Super Net 1

home *** CD-ROM | disk | FTP | other *** search

/ Super Net 1 / SUPERNET_1.iso / PC / OTROS / MSDOS / NCSA / TEL2307S.ZIP / NET / ENET / NET503.ASM < prev next >

Wrap

Assembly Source File | 1991-10-20 | 22.5 KB | 1,100 lines

; 3C503 Driver ; ; Kurt Mahan ( based on WD8003 by Tim Krauskopf ) ; ;**************************************************************************** ;* * ;* * ;* part of NCSA Telnet * ;* by Tim Krauskopf, VT100 by Gaige Paulsen, Tek by Aaron Contorer * ;* neat other things by Kurt Mahan ;* * ;* National Center for Supercomputing Applications * ;* 152 Computing Applications Building * ;* 605 E. Springfield Ave. * ;* Champaign, IL 61820 * ;* * ;* * ;**************************************************************************** ; TITLE NETSUPPORT -- LOW LEVEL DRIVERS FOR ETHERNET ; ; Assembler support for interrupt-driven Ethernet I/O on the PC ; ; Reads and writes from the 8K buffer on the WD card. ; Started 4/11/88 ; ;Microsoft EQU 1 ;Lattice EQU 1 ifndef Microsoft ifndef Lattice if2 %out %out ERROR: You have to specify "/DMicrosoft" OR "/DLattice" on the %out MASM command line to determine the type of assembly. %out endif end endif endif ifdef Microsoft X EQU 6 DOSSEG .MODEL LARGE else NAME NET503 INCLUDE DOS.MAC SETX endif ; ; EQUATES for the 3C503 board ; CMDR equ 00h ; ports on the 8390 ( page 0 ) PSTART equ 01h PSTOP equ 02h BNRY equ 03h TPSR equ 04h TBCR0 equ 05h TBCR1 equ 06h ISR equ 07h RSAR0 equ 08h RSAR1 equ 09h RBCR0 equ 0ah RBCR1 equ 0bh XRCR equ 0ch TCR equ 0dh DCR equ 0eh IMR equ 0fh PAR0 equ 01h ; ports on the 8390 ( page 1 ) PAR1 equ 02h PAR2 equ 03h PAR3 equ 04h PAR4 equ 05h PAR5 equ 06h CURR equ 07h MAR0 equ 08h MAR1 equ 09h MAR2 equ 0ah MAR3 equ 0bh MAR4 equ 0ch MAR5 equ 0dh MAR6 equ 0eh MAR7 equ 0fh PSTR equ 400h ; ports on the gate array PSPR equ 401h DQTR equ 402h BCFR equ 403h PCFR equ 404h GACFR equ 405h CTRL equ 406h STREG equ 407h IDCFR equ 408h DAMSB equ 409h DALSM equ 40ah VPTR2 equ 40bh VPTR1 equ 40ch VPTR0 equ 40dh RFMSB equ 40eh RFLSB equ 40fh STRT_PG equ 26h ; start at page 6 STOP_PG equ 40h ; end at page 31 TSTRT_PG equ 20h ; transmit start page ; ; macros for writing to NET503 board ; ;*********************************************************************** ; ; Macros, from example driver ; ;*********************************************************************** ; ; MACRO rd_wd8 ; Reads port specified on macro call. Leaves byte in AL. ; rd_wd8 MACRO port push dx mov DX, WDBASE add DX, port ; DX contains address of port in AL, DX ; AL contains data read from port pop dx ENDM ; ; MACRO wr_wd8 ; Writes byte in AL to port specified on macro call. ; wr_wd8 MACRO port push dx mov DX, WDBASE add DX, port ; DX contains address of port out DX, AL ; AL contains data to be written to port pop dx ENDM ; ifdef Microsoft ;DGROUP group _DATA ;_DATA segment public 'DATA' ; assume DS:DGROUP .data else DSEG endif ; PUBLIC STAT,BUFPT,BUFORG,BUFEND,BUFREAD,BUFBIG,BUFLIM,OFFS ; ; The pointers below are actually DWORDs but we access them two ; bytes at a time. ; ; STAT change to RSTAT because of name clash with MSC library routine ifdef Microsoft EXTRN _RSTAT:BYTE ; last status from read EXTRN _BUFPT:WORD ; current buffer pointer EXTRN _BUFORG:WORD ; pointer to beginning of buffer EXTRN _BUFEND:WORD ; pointer to end of buffer EXTRN _BUFREAD:WORD ; pointer to where program is reading EXTRN _BUFBIG:WORD ; integer, how many bytes we have EXTRN _BUFLIM:WORD ; integer, max bytes we can have else EXTRN RSTAT:BYTE ; last status from read EXTRN BUFPT:WORD ; current buffer pointer EXTRN BUFORG:WORD ; pointer to beginning of buffer EXTRN BUFEND:WORD ; pointer to end of buffer EXTRN BUFREAD:WORD ; pointer to where program is reading EXTRN BUFBIG:WORD ; integer, how many bytes we have EXTRN BUFLIM:WORD ; integer, max bytes we can have endif WDBASE DW 00h ; base ioaddr WDADD DW 00h ; base shared mem addr DEAF DB 00H ; when we can't handle any more packets OFFS DW 00H ; how many times the handler was turned off WIRE DB 02h ; thin as the default ; ifdef Microsoft ;_DATA ends else ENDDS endif ; ; The subroutines to call from C ; ifdef Microsoft ;_TEXT segment public 'CODE' ; assume CS:_TEXT .code PUBLIC _E4RECV,_E4ETOPEN,_E4ETCLOSE,_E4GETADDR ifdef NOT_USED PUBLIC _E4SETADDR endif PUBLIC _E4XMIT,_E4ETUPDATE PUBLIC _E4SETWIRE else PSEG PUBLIC E4RECV,E4ETOPEN,E4ETCLOSE,E4GETADDR ifdef NOT_USED PUBLIC E4SETADDR endif PUBLIC E4XMIT,E4ETUPDATE, E4SETWIRE endif ;***************************************************************** ; ; E4SETWIRE ; ; WHAT TYPE OF WIRE ARE WE USING? THIN OR THICK ; ; USAGE: E4SETWIRE(INT WIRE) ; ifdef Microsoft _E4SETWIRE PROC FAR else E4SETWIRE PROC FAR endif PUSH BP MOV BP,SP push ds mov ax,seg WIRE mov ds,ax XOR AX,AX MOV AL,[BP+X] ; GET WIRE TYPE MOV WIRE,AL ; STORE IT! pop ds POP BP RET ifdef Microsoft _E4SETWIRE ENDP else E4SETWIRE ENDP endif ;****************************************************************** ; ETOPEN ; Initialize the Ethernet board, set receive type. ; ; usage: etopen(s,irq,addr,ioaddr) ; char s[6]; ethernet address ; int irq,addr,ioaddr; ; interrupt number (unused), base mem address and ; i/o address to use ; ifdef Microsoft _E4ETOPEN PROC FAR else E4ETOPEN PROC FAR endif ; ; init addresses and things ; PUSH BP MOV BP,SP mov AX,[BP+X+8] ; install ioaddr mov WDBASE,AX mov AX,[BP+X+6] ; install shared mem addr mov WDADD,AX ; ; initialize the gate array ; push ds mov ax,seg WIRE mov ds,ax mov al,1 ; reset the board -- onboard xcvr or al,WIRE wr_wd8 CTRL mov al,0 ; done with reset -- still onboard xcvr or al,WIRE wr_wd8 CTRL wr_wd8 CTRL pop ds ; ; set the vector pointers ( VPTR0 - VPTR2 ) so that the shared memory ; won't go byebye on us accidentally ( point to ffff00h ) ; mov al,0ffh wr_wd8 VPTR2 wr_wd8 VPTR1 xor al,al wr_wd8 VPTR0 ; ; lookup the shared memory address ( such a neat card, huh -- we can ; actually read it up from the gate array ) ; ; PCFR : high bits = ( 7 .. 0 ) ; bit 7 = dc00 ; bit 6 = d800 ; bit 5 = cc00 ; bit 4 = c800 ; ; rd_wd8 PCFR ; read prom config register test al,80h ; dc00? jz eto100 mov WDADD,0da00h jmp SHORT etok eto100: test al,40h ; d800? jz eto200 mov WDADD,0d600h jmp SHORT etok eto200: test al,20h ; cc00? jz eto300 mov WDADD,0ca00h jmp SHORT etok eto300: test al,10h ; c800? jz eto400 mov WDADD,0c600h jmp SHORT etok ; eto400: mov ax,-1 ; mem not enabled pop bp ret ; ; ok, WDBASE is setup as the base memory address ; etok : mov al,0c9h ; dis ints, ram sel, bank 0 wr_wd8 GACFR ; ; setup the start/stop pages ; mov al,STRT_PG ; starting page wr_wd8 PSTR mov al,STOP_PG ; ending page wr_wd8 PSPR ; ; setup the interrupt and dma request stuff ; xor al,10h ; no ints, no dma channels wr_wd8 IDCFR ; interrupt/dma channel ctrl ; ; set DRQ timer to 8 ; mov al,8 wr_wd8 DQTR ; ; set dma msb to 20h ; mov al,TSTRT_PG ; transmit start page wr_wd8 DAMSB xor al,al ; 0 wr_wd8 DALSM ; cld ; ; initialize the LAN Controller register ; push ds mov ax,seg WIRE mov ds,ax mov al,0 or al,WIRE wr_wd8 CTRL ; make sure its switched in pop ds ; ; program for page 0 ; mov AL, 21h ; page 0, abort any pending dma wr_wd8 CMDR ; ; clear interrupt regs ; mov al, 0ffh wr_wd8 ISR ; ; initial DCR data configuration ; mov AL, 48h ; burst dma, fifo thresh = 8 bytes wr_wd8 DCR ; ; initial TCR ; xor AL, AL wr_wd8 TCR ; normal operation ; ; initial RCR to monitor mode ; mov AL, 20h ; monitor mode wr_wd8 XRCR ; ; set page start/page stop/ boundary ; mov AL,STRT_PG wr_wd8 PSTART mov al,STOP_PG wr_wd8 PSTOP mov al,STRT_PG ; go with the WD style of things wr_wd8 BNRY ; ; program for page 1 ; mov AL, 60h ; page 1, abort any pending dma wr_wd8 CMDR ; ; initial physical addr ; mov DX, WDBASE ; get board io base push DS mov ax,[bp+X+2] ; get seg from parms mov ds,ax mov CX, 6 ; should be 6 for Ethernet mov BX, [BP+X] ; ptr to adr in BX add DX, PAR0 ; i/o address of PAR0 in DX lopa: mov AL, [BX] ; get 1 byte into AL out DX, AL ; write to PAR inc BX inc DX loop lopa pop DS ; ; initial multicast filter, write all 0's into MAR0 - MAR7 ; mov CX, 8 mov DX, WDBASE add DX, MAR0 ; i/o address of MAR0 in DX xor AL, AL lopb: out DX, AL inc DX loop lopb ; ; set CURR page ; mov al,STRT_PG+1 wr_wd8 CURR ; ; program for page 0 ; mov al,21h ; page 0, stop any dma stuff wr_wd8 CMDR ; ; initial IMR ; xor al,al ; ***NCSA Telnet does not need interrupts wr_wd8 IMR ; enable interrupt mov al,0ffh wr_wd8 ISR ; ; clear byte counts ; xor AL, AL wr_wd8 RBCR0 wr_wd8 RBCR1 ; ; put 8390 on line ; mov al,22h ; start up the 8390 wr_wd8 CMDR ; ; program RCR to normal operation (MSK_AB, no MSK_AM) ; mov al,4 ; accept broadcast packets wr_wd8 XRCR ; mov al,0c9h wr_wd8 GACFR ; ; I'm happy to keep GACFR at c9 ( no interrupts ) ; ; return NO ERROR ; XOR AX,AX POP BP RET ; ifdef Microsoft _E4ETOPEN ENDP else E4ETOPEN ENDP endif ifdef NOT_USED ; ;****************************************************************** ; SETADDR ; set the Ethernet address on the board to 6 byte ID code ; ; usage: setaddr(s,basea,ioa); ; char s[6]; ethernet address to use ; int basea; shared memory base address ; int ioa; io address for board ; ifdef Microsoft _E4SETADDR PROC FAR else E4SETADDR PROC FAR endif PUSH BP MOV BP,SP ; ; not used for this board, set during etopen ; POP BP RET ifdef Microsoft _E4SETADDR ENDP else E4SETADDR ENDP endif endif ; NOT_USED ; ;******************************************************************* ; GETADDR ; get the Ethernet address off of the board ; ; usage: getaddr(s,address,ioaddr); ; char s[6]; will get six bytes from the PROM ; int address; ; int ioaddr; mem address and ioaddress to use ; ifdef Microsoft _E4GETADDR PROC FAR else E4GETADDR PROC FAR endif PUSH BP MOV BP,SP PUSH DS MOV AX,[BP+X+2] ; SEG of where to put info MOV DS,AX MOV BX,[BP+X] ; address of where to put info mov cx,6 mov dx,[BP+X+6] ; ioaddr for board ; ; set the gate array to look at the lower 16 bytes of the prom ; push ds mov ax,seg WIRE mov ds,ax mov al,1 or al,WIRE pop ds push dx add dx,CTRL out dx,al mov al,2 out dx,al mov al,6 out dx,al pop dx push dx ; getloop: in al,dx mov [bx],al ; store where we want inc dx inc bx loop getloop ; ; reset the gate array to normal mapping ; pop dx push ds mov ax,seg WIRE mov ds,ax mov al,0 ; still onboard xcvr or al,WIRE pop ds add dx,CTRL out dx,al POP DS POP BP RET ifdef Microsoft _E4GETADDR ENDP else E4GETADDR ENDP endif ; ;*********************************************************************** ; ETCLOSE ; shut it down, remove the interrupt handler ; ; usage: etclose(); ; ; ifdef Microsoft _E4ETCLOSE PROC FAR else E4ETCLOSE PROC FAR endif RET ifdef Microsoft _E4ETCLOSE ENDP else E4ETCLOSE ENDP endif ; ;************************************************************************ ; Receive ; This is a CPU hook for boards that must be polled before we can ; deliver packets into the receive buffer. (i.e. no interrupts used) ; ; usage: recv(); ; ifdef Microsoft _E4RECV PROC FAR else E4RECV PROC FAR endif push bp push es ; ; check for data which can be read ; rd_wd8 XRCR ; read the Rx Status Register and al,01h ; check for a packet jnz snore ; none -- go onto something else jmp end_rx snore: ; ; ok, the chip thinks we have a packet to read ; mov AL, 61h ; page 1 wr_wd8 CMDR rd_wd8 CURR mov BL, AL ; CURR in BL ; mov AL, 20h ; page 0 wr_wd8 CMDR rd_wd8 BNRY ; BNRY in AL ; add AL, 1 ; start page of frm in AL cmp AL, STOP_PG ; check boundary jne go_cmp mov AL, STRT_PG go_cmp: cmp AL, BL jne gotone jmp end_rx ; buff ring empty gotone: ; ; ring not empty ; mov BH, AL xor BL, BL ; BX has the rx_frm pointer push BX ; save the frm ptr mov AX, WDADD ; shared mem base mov ES, AX ; ES has the shr seg paragraph mov AL, ES:[BX] ; AL has the status byte ; test AL, SMK_PRX ; if rx good test al,1 jnz readit jmp fd_bnry ; rx error, drop frm by forward bnry readit: ; ; set up to read the next packet from the net ; ; ; get ready for next packet ; cld ; moves in fwd dir ; ; check for buffer overrun or catching up with reader ; ; implicit 64K max buffer, should stop before 64K anyway ; ifdef Microsoft MOV AX,_BUFBIG ; how much stuff is in buffer MOV BX,_BUFLIM ; what is our size limit? else MOV AX,BUFBIG ; how much stuff is in buffer MOV BX,BUFLIM ; what is our size limit? endif CMP AX,BX JNA ISROOM ; we are ok ; ; no room at the Inn. ; JMP SHORT fd_bnry ; can't do much, we lose packets until restarted ; ; wrap pointer around at end, we know that we have room ; ISROOM: ifdef Microsoft MOV DI,word ptr [_BUFPT] ; where buffer is MOV DX,word ptr [_BUFEND] ; right before 2K safety area else MOV DI,word ptr [BUFPT] ; where buffer is MOV DX,word ptr [BUFEND] ; right before 2K safety area endif CMP DX,DI ; see if pointer is over limit JA OKAYREAD ; we are not at wrap-around ifdef Microsoft MOV AX,word ptr [_BUFORG] ; wrap to here MOV word ptr [_BUFPT],AX ; wrap-around else MOV AX,word ptr [BUFORG] ; wrap to here MOV word ptr [BUFPT],AX ; wrap-around endif MOV DI,AX ; di also OKAYREAD: ; ; ; start the copy of the new packet ; pointer to the shared memory offset is in BX ; At this offset, you will find: ; 1 byte - read status, usually 21h ; 1 byte - pointer, page # of next packet ; 2 bytes - length of data in packet, swapped for you already ; n bytes - that many bytes of Ethernet packet spread ; over n div 256 pages (allowing four lost bytes in first packet) ; ; pop si ; get packet pointer back into si push si ; restore for fd_bnry to read ; ; save regs while moving packet to buffer ; set up ds for buffer, even though we switch it later ; push es push ds ifdef Microsoft MOV AX,word ptr [_BUFPT+2] ; buffer's ds else MOV