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Assembly Source File | 1985-11-06 | 16.6 KB | 386 lines

PAGE 66,132 TITLE HOST - Link communication device to console using interrupts ; ; Program to install resident communications interrupt driver, ; and link it into the keyboard/video interrupt routines. ; ; We must define a general interrupt handler for the COM1 port, ; which will input characters directly into BIOS's keyboard input ; (typeahead) buffer. This buffer is defined by pointers at offset ; 001A (start of buffer pointer), and 001C (end of buffer pointer). ; The data segment for all of this is 0040. There is a BIOS routine ; at F000:E875 which handles a 15-char circular buffer wrap-around. ; We should copy it. We must compare [001A] with [001C] after calling ; the buffer wrap routine to see if the buffer full. If so, it'd ; be nice to send a bell to the caller, but im not sure this is the ; place to do it (inside an interrupt routine). ; ; Note that we assume the COM1 port is already initialized (RS232 stuff) ; ; Note that this routine must also detect change of line status and ; have appropriate logic for indicating and handling loss of carrier, ; and other delta indications in the line status register. ; ; This takes care of the keyboard input end of the communication ; interface. ; ; For linking screen output, I guess we just intercept the old ; screen output 'interrupt' vector, located at 0000:0040-:0043. ; There is no reason to buffer the output, so the intercept routine ; will first output the byte to the UART (if UART accepting), then ; pass control on to the former screen handler. ; ; The record-type HOSTFLAGS contains duplex, CR/LF, bell enable, and ; timeout specification. Timeout determines iff forced disconnect for ; lack of user input enablad. hostflags record duplex:1,crlf:1,bell:1,cls:1,timeout:1 discflags record rlsd:1,ri:1,dsr:1,cts:1 ; comment % ; Structure HOSTCB contains terminal setting values: hostcb struc clsequence db 0,12 ; default cls sequence timeout_at db 128 ; halfway through the timeout scale default baudrate_lsb db 80h baudrate_msb db 1 ; default UART baud rate = 300 baud userid dt ? ; ten bytes? for user identification screen_size db 24 ; # of lines on screen screen_width db 80 ; # of chars per line on screen hostcb ends ; % ; inport macro port lea dx,port ; get port offset into dx in al,dx endm ; outport macro port lea dx,port ; get port offset into dx out dx,al endm ; ; Set up references to the system interrupt vector table: ; ; int_table segment at 0h org 10H*4 ; address of video driver vector int10 label word org 0CH*4 ; address of comm interrupt vector int0c label word int_table ends ; ; Set up references to BIOS keyboard and COM system table. ; ; sys_table segment at 40h rs232_base dw 4 dup(?) org 1Ah buffer_head dw ? buffer_tail dw ? kb_buffer dw 16 dup(?) kb_buffer_end label word org 71h bios_break db ? sys_table ends ; ; comgrp group host,com_init ; host segment assume cs:comgrp ; ; Proc to bump BIOS's keyboard buffer pointer, in DI. advance_kb proc far add di,2 cmp di,offset kb_buffer_end jnz noneed mov di,offset kb_buffer ; wrap if at end of buffer noneed: ret advance_kb endp ; eoi equ 20h ; end of interrupt value for 8259 controller ; baud_data equ 0[BX] ; baud rate selector and data register in UART baud_msb_int equ 1[BX] ; baud rate selector MSB and interrupt enable interrupt_id equ 2[BX] ; interrupt identification register line_control equ 3[BX] ; line control register modem_control equ 4[BX] ; modem control register line_status equ 5[BX] ; line status register modem_status equ 6[BX] ; modem status register ; comint proc far assume cs:comgrp,ds:sys_table sti push ax push bx push cx push dx push si push di push ds push es mov ax,sys_table ; point to system table segment mov ds,ax mov bx,rs232_base ; get base port for COM1 device ; ; Begin code to interