current transmit operation. After the 2 byte requirement is met the transmit interrupt occurs immediately when the transmit FIFOs empty. Using a value of 3 or above (1 byte for the transmit shift register and 2 for the FIFO registers) guarantees the interrupt delay is deactivated. Once the '2 bytes in the FIFOs' requirement is met, the transmit byte level can be reduced if necessary. --- Problems with Western Digital 16550s --- The following problems DO NOT apply to the National Semicon- ductor version of the 16550. Neither are they unique to MCOMM. Western Digital 16550 UARTs have two problems you should be aware of if your application will be ran on system that uses this chip. The first of these only shows up under the following conditions: 1) The UART is in FIFO mode. 2) A low baud rate is being used. 3) The transmitter is initially empty. 4) A block of data longer than 16 to 18 bytes (depth of the FIFOs plus 1 or 2 for what gets out while the FIFOs are being filled up) is sent to the chip. Under these conditions the WD16550 UART will momentarily fail to recognize the FIFOs are full and continue to generate transmit interrupts. It also fails to reset the 'Transmit Hold Register Empty' bit making it impossible for the software to detect a full FIFO condition. The result is the software keeps sending data to the chip, overrunning the FIFOs. What you will NOTES ON 16550 FIFO MODE see is, the first 16 to 18 bytes transmitted correctly, a missing block of data, and then the remainder of the block also correct. This can be verified by trying to send blocks of data through this chip (WD16550) at a low baud rate with any software that enables the FIFOs. How low of a baud rate is low enough to cause the problem depends on the particular chip and how fast the CPU and software can supply data to the chip. With MCOMM, a 20 MHZ 386, and the TxByteCnt at the default level of 3, the chip I was testing would not work in FIFO mode below 9600 baud. On the same system using different software, it worked as low as 4800 baud. On a 12 MHZ 286, MCOMM would work at 4800 and above while the other software worked at 2400 and above. For publicly distributed applications, I recommend you do one or more of the following: 1) Provide an option in your program to allow the end user to operate a 16550 with the FIFOs disabled. When the FIFOs are disabled, all baud rates work. ORing the ComBase parameter of async_open with 0x4000 will force FIFO mode off. 2) Provide an option in your program to allow setting the TxByteCnt level (async_FIFOtxlvl) to a lower value. This will help slightly. 3) Put a flag in your program the end user can set to let you know you are dealing with a WD16550. 4) State your application does not support the Western Digital version of the 16550 at low baud rates. The second problem with the WD16550 is that if the 'Clear to Send' signal is not connected it can, under some conditions, cause the 'Delta Clear to Send' bit in the Modem Status Register to become set and it will not reset. I did not research the problem enough to know if the 'locked bit' only occurs when MSR interrupts are enabled, whether other floating MSR input signals can cause the same problem, if all WD16550's have the problem, or that is unique to the Western Digital chip (considering the FIFO overrun problem, I assume it is unique). With a properly functioning UART, reading the MSR register will reset all the 'delta bits' and clear any interrupts. With the chip I had, I tried everything I could think of to clear the interrupt and nothing worked except the ON/OFF switch. I tried clearing interrupts and reading the MSR multiple times checking to see if the bit reset with interrupts off (it didn't), disabling Modem Status interrupts via the Interrupt Enable Register and then reading the MSR register (didn't work), FIFO mode on / FIFO mode off (no difference), keyboard reboot of the computer (didn't fix it), shut the computer off and turn it back on (that fixed it). NOTES ON 16550 FIFO MODE After encountering this problem and having the system lock up, I added code to MCOMM's interrupt driver so that it would quit trying to clear an interrupt after 1000 attempts. It then sets a new port structure member 'IERVal' to zero as an indicator the port is locked up. Normally 'IERVal' will be set to the current value of the Interrupt Enable Register. If you try to open a port that is in a stuck interrupt condition, async_open now returns R_UARTERR. In addition, options were added to open a port without enabling Modem Status interrupts or Line Status interrupts or both. ORing the ComBase parameter of async_open with 0x2000 disables MSR interrupts. ORing with 0x1000 disables LSR interrupts. So far I have encountered no reason for disabling LSR interrupts. Disabling MSR interrupts prevents the lock up problem but has the side effect of causing all functions and variables that use Modem Status signals to be invalid. This includes hardware handshake and carrier detect. I have probably over emphasized the Modem Status lock up problem and my personal opinion is that it is not that serious. I considered totally disregarding it since it has a simple solution and that is to connect all Modem Status input signals to some driving signal (wire the RS232 cable right). Unused signals can be connected to a driving signal on the computer end if necessary. Also it may be isolated to one defective chip. I tested two WD16550s and the problem only showed up on one of them during my testing. Because the computer totally locked up when this happened though, I decided to go ahead and program for the possibility. At least control of the computer is regained and you can tell the user he needs a properly wired RS232 cable or his UART is broke and then exit gracefully. This will probably show up very very rarely so don't be too concerned about it. In closing, I would like to point out again that these problems are a fault of the WD16550 and are not unique to MCOMM. async_16550 --------------------------------------------------------------- Purpose: Check if 16550 UART was detected in system. Format: int async_16550(port); ASYNC *port; Pointer to ASYNC structure Example: ASYNC *port; int is_16550; is_16550 = async_16550(port); Returns: Returns zero if a 16550 is not in the system or the 'ignore 16550 bit' was set when async_open was called. Returns NZ if a 16550 was found. Async_open must be called before this function is valid. If a 16550 is found, it will be placed in the FIFO mode of operation by async_open unless '16550 detect' was overridden or the force FIFOs off option was selected. Remarks: This function is implemented as a macro. See async_open. async_breakrxd --------------------------------------------------------------- Purpose: Checks if a break signal has been received. Format: int async_breakrxd(port); ASYNC *port; Pointer to ASYNC structure Example: ASYNC *port; int break_status; break_status = async_breakrxd(port); Returns: If a break signal has been received the function returns a non-zero value. If a break has not been detected, zero is returned. Remarks: Once a break signal has been detected, this function continually returns non-zero values until async_reset is called. If a break is received, a line status register interrupt is generated. The interrupt handler sets a bit in the Stat1 port structure member. The async_breakrxd function is a macro that checks the status of this bit. See also async_reset, async_rx, async_stat, async_sndbrk. async_carrier --------------------------------------------------------------- Purpose: Check for the presence of a carrier. Format: int async_carrier(port); ASYNC *port; Pointer to ASYNC structure Example: ASYNC *port; int carrier_status; carrier_status = async_carrier(port); Returns: A non-zero value is returned if a carrier is present. If the carrier detect line is LOW, zero is returned. Remarks: This function is implemented as a macro. See also async_rx and async_stat. async_close --------------------------------------------------------------- Purpose: Closes a port opened by async_open. Format: int async_close(port); ASYNC *port; Pointer to ASYNC structure Example: ASYNC port; async_close(&port); Returns: No return value Remarks: Do not attempt to close an unopened port. Some minimal checking is done internally by async_close in an attempt to detect whether or not the specified port is actually opened. If an unopened port makes it past those checks and the main close routine is entered, the system may lock up (immediately, 2 hours later, or never). When a port is closed the UART registers, interrupt controller mask, and interrupt vectors are restored to the value they had when async_open was called. It is possible to close the port and leave various signals (DTR for one) in the state you desire rather than in their initial state. See async_dtr and async_rts for some examples on how to do this. The B_ORGFIFO bit in the ASYNC 'Stat3' structure member is used by async_close to return the 16550 -- if present -- to the mode it was in when async_open was called. FIFOs may be 'forced' to remain enabled or 'forced' to be disabled when closing the port by first setting or resetting this bit. Ex: Force off: port->Stat3 &= ~B_ORGFIFO; async_close(port); Force on: port->Stat3 |= B_ORGFIFO; async_close(port); async_cts --------------------------------------------------------------- Purpose: Check status of the Clear to Send signal. Format: int async_cts(port); ASYNC *port; Pointer to ASYNC structure Example: ASYNC *port; int cts_status; cts_status = async_cts(port); Returns: Returns zero if Clear To Send is LOW. If CTS is HIGH, a non-zero value is returned. Remarks: This function is implemented as a macro. async_dsr --------------------------------------------------------------- Purpose: Check status of the Data Set Ready signal. Format: int async_dsr(port); ASYNC *port; Pointer to ASYNC structure Example: ASYNC *port; int dsr_status; dsr_status = async_dsr(port); Returns: Returns zero if Data Set Ready is LOW. If DSR is HIGH, a non-zero value is returned. Remarks: This function is implemented as a macro. async_dtr --------------------------------------------------------------- Purpose: Set or reset the Data Terminal Ready signal. Format: void async_dtr(port, DTRflag); ASYNC *port; Pointer to ASYNC structure int DTRflag; Set/Reset DTR flag Example: ASYNC *port; if (WantToDropDTR) async_dtr(port, 0); else if (WantDTRhigh) async_dtr(port, 1); Returns: No return value Remarks: This signal is set HIGH when a port is first opened. When the port is closed, it is restored to the cond- ition it was in when the port was opened. To force DTR low when a port is closed, regardless of its state when the port was opened, AND the port member, OldMCR, with NOT B_DTR. To force DTR to remain high when the port is closed, OR OldMCR with B_DTR. Force low: port->OldMCR &= ~B_DTR; async_close(port); Force high: port->OldMCR |= B_DTR; async_close(port); async_FIFOrxlvl <5.20 addition> --------------------------------------------------------------- Purpose: Set the 16550 UART's receive trigger level. Format: void async_FIFOrxlvl(port, trigger_lvl); ASYNC *port; Pointer to ASYNC structure int trigger_lvl; Rx FIFO interrupt trigger level Example: ASYNC *port; /* set the receiver trigger level to 8 bytes */ async_FIFOrxlvl(port, 8); Returns: No return value Remarks: Valid values for 'trigger_lvl' are 1, 4, 8, and 14 bytes. When a port with a 16550 UART is first opened, the trigger level is set to 1 byte. See the discussion on 'Use of receiver FIFOs' at the beginning of this document. This function has no effect if the FIFOs were not enabled when async_open was called. async_FIFOtxlvl <5.20 addition> --------------------------------------------------------------- Purpose: Set the number of bytes loaded into the 16550 UART's transmit FIFOs when a transmit interrupt occurs. Format: void async_FIFOtxlvl(port, bytes); ASYNC *port; Pointer to ASYNC structure int bytes; # of bytes to load into tx FIFOs Example: ASYNC *port; /* set the transmit FIFO byte level to 16 bytes */ async_FIFOrxlvl(port, 16); Returns: No return value Remarks: Valid values for 'bytes' are 1 through 16 bytes. When a port with a 16550 UART is first opened, the transmit level byte count is set to 3 bytes. See the discussion on 'Use of transmit FIFOs' at the beginning of this document. This function has no effect if the FIFOs were not enabled when async_open was called. async_ignerr --------------------------------------------------------------- Purpose: Set or reset 'ignore characters with errors' bit Format: void async_ignerr(port, flag); ASYNC *port; Pointer to ASYNC structure int flag; Set/Reset flag Example: ASYNC *port; if (WantToDiscardErrChars) async_ignerr(port, 1); else if (WantToKeepErrChars) async_ignerr(port, 0); Returns: No return value Remarks: This function sets the bit that determines what hap- pens to received characters that have parity or fram- ing errors. If the function is called with the flag set to one, incoming characters that have framing or parity errors are discarded -- they do not get put into the receive ring buffer. If the flag is 0, char- acters with errors are not ignored, they are put into the ring buffer. The error bits in Stat1 that reflect these error conditions are set regardless of the setting of the discard flag. When a port is first opened, the flag is set to 0. This function is imple- mented as a macro. See also async_stat. async_msr --------------------------------------------------------------- Purpose: Get the contents of the Modem Status Register. Format: int async_msr(port); ASYNC *port; Pointer to ASYNC structure Example: ASYNC *port; int MSRcontents; MSRcontents = async_msr(port); Returns: The contents of the Modem Status Register. Remarks: This function is a macro that returns the port struc- ture member, MSRVal. This value is initialized when a port is first opened and then updated any time a modem status interrupt occurs. The reason the MSR is not read directly is to avoid inadvertently intercepting a pending MSR interrupt. All bits returned except for the delta bits reflect the true current status. async_msrflow <5.50 modified> --------------------------------------------------------------- Purpose: Enables or disables hardware flow control. Format: void async_msrflow(port, flowmask); ASYNC *port; Pointer to ASYNC structure int flowmask; Bit mapped flow control mask Example: ASYNC *port; if (enable_RTS_CTS_handshake) async_msrflow(port, B_CTS); else if (disable_handshake) async_msrflow(port, 0); Returns: No return value Remarks: The flow mask is a bit mapped value of the signal that is monitored by the receiver when performing flow control. Bits that may be monitored are B_CTS, B_DSR, and B_CD. This provides capability for RTS/CTS hand- shake, DTR/DSR handshake, and handshaking with the carrier detect line. To monitor multiple signals, OR the bits together. Both hardware flow control and XON/XOFF flow control may be enabled at the same time. Beginning with version 5.50, ORing B_RTS into the 'flowmask' parameter, will cause the RTS signal to be driven low whenever the receive buffer exceeds the XoffTrip point. RTS will automatically return to its normal condition when the receive buffer empties to a point below the XonTrip level. Both XOFF/XON and RTS flow control share the same trip point variable but may be activated separately or together. Do not get RTS and CTS confused. Use CTS to keep the computer from overrunning a device (e.g. sending to a modem with a locked baud rate). Use RTS to keep from getting ran over by a device (receiving from a high speed modem using a slow computer). See async_xflow. async_open <5.40 modified -- see Remarks at end of function> --------------------------------------------------------------- Purpose: Initializes the hardware, interrupt vector, and ASYNC port structure for interrupt driven operation. Format: int async_open(port, base, irqmask, vctrnbr, params); ASYNC *port; Pointer to ASYNC structure int base; Base port address of UART chip int irqmask; 8259 mask value for selected IRQ line int vctrnbr; Number of selected interrupt vector char *params; Baud, parity, data, & stop bits in string format Entry: Before calling this function you must allocate ring buffer memory and pre-initialize the following ASYNC structure members: RxSize : the size that you want the receive ring buffer to be. The memory allocated or set aside for the receive ring buffer must be contiguous with the memory used for the transmit ring buffer. In most cases (RxSize + TxSize) bytes will be allocated using some form of malloc. A function to do this is included in the examples. The combined size of RxSize + TxSize can not exceed 32K - 1. TxSize : the size of the transmit buffer in bytes. As stated above, the transmit and receive buffers for each individual port must be allocated as one contiguous block. RingSeg: the segment address of the memory allocated for the receive and transmit buffers. FAR memory can be used for the receive and transmit buffers by using your compiler library's version of FAR malloc and putting the segment portion (high 16 bits) of the returned memory pointer in RingSeg. If you are using a NEAR data model program and want NEAR ring buffers, set RingSeg equal to 0. With RingSeg set to zero, the open function will use the DS segment register for RingSeg. Using FAR ring buffers causes no loss of performance. RingOfst: the offset address of the memory allocated for the receive and transmit buffers. This value, in conjunction with the RxSize and TxSize vari- ables, is used to set up the receive and transmit ring buffers. async_open --------------------------------------------------------------- THE FOLLOWING FUNCTION IS INCLUDED WITH MCOMM5 AND IS RECOMMENDED FOR ALLOCATING RING BUFFER MEMORY AND INITIALIZING THE ABOVE VARIABLES. #if defined (__TURBOC__) /* Turbo C */ #include <alloc.h> #define _fmalloc farmalloc #elif defined (__ZTC__) /* Zortech C */ #include <dos.h> #include <stdlib.h> #define _fmalloc farmalloc #else /* Microsoft C */ #include <malloc.h> #endif int AllocRingBuffer( ASYNC *port, /* pointer to port structure */ int rxsize, /* number bytes to use for receive buffer */ int txsize, /* number bytes to use for transmit buffer */ int useFARmem) /* flag set if using FAR mem for buffers */ { unsigned long memptr; int memsize; memsize = rxsize + txsize; if (useFARmem || sizeof(char *) == 4)/* if FAR Ring bufs */ memptr = (unsigned long)_fmalloc(memsize); else /* if Ring buffers use NEAR memory */ memptr = (unsigned long)(unsigned int)malloc(memsize); /* pre-initialize 4 required structure members */ port->RxSize = rxsize; /* receive buffer size */ port->TxSize = txsize; /* transmit buffer size */ port->RingSeg = (int)(memptr >> 16); /* SEG adr */ port->RingOfst = (int)memptr; /* OFST address */ if (memptr == 0L) return 0; /* return 0 if no memory available */ return 1; /* return 1, had some memory */ } async_open --------------------------------------------------------------- Example 1: /* Open COM1 at 2400,N,8,1 using FAR ring buffers. COM1 is defined in COMM.H as: 0x3f8, 0x10, 12. It is not necessary to check the return value of AllocRingBuffer since async_open will return R_NOMEM if the memory allocation function fails. */ #include "comm.h" ASYNC port; int rcode; AllocRingBuffer(&port, 24000, 8000, 1); rcode = async_open(&port, COM1, "2400N81"); /** or rcode = async_open(&port, 0x3f8, 0x10, 12, "2400N81"); ** or rcode = async_open(&port, 0x3f8, IRQ4, VCTR4, "2400N81"); **/ if (rcode != R_OK) { printf("\nAsync_open failed, exit code = %d", rcode); exit(rcode); } async_open --------------------------------------------------------------- Example 2: /* Open a port located at 0x2e0 that uses IRQ3. In this case NEAR ring buffers are specified and the memory for the port structure is obtained using malloc. See the AllocRingBuffer function described previously. */ #include "comm.h" ASYNC *port; int rcode; if ((port = (ASYNC *)malloc(sizeof ASYNC)) == NULL) { printf("\nNot enough memory"); exit(R_NOMEM); } AllocRingBuffer(port, 4096, 1200, 0); rcode = async_open(port, 0x2e0, IRQ3, VCTR3, "115200E71"); if (rcode != R_OK) { printf("\nAsync_open failed, exit code = %d", rcode); exit(rcode); } async_open --------------------------------------------------------------- Example 3: /* Open both COM1 and COM2 at the same time. You can open two ports at once as long as they don't share the same IRQ line or interrupt vector. */ #include "comm.h" ASYNC ports[2], *port[2]; int rcode; port[0] = &ports[0], port[1] = &ports[1]; AllocRingBuffer(port[0], 10240, 10240, 1); rcode = async_open(port[0], COM1, "9600N81"); if (rcode != R_OK) { printf("\nAsync_open failed, exit code = %d", rcode); exit(rcode); } AllocRingBuffer(port[1], 10240, 10240, 1); rcode = async_open(port[1], COM2, "1200E71"); if (rcode != R_OK) { printf("\nAsync_open failed, exit code = %d", rcode); exit(rcode); } async_open --------------------------------------------------------------- Example 4: /* Open COM1 using its current baud, parity, data, and stop bit settings. The port structure member, BPDSstr, will reflect those settings after calling async_open. */ #include "comm.h" ASYNC *port; int rcode; /* alloc port structure & ring buffer memory */ port = malloc(sizeof(ASYNC)); AllocRingBuffer(port, 4096, 2048, 1); /* empty parameter string causes port to be opened at its current settings */ rcode = async_open(port, COM1, ""); if (rcode != R_OK) { printf("\nAsync_open failed, exit code = %d", rcode); exit(rcode); } printf( "\nBaud, parity, data, stop bits = %s\n", port->BPDSstr); async_open --------------------------------------------------------------- Returns: R_OK (0) - the port was opened with no errors. R_NOMEM - a NULL pointer was passed as the address of the ring buffers. Probable causes are either failing to initialize the port structure ring buffer variables or assigning the RingSeg and RingOfst structure a NULL pointer. This could occur if you use the AllocRingBuffer function or something similar and the call to malloc fails. R_BAUDERR - the passed baud rate in the BPDS string was invalid. Some possible reasons for this error are leading spaces in the parameter string or use of commas. "115200N81" is correct. " 115200N81" and "115,200N81" are both incorrect. R_PARITYERR - an invalid character was found in the parameter string where the parity should have been. Commas or spaces in the parameter string are possible causes. Valid parity settings are N - none, E - even, or O - odd. See R_BAUDERR. R_DTABITERR - an invalid number of data bits was spec- ified. Only settings of 7 or 8 are supported. R_STPBITERR - an invalid number of stop bits was spec- ified. Stop bits must be set to either 1 or 2. R_IRQUSED - an attempt was made to open two ports that use the same IRQ line. R_VCTRUSED - an attempt was made to open two ports that use the same interrupt vector. R_NOPORT - an attempt was made to open more than 2 simultaneous ports. R_PORTUSED - an attempt was made to open two ports that have the same I/O address. R_UARTERR - an attempt was made to open a port that is stuck in an interrupt condition (see the notes on problems with the WD16550 at the beginning of this documentation ). async_open --------------------------------------------------------------- Remarks (16550 support): This function now automatically detects the presence of a 16550 UART and enables FIFO operation if one is detected. By ORing either 0x8000 or 0x4000 with the ComBase argument, you can change the default of auto- enabling FIFO mode. If 0x8000 is ORed with the ComBase argument (ex: 0x8000|0x3f8), no attempt is made to detect a 16550 and no changes are made to the mode of operation of the 16550 if one is present. If this bit is set, none of the functions or bits relating to the 16550 UART will be valid. If 0x4000 is ORed with the ComBase, the 16550 will be forced into non-FIFO mode. ORing 0x2000 with the ComBase parameter will open the port with MSR interrupts disabled. ORing the ComBase parameter with 0x1000 will open the port with LSR interrupts disabled. See the notes on the WD16550 at the beginning of this documentation for why this may be desired and the side effects of opening a port with MSR interrupts disabled. When async_open is called, the FIFOs are momentarily disabled and then re-enabled with the receive trigger level set to 1 byte. In versions of MCOMM prior to 5.40, the FIFOs were not reset if they were already on. Resetting the FIFOs was added to correct occasional rare problems with the port not opening. /* detect 16550, enable FIFOs if present */ async_open(PortPtr, 0x3f8, IRQ, Vector, Params); /* do not attempt to detect 16550 */ async_open(PortPtr, 0x8000|0x3f8, IRQ, Vctr, Params); /* detect 16550, disable FIFOs if present */ async_open(PortPtr, 0x4000|0x3f8, IRQ, Vctr, Params); /* open port, disable MSR interrupts */ async_open(PortPtr, 0x2000|0x3f8, IRQ, Vctr, Params); /* open port, disable MSR interrupts and FIFOs */ async_open(PortPtr, 0x6000|0x3f8, IRQ, Vctr, Params); async_open --------------------------------------------------------------- Remarks (versions previous to 5.00): There are some major differences in the async_open function in MCOMM5 and previous versions of the rou- tines. The two most major ones are that the parame- ters passed to the function are different and it is now necessary to allocate the memory for the ring buffers before calling the function. To make things simpler, COM1 and COM2 are defined in COMM.H and the function, AllocRingBuffer, is provided. The COM1 and COM2 definitions satisfy the requirements for the 2nd, 3rd, and 4th parameters required by the function. For ports other than the standard COM1 and COM2, it is necessary to list the individual arguments. The func- tion, AllocRingBuffer, is provided in C source form on the disk and included in the COMM_x libraries. This function allocates the ring buffer memory and initial- izes the required port structure members. The return values for async_open are different and may have a different meaning than in earlier versions. If a port is opened with an empty parameter string (using "" for the parameters), then the port is opened at its current settings and the port member BPDSstr is set to the string representation of those values. Async_open no longer checks the BIOS ram area at 40:0 to verify that a port actually exists. There were too many compatibles that did not store the proper values there. The maximum combined size of the receive and transmit buffers for each port is 32K - 1. FAR ring buffers in small and medium memory model programs is now supported. Use of FAR buffers does not in any way affect the speed of the routines. async_peek --------------------------------------------------------------- Purpose: Indexed receive ring buffer look ahead function. Format: int async_peek(port, index); ASYNC *port; Pointer to ASYNC structure int index; Index value Examples: ASYNC *port; char ch, buf[10]; int i; /* peek next char in receive ring buffer */ ch = async_peek(port, 0); /* peek next 10 chars in receive ring buffer */ for (i = 0; i < 10; i++) buf[i] = async_peek(port, i); Returns: This function returns the character in the receive ring buffer at the indexed position. If an attempt is made to peek deeper in the ring buffer than there are characters in the ring buffer, -1 (0xffff) is returned. Remarks: No characters are removed from the ring buffer by this function. The index value is 0 based. To avoid confusing the character, '\0xff', from the error return value, 0xffff, use an integer size variable for the return value. The character '\0xff' is returned as 0x00ff and the error condition is returned as 0xffff. async_regs --------------------------------------------------------------- Purpose: Provides direct access to the UART registers. Format: int async_regs(port, reg_ofst, value); ASYNC *port; Pointer to ASYNC structure int reg_ofst; Offset of register from base adrs int value; Value to write or -1 if reading Examples: ASYNC *port; int LCRvalue; /* read the line control register */ LCRvalue = async_regs(port, LCRreg, RDreg); /* write a 0 to the modem control register */ async_regs(port, MCRreg, 0); Returns: When reading a register, the return value is the value of the UART register that was read. When writing a register, the return value is undefined. Remarks: The following values for register offsets are defined in COMM.H for use with async_regs: RXreg, TXreg - receive & transmit regs, value = 0 IERreg - interrupt enable register, value = 1 IIDreg - interrupt identification reg, value = 2 FCRreg - FIFO control register value = 2 LCRreg - line control register, value = 3 MCRreg - modem control register, value = 4 LSRreg - line status register, value = 5 MSRreg - modem status register, value = 6 LObaud - offset of low baud divisor, value = 0 HIbaud - offset of high baud divisor, value = 1 Also RDreg is defined as -1 for use when reading one of the UART registers. See the examples. See cautions on the following page before using this function. async_regs --------------------------------------------------------------- Remarks (continued): This function is provided primarily as a debugging tool. Reading or writing to the UART registers while operating in an interrupt driven mode can cause several types of problems. Do not use this function unless you know what you are doing. Do not read the RXreg, IIDreg, LSRreg, or MSRreg on an open port except for debugging purposes. Do not write any of the registers. The function may be used on a port that has not yet been opened if the ComBase member of the port struc- ture has been set. When async_regs is used with an unopened port the UART registers may be read or writ- ten without restriction. async_reset --------------------------------------------------------------- Purpose: Clear parity error bit, framing error bit, character overrun bit, receive buffer overflow bit, and break signal received bit in the the Stat1 byte. Format: void async_reset(port); ASYNC *port; Pointer to ASYNC structure Example: ASYNC *port; if (error) async_reset(port); Returns: No return value Remarks: This function is implemented as a macro. See also async_rx and async_stat. async_restart --------------------------------------------------------------- Purpose: Re-initialize an already opened serial port Format: void async_restart(port); ASYNC *port; Pointer to ASYNC structure Example: ASYNC *port; async_restart(port); Returns: No return value Remarks: Async_restart resets the interrupt vector, UART regis- ters, and 8259 interrupt controller mask to the values necessary for interrupt driven operation. It also flushes the receive and transmit buffers and resets the Stat1 byte. Use this function to restart a comm port after spawning a program that may have altered the interrupt vector, UART regs, or interrupt mask. See also async_stop. async_rts --------------------------------------------------------------- Purpose: Sets or resets the Request to Send signal. Format: void async_rts(port, flag); ASYNC *port; Pointer to ASYNC structure int flag; Set/Reset RTS flag Example: ASYNC *port; if (WantToDropRTS) async_rts(port, 0); else if (WantRTShigh) async_rts(port, 1); Returns: No return value Remarks: The RTS signal is primarily used for hardware hand- shaking. When a port is first opened RTS is set HIGH (enabled). When the port is closed, it is restored to the condition it was in when the port was opened. To force RTS low when closing a port, regardless of its state when the port was opened, AND the port member, OldMCR with NOT B_RTS. To force RTS to remain high when the port is closed, OR OldMCR with B_RTS. Force low: port->OldMCR &= ~B_RTS; async_close(port); Force high: port->OldMCR |= B_RTS; async_close(port); async_rx --------------------------------------------------------------- Purpose: Gets one character from the receive ring buffer. Format: int async_rx(port); ASYNC *port; Pointer to ASYNC structure Examples: ASYNC *port; int rxch; rxch = async_rx(port); /* rxch == Stat1/char */ rxch = async_rx(port) & 0xff; /* rxch == char */ /* chk if char available & process only if it was */ if (!((rxch = async_rx(port)) & B_RXEMPTY) procRxdChar(rxch & 0xff); Returns: Async_rx returns the character received as the low byte and the Stat1 status byte as the high byte. If the receive ring buffer was empty when async_rx was called the low byte will be 0 and the high byte will have the B_RXEMPTY bit set. The Stat1 byte is a bit mapped value that reflects parity errors, framing errors, character overrun errors, receive buffer overflow errors, receive buffer empty, break signal received, and carrier lost. If no receive errors have occurred, a break signal has not been received, and a carrier is present, Stat1 will be 0. async_rx --------------------------------------------------------------- Remarks: Error bits set in the Stat1 byte are not necessarily associated with the character just taken out of the receive ring buffer. In fact, they probably are not. The error bits are set when the error is detected and reset when async_reset is called. For example: 1) 20 bytes of data are received with no errors. 2) Async_rx has been called 10 times so 10 characters have been taken out of the ring buffer and 10 of the bytes with no errors are still in the buffer. 3) A parity error occurs on the next byte received from the UART -- the 11th byte in the receive ring buffer. 4) The next byte taken out of the buffer, which is the first of the 10 remaining good bytes will have the parity error bit in the Stat1 byte. It will remain set until async_reset is called. If the 'ignore characters with errors' bit is set (see async_ignerr), then characters that have either parity or framing errors are never placed in the receive ring buffer. They are read from the UART and discarded. The error bits in Stat1 are set regardless of the setting of the 'ignore characters with errors' bit. async_rxblk --------------------------------------------------------------- Purpose: Retrieves a block of characters from the receive ring buffer. Format: int async_rxblk(port, buf, maxchars); ASYNC *port; Pointer to ASYNC structure char *buf; Buffer for received data int maxchars; Maximum number of chars to read Example: ASYNC *port; char buf[256]; int bytesRead; bytesRead = async_rxblk(port, buf, sizeof(buf)); Returns: Async_rxblk returns the number of bytes read. This value will be 'maxchars' if there are that many bytes available in the receive buffer. If there are not 'maxchars' in the receive buffer, the entire contents of the receive buffer will be moved to 'buf' and the return value will be the number of bytes that were in the buffer. Remarks: Very fast way to read data. See also async_rx and async_rxblkch. async_rxblkch --------------------------------------------------------------- Purpose: Retrieve bytes from the receive ring buffer until the specified character is found, 'maxchars' are read, or the receive ring buffer is emptied. Format: int async_rxblkch(port, buf, maxchars, keychar, includekey); ASYNC *port; Pointer to ASYNC structure char *buf; Destination for bytes read int maxchars; Maximum number of chars to read char keychar; Character to scan for int includekey; Flag set if 'keychar' is to be read also Example: ASYNC *port; char buf[256]; int bytesRead; int foundkey; bytesRead = async_rxblkch(port, buf, sizeof(buf), '\n', 1); if (bytesRead < 0) bytesRead = -bytesRead, foundkey = TRUE; else foundkey = FALSE; Returns: This function returns the number of bytes read if the 'keychar' is not found. If the 'keychar' is found the 2's complement of the number of bytes read is returned. async_rxblkch --------------------------------------------------------------- Remarks: The 'includekey' flag, which is the last argument of the function, determines whether or not the 'keychar' is to be included if it is found. If the flag is 1 and the 'keychar' is found it will be the last char- acter in the user buffer. If this flag is 0 and the 'keychar' is found, the 'keychar' is left in the re- ceive ring buffer and will be the first character read when you next call one of the async_rx type functions. This can cause a problem if you set this flag to 0 and the 'keychar' is the first character in the receive buffer. The function will return 0, which would seem to indicate that there were no bytes in the buffer. Actually the character was found but since you are not taking it out of the ring buffer zero bytes are read. There are two ways to check for this condition. You can first call async_rxcnt to verify there are bytes in the receive buffer and then call async_rxblkch. If async_rxblkch returns 0, the 'keychar' is there and is the first byte in the buffer. The other method is to use async_peek to see what the next character in the receive buffer is before calling async_rxblkch. A 2's complement value of the bytes read is returned by async_rxblkch when the 'keychar' is found. For actual bytes use: bytes = async_rxblkch( ....); if (bytes < 0) bytes = -bytes; A byte count less than zero is the signal the 'keychar' was found. (Except for the circumstance noted in the previous paragraph). See async_rx, async_rxblk, async_rxcnt, async_peek. async_rxcnt --------------------------------------------------------------- Purpose: Returns the number of bytes in the receive ring buffer. Format: int async_rxcnt(port); ASYNC *port; Pointer to ASYNC structure Example: ASYNC *port; BytesInRxBuf = async_rxcnt(port); Returns: Number of bytes in the receive ring buffer Remarks: This function is implemented as a macro. async_rxerr --------------------------------------------------------------- Purpose: Checks if a receive error has been detected. Format: int async_rxerr(port); ASYNC *port; Pointer to ASYNC structure Example: ASYNC *port; int rxerr_status; rxerr_status = async_rxerr(port); Returns: ZR if no receive errors have been detected, NZ if receive error has been detected. Remarks: Types of receive errors that are detected by this function are parity errors, framing errors, UART receive register overflow, and receive ring buffer overflow. This information is also returned as the high byte of the async_rx and async_stat functions. This function is implemented as a macro. See also async_rx, async_stat. async_rxflush --------------------------------------------------------------- Purpose: Empties out the receive ring buffer. Format: void async_rxflush(port); ASYNC *port; Pointer to ASYNC structure Example: ASYNC *port; async_rxflush(port); Returns: This function does not have a return value Remarks: Clears the receive ring buffer and -- if a 16550 is present in the system with its FIFOs activated -- resets the receiver FIFOs. All data that was in the buffer is lost. If XON/XOFF flow control is being used and an XOFF has been sent to the remote, this function automatically sends an XON. An XON is not ALWAYS sent -- only if XFLOW control is in use and the async interrupt routine has sent an XOFF. It will not clear false XOFFs the remote may have received. async_rxfree (5.40) --------------------------------------------------------------- Purpose: Returns the number of bytes left available in the receive ring buffer for incoming characters. Format: int async_rxfree(port); ASYNC *port; Pointer to ASYNC structure Example: ASYNC *port; RxBufFreeSpace = async_rxfree(port); Returns: Number of bytes that can be received without taking any out before a receive buffer overflow will occur. Remarks: This function is implemented as a macro. async_setbpds --------------------------------------------------------------- Purpose: Change the baud rate, parity, number of data bits or number of stop bits on an already opened port. Format: int async_setbpds(port, params); ASYNC *port; Pointer to ASYNC structure char *params; Pointer to parameter string Example: ASYNC *port; int rcode; rcode = async_setbpds(port, "2400E71"); Returns: This function returns 0 if successful and the new parameter string is copied to the port structure member, BPDSstr. Errors that can be returned are R_BAUDERR, R_PARITYERR, R_DTABITERR, or R_STPBITERR. If one of these error codes are returned, the port settings are unchanged and the port member BPDSstr is left unchanged. See async_open for a more complete description of these errors. Remarks: If 7 data bits is selected the StripMask is set to strip the high bit off incoming data. If 8 data bits are selected the StripMask is disabled. Valid baud rates are from 50 to 115200 baud. Parity may be 'E'ven, 'N'one, or 'O'dd. The number of data bits must be 7 or 8 and the number of stop bits must be 1 or 2. Do not use spaces, commas, or any other type of punctuation in the parameter string. See also async_open, async_strip. async_sndbrk --------------------------------------------------------------- Purpose: Enable or disable a break signal Format: void async_sndbrk(port, Brkflag); ASYNC *port; Pointer to ASYNC structure int Brkflag; Set/Reset break signal flag Example: ASYNC *port; /* send break for 50 msec */ async_sndbrk(port, 1); /* enable break signal */ delay(50MSEC); /* your delay function */ async_sndbrk(port, 0); /* disable break signal */ Returns: No return value Remarks: This function causes the UART to send a continuous break signal if it is called with the flag set to 1. It must be called again with the flag set to 0 to disable the break signal. async_stat --------------------------------------------------------------- Purpose: Get the current status of a port Format: int async_stat(port, mask); ASYNC *port; Pointer to ASYNC structure int mask; Mask applied to return value Examples: ASYNC *port; int status; /* status = all status bits */ status = async_stat(port, 0xffff); /* check for XOFF received condition */ if (async_stat(port, B_XRXD)) do_something(); Returns: Returns Stat1/Stat2 status bits after masking them with the passed mask value. Stat1 is the high byte and Stat2 is the low byte of the return value. Stat1 bit map: Bit 7 = set if no carrier present Bit 6 = receive ring buffer empty Bit 5 = used by interrupt routines (always 0) Bit 4 = break signal was detected Bit 3 = framing error was detected Bit 2 = parity error was detected Bit 1 = character overrun error was detected Bit 0 = receive ring buffer has overflowed Stat2 bit map: Bit 7 = carrier detect monitored for flow control Bit 6 = XOFF rx'd or hardware flow control active Bit 5 = data set ready monitored for flow control Bit 4 = clear to send monitored for flow control Bit 3 = transmit ring buffer is empty Bit 2 = an XOFF has been sent by interrupt handler Bit 1 = an XOFF has been received Bit 0 = using XON/XOFF flow control async_stat --------------------------------------------------------------- Remarks: For some situations, it is more efficient to use one of the other library functions targeted specifically for the information you want. For instance, instead of calling: async_stat(port, B_XRXD); use: async_xrxd(port); The information in the Stat1 byte is also returned as the high byte of the async_rx function. Bits 0-4 of Stat1 remain set until cleared by the async_reset function. Not all bits in the Stat2 and Stat1 port structure members are kept updated on a constant basis so do not try to check a condition by testing the Stat1 or Stat2 values in the ASYNC structure. Use one of the docu- mented functions or macros to be sure of getting the correct result. async_stop --------------------------------------------------------------- Purpose: Temporarily disables interrupt driven operation of an already opened port. Format: void async_stop(port); ASYNC *port; Pointer to ASYNC structure Example: ASYNC *port; int x, inhdl, outhdl, errhdl; async_stop(port); /* release port */ /* redirect console to async port */ x = open("COM1", O_RDWR|O_BINARY); inhdl = dup(0); outhdl = dup(1); errhdl = dup(2); dup2(x, 0); dup2(x, 1); dup2(x, 2); /* run a redirected DOS shell */ spawnlp(P_WAIT, "COMMAND.COM", "COMMAND.COM", NULL); /* restore stdin, stdout, stderr */ close(x); dup2(inhdl, 0); close(inhdl); dup2(outhdl, 1); close(outhdl); dup2(errhdl, 2); close(errhdl); async_restart(port); /* regain control of port */ Returns: No return value Remarks: Call this function before spawning a program that will be doing its own port I/O, such as an external commun- ications program or a redirected DOS shell. After the other application has completed, call async_restart to re-enable interrupt operation. This function disables interrupts for the named port by clearing UART's interrupt enable register and the OUT2 bit of its modem control register. See also async_restart. async_strip --------------------------------------------------------------- Purpose: Set the strip mask for received characters. Format: void async_strip(port, mask); ASYNC *port; Pointer to ASYNC structure char mask; Strip mask Example: ASYNC *port; async_strip(port, '\x7f'); Returns: No return value Remarks: The strip mask is automatically set to 0x7f when the parameters are set for 7 data bits and to 0xff when 8 data bits are used. All incoming data is ANDed with the strip mask before it is placed in the receive ring buffer. This function is implemented as a macro. async_tx --------------------------------------------------------------- Purpose: Send 1 character to a port. Format: int async_tx(port, ch); ASYNC *port; Pointer to ASYNC structure char ch; Character to transmit Example: ASYNC *port; /* send a CR/LF to a port */ async_tx(port, '\r'); async_tx(port, '\n'); Returns: Returns the number of bytes left available in the transmit ring buffer unless the ring buffer was full when the function was called. R_TXERR is returned if the transmit ring buffer was full and the character that was to be transmitted is not placed in the ring buffer. Remarks: The error return value, R_TXERR, is a negative number. The bytes free return value can never be negative. See also async_txblk, async_txfree. async_txblk --------------------------------------------------------------- Purpose: Send a block of characters to a port. Format: int async_txblk(port, buf, count); ASYNC *port; Pointer to ASYNC structure char *buf; Pointer to block to transmit int count; Size of block in bytes Examples: ASYNC *port; char buf[128]; static char *msg = "Send this message\r\n"); put_data_in_buf(); async_txblk(port, buf, sizeof(buf)); async_txblk(port, msg, strlen(msg)); Returns: Returns the number of bytes left available in the transmit ring buffer unless the ring buffer would not hold the entire block when the function was called. R_TXERR is returned if there was no room for the block and none of the bytes in the block are sent. Remarks: This function is much faster than using repeated calls to async_tx when multiple bytes are being transmitted. The error return value, R_TXERR, is a negative number. The bytes free return value can never be negative. See also async_tx, async_txfree. async_txcnt (5.40) --------------------------------------------------------------- Purpose: Returns the number of bytes in the transmit ring buffer. Format: int async_txcnt(port); ASYNC *port; Pointer to ASYNC structure Example: ASYNC *port; BytesInTxBuf = async_txcnt(port); Returns: Number of untransmitted bytes in the transmit ring buffer. Remarks: This function is implemented as a macro. If a 16550 is in the system with its FIFOs active, there may be up to 16 (depends on what async_FIFOtxlvl is set at -- the default is 3 bytes) more bytes of untransmitted data in the 16550 FIFOs plus 1 byte in the UART transmit hold register. With no 16550 there may still be up to 2 untransmitted bytes -- one in the UART's transmit hold register and one in the UART's transmit shift register. To monitor for a transmit buffer empty condition use async_txempty. async_txempty --------------------------------------------------------------- Purpose: Checks if transmit ring buffer is empty. Format: int async_txempty(port); ASYNC *port; Pointer to ASYNC structure Example: ASYNC *port; /* wait for transmit ring buffer to empty out */ while (!async_txempty(port)) ; Returns: NZ if the transmit ring buffer is empty, ZR if the buffer still has characters to be transmitted. Remarks: This function is implemented as a macro. If a 16550 is in the system with its FIFOs active, there may be up to 16 (depends on what async_FIFOtxlvl is set at -- the default is 3 bytes) more bytes of untransmitted data in the 16550 FIFOs plus 1 byte in the UART transmit hold register. With no 16550 there may still be up to 2 untransmitted bytes -- one in the UART's transmit hold register and one in the UART's transmit shift register. async_txflush --------------------------------------------------------------- Purpose: Flushes the transmit ring buffer. Format: void async_txflush(port); ASYNC *port; Pointer to ASYNC structure Example: ASYNC *port; async_txflush(port); Returns: No return value Remarks: Clears the transmit ring buffer and -- if a 16550 operating in FIFO mode is in the system -- resets the transmit FIFOs. All characters in the buffer that have not been transmitted are lost. async_txfree --------------------------------------------------------------- Purpose: Returns the number of bytes left available in the transmit ring buffer. Format: int async_txfree(port); ASYNC *port; Pointer to ASYNC structure Example: ASYNC *port; int tx_bytes_available; tx_bytes_available = async_txfree(port); Returns: Number of bytes of free space left in the transmit buffer. Remarks: The number of free bytes left in the transmit ring buffer is also the return value of async_tx and async_txblk. This function is implemented as a macro. async_xany --------------------------------------------------------------- Purpose: Checks if accepting the first character after an XOFF is received as the XON character. DOES NOT enable any character XON (use async_xflow). Format: int async_xany(port); ASYNC *port; Pointer to ASYNC structure Example: ASYNC *port; int rcode; rcode = async_xany(port); Returns: Not zero if first character after an XOFF is to be treated as an XON. Zero if a real XON is required to clear an XOFF. Remarks: This function is implemented as a macro. See also async_xflow. async_xflow --------------------------------------------------------------- Purpose: Enables/disables use of XON/XOFF flow control. Format: void async_xflow(port, flag); ASYNC *port; Pointer to ASYNC structure int flag; Enable/Disable & any char XON flag Examples: ASYNC *port; async_xflow(port, B_XUSE); /* use flow control */ async_xflow(port, 0); /* disable flow control */ /* use XON/XOFF flow control with any char being accepted as an XON */ async_xflow(port, B_XUSE | B_XONANY); /* enable XON/XOFF on transmit side only */ async_xflow(port, B_XUSET); /* enable XON/XOFF on receive side only */ async_xflow(port, B_XUSER); Returns: No return value Remarks: Passing B_XUSET enables the transmission of XON/XOFF characters when the receive buffer fills to the 'trip' levels discussed in the following paragraph. Incoming XON/XOFFs are not regarded as flow control characters and are stored in the ring buffer. Passing B_XUSER, enables recognition of received XON/XOFFs as flow characters but does not enable transmission of XON/XOFF at the trip levels. If B_XUSE is passed, both transmission and recognition of XON/XOFF as flow characters is enabled (the same as B_XUSET | B_XUSER). ORing B_XONANY with either B_XUSE or B_XUSER causes the first character received after an XOFF to be treated as the XON unless that character is another XOFF. Passing zero as the flag disables XON/XOFF flow control. The default is no flow control. async_xflow --------------------------------------------------------------- Remarks (continued): The port structure member, XoffTrip, determines when an XOFF will be sent. Whenever the number of bytes left available in receive buffer falls below XoffTrip, an XOFF is sent. The default value of XoffTrip is 25% of the size of the receive buffer so an XOFF is sent whenever the receive buffer is 75% full. The port structure member, XonTrip, determines when an XON will be sent. Whenever the number of bytes left available in the receive buffer rises above XonTrip, an XON will be sent. Its default value is 50% of the size of the receive buffer. The port structure member, XTxRptInit, determines how many bytes may be received after an XOFF is sent before another XOFF is sent. Its default value is 6.25% of the size of the receive buffer or 160 bytes, whichever is less. XoffTrip, XonTrip, and XTxRptInit may all be changed from their default values by directly accessing the port structure. To do this: ASYNC *port; /* send XOFF when 300 bytes left in rx ring buf */ port->XoffTrip = 300; /* send XON when 350 bytes left in rx ring buf */ port->XonTrip = 350; Be sure to keep the XonTrip level higher than the XoffTrip level. The values are for bytes left available not bytes used. The XTxRptInit value is used to automatically send another XOFF in the event the first one was ignored. Instead of sending an XOFF character everytime another character is received, the interrupt routines wait for 'XTxRptInit' characters to be received and then repeat the XOFF. If this value is set to low some systems that allow any character to be an XON will treat the repeated XOFF character as an XON. async_xoffclr --------------------------------------------------------------- Purpose: Manually clears an XOFF received condition Format: void async_xoffclr(port); ASYNC *port; Pointer to ASYNC structure Example: ASYNC *port; async_xoffclr(port); Returns: No return value Remarks: Async_xoffclr has the same effect as if the remote system had sent an XON. This will unstop the system in the event a false XOFF is received or the remote's XON was lost. Use this function with caution. Unless something goes wrong, the remote will clear XOFF cond- itions automatically by sending an XON. If an XOFF is manually cleared, the remote site may be overran and lose data. For use only when XON/XOFF flow control has been activated. See also async_xoffset. async_xoffset --------------------------------------------------------------- Purpose: Manually sets an XOFF received condition Format: void async_xoffset(port); ASYNC *port; Pointer to ASYNC structure Example: ASYNC *port; async_xoffset(port); Returns: No return value Remarks: Forces the local site to act as though an XOFF had been received. Transmit interrupts are disabled until the remote sends an XON or you call async_xoffclr. For use only when XON/XOFF flow control has been activated. See also async_xoffclr. async_xrxd --------------------------------------------------------------- Purpose: Check if an XOFF has been received and has activated a flow control halt. Format: int async_xrxd(port); ASYNC *port; Pointer to ASYNC structure Example: ASYNC *port; int rcode; rcode = async_xrxd(port); Returns: Not zero if an XOFF has been received and an XON has not been received to clear it. Returns zero if XOFF flow halt is not currently active. Remarks: This function is implemented as a macro. See also async_xoffclr, async_xtxd. async_xtxd --------------------------------------------------------------- Purpose: Check if an XOFF has been sent Format: int async_xtxd(port); ASYNC *port; Pointer to ASYNC structure Example: ASYNC *port; int rcode; rcode = async_xtxd(port); Returns: Not zero if an XOFF has not been sent by the receive interrupt routine and an XON has not been sent to clear it. Returns zero if an XOFF has not been sent. Remarks: This function is implemented as a macro. See also async_xoffclr, async_xrxd. async_xuse --------------------------------------------------------------- Purpose: Check if XON/XOFF protocol is currently being used Format: int async_xuse(port); ASYNC *port; Pointer to ASYNC structure Example: ASYNC *port; rcode = async_xuse(port); Returns: Not zero if XON/XOFF protocol is being used on either the transmit or receive sides, zero if XON/XOFF flow is not being used at all. Remarks: This function is implemented as a macro. See async_xflow, async_xuset, async_xuser. async_xuser --------------------------------------------------------------- Purpose: Check if XON/XOFF protocol is enabled on the receive side (receiver recognizes XON/XOFF as flow control). Format: int async_xuser(port); ASYNC *port; Pointer to ASYNC structure Example: ASYNC *port; rcode = async_xuser(port); Returns: Not zero if XON/XOFF protocol is being used on the receive side, zero if it is not. Remarks: This function is implemented as a macro. See async_xflow, async_xuset, async_xuse. async_xuset --------------------------------------------------------------- Purpose: Check if XON/XOFF protocol is enabled on the transmit side (transmitter sends XOFF/XON as receive buffer bytes available crosses trip levels). Format: int async_xuset(port); ASYNC *port; Pointer to ASYNC structure Example: ASYNC *port; rcode = async_xuset(port); Returns: Not zero if XON/XOFF protocol is being used on the transmit side, zero if it is not. Remarks: This function is implemented as a macro. See async_xflow, async_xuser, async_xuse.