AX,word ptr [BUFPT+2] ; buffer's ds endif mov ds,ax ; ; here, DS:DI contains where we want to put the packet. ; newpkt: add si,2 ; offset for length field mov dx,es:[si] ; value of length of recd packet mov [di],dx ; put the accumulated size there inc si inc si inc di inc di ; now it is the data pointer ; ; ; Actually move the data ; DX has packet size in bytes ; ES:SI has the source pointer } need to switch ; DS:DI has the dest pointer } es and ds ; Remember, 256 byte pages wrap around at STOP_PG and there ; are max 252 bytes in the first page ; mov cx,dx cmp cx,252 jng shrt mov cx,252 ; first page len shrt: mov ax,ds mov bx,es mov ds,bx mov es,ax ; swap them mov bx,dx ; save a copy of data length mvpg: ; start of page move loop sub dx,cx shr cx,1 ; convert to words jnc iseven movsb ; move odd one if needed iseven: rep movsw ; move all words in one page cmp dx,0 ; how many left to move? jng donepg mov cx,dx cmp cx,256 jng shrtr mov cx,256 ; one more page shrtr: mov ax,si ; look at source page cmp ah,STOP_PG jl mvpg mov ah,STRT_PG ; wrap around at this page boundary mov si,ax ; put back in si for rest of packet jmp mvpg donepg: pop ds pop es ; put regs back so ES is shared mem ; ; update the pointer and length in the buffer ; DI already points just past end of data just placed there ; ifdef Microsoft MOV word ptr [_BUFPT],di ; it is here, now MOV AX,word ptr [_BUFBIG] ; total amount of stuff in buffer else MOV word ptr [BUFPT],di ; it is here, now MOV AX,word ptr [BUFBIG] ; total amount of stuff in buffer endif ADD AX,BX ; add in size of this packet INC AX INC AX ; to cover the length value ifdef Microsoft MOV word ptr [_BUFBIG],AX ; after adding in current packet size else MOV word ptr [BUFBIG],AX ; after adding in current packet size endif ; ; ; signs that something is actually happening ; ; push es ; MOV AX,0B000H ; screen ; MOV ES,AX ; MOV DI,3998 ; lower right corner ; INC cs:ICNT ; MOV al,cs:ICNT ; character ; STOSB ; pop es ; ; drop bad frame by forwarding the BNRY register ; or just normal BNRY update after frame read ; fd_bnry: ; drop frm by forward BNRY pop BX ; restore frm ptr in BX add BX, 1 mov AL, ES:[BX] ; next frm start page in AL sub AL, 1 ; new BNRY in AL cmp AL, STRT_PG ; check boundary jge wrbnry mov AL, STOP_PG - 1 wrbnry: wr_wd8 BNRY end_rx: pop es POP BP RET ; for compatibility with other drivers ICNT db 0 ifdef Microsoft _E4RECV ENDP else E4RECV ENDP endif ; ;************************************************************************ ; XMIT ; send a packet to Ethernet ; Is not interrupt driven, just call it when you need it. ; ; usage: xmit(packet,count) ; char *packet; ; int count; ; ; Takes a packet raw, Ethernet packets start with destination address, ; and puts it out onto the wire. Count is the length of packet < 2048 ; ; checks for packets under the Ethernet size limit of 60 and handles them ; ifdef Microsoft _E4XMIT PROC FAR else E4XMIT PROC FAR endif PUSH BP MOV BP,SP push es PUSH DS ; set up proper ds for the buffer ; ; ok, let's hangout here waiting for the transmitter ; mov bx,8000h ; adequate timeout twait: rd_wd8 CMDR ; read up the command reg and al,04h ; xmit flag jz tfree dec bx jnz twait ; keep going till timeout mov ax,-1 ; bummer, it hates me pop ds pop es pop bp ret tfree: cld ; mov al,0c9h wr_wd8 GACFR ; mov ax,WDADD ; shared memory address in ax mov es,ax ; use es for this ; ; move packet into position, set up regs ; MOV AX,[BP+X+2] ; get data ds MOV DS,AX MOV SI,[BP+X] ; DS:SI points to data buffer MOV CX,[BP+X+4] ; count of bytes CMP CX,60 ; minimum length for Ether JNB OKLEN MOV CX,60 ; make sure size at least 60 OKLEN: ; ; Copy Packet : ; ; DS:SI = real data ; ES = shared memory address ; CX = number of bytes ; mov al,0c9h ; reset the gate array wr_wd8 GACFR ; push cx ; save xmit length xor ax,ax mov ah,TSTRT_PG ; starting page number mov di,ax ; ES:DI = shared mem buff start shr cx,1 ; gonna do 16 bits jnc evenx movsb ; pick up odd byte evenx: rep movsw ; copy all data into xmit buf ; mov al,0 wr_wd8 TCR ; ; set up xmit length registers ; pop cx ; len restored in cx pop ds mov al,cl ; length wr_wd8 TBCR0 ; lower byte to TBCR0 mov al,ch wr_wd8 TBCR1 ; higher byte to TBCR1 ; ; set page number ; mov al,TSTRT_PG wr_wd8 TPSR ; write start page into TPSR ; ; issue tx command ; mov al,24h wr_wd8 CMDR ; start xmit ; ; check to see if the last packet xmitted ok ; xor cx,cx ; set a timeout ; waitxmit: ; rd_wd8 CMDR ; command register and al,4 ; xmit bit jz oktogo ; xmit is finished loop waitxmit ; waiting for xmit to complete mov ax,-1 jmp SHORT getout oktogo: xor ax,ax ; ; go back for more ; getout: pop es POP BP RET ifdef Microsoft _E4XMIT ENDP else E4XMIT ENDP endif ; ; ;************************************************************************* ; ETUPDATE ; update pointers and/or restart receiver when read routine has ; already removed the current packet ; ; usage: etupdate(); ; ifdef Microsoft _E4ETUPDATE PROC FAR else E4ETUPDATE PROC FAR endif PUSH ES ifdef Microsoft MOV AX,word ptr [_BUFPT+2] ; establish data segment to buffer else MOV AX,word ptr [BUFPT+2] ; establish data segment to buffer endif MOV ES,AX ; put that in es ; ifdef Microsoft MOV BX,_BUFREAD ; where read pointer is now else MOV BX,BUFREAD ; where read pointer is now endif MOV DX,ES:[BX] ; get size of this packet INC DX INC DX ; two more for length value ADD BX,DX ; increment bufread by size of packet ifdef Microsoft MOV CX,_BUFEND ; right before 2K safety area else MOV CX,BUFEND ; right before 2K safety area endif CMP BX,CX ; see if pointer is over limit JB NOWRAPRD ; we are not at wrap-around ifdef Microsoft MOV BX,_BUFORG ; wrap to here NOWRAPRD: MOV _BUFREAD,BX ; buffer pointer has been updated else MOV BX,BUFORG ; wrap to here NOWRAPRD: MOV BUFREAD,BX ; buffer pointer has been updated endif ; ; DECREMENT TOTAL BUFFER SIZE ; CLI ; keep interrupt handler from bothering dec ifdef Microsoft MOV CX,_BUFBIG ; size before removing packet SUB CX,DX ; remove size of current packet MOV _BUFBIG,CX ; put it back else MOV CX,BUFBIG ; size before removing packet SUB CX,DX ; remove size of current packet MOV BUFBIG,CX ; put it back endif STI ; ; IF RECEIVER IS ON, THEN CHECKING BUFLIM IS UNNECESSARY. ; MOV AL,DEAF ; is the receiver turned off? OR AL,AL ; 0 = reading, 1 = deaf JZ ALIVE ; ; CHECK FOR ROOM IN THE BUFFER, IF THERE IS, TURN ON RECEIVER ; ifdef Microsoft MOV AX,_BUFLIM ; what is our limit? else MOV AX,BUFLIM ; what is our limit? endif CMP CX,AX ; compare to limit JA ALIVE ; not really alive, but can't turn on yet XOR AL,AL MOV DEAF,AL ; reset flag INC OFFS ; keep count how many times this happened ; ; turn receiver back on ; ALIVE: POP ES RET ifdef Microsoft _E4ETUPDATE ENDP else E4ETUPDATE ENDP endif ifdef Microsoft ;_TEXT ends else ENDPS endif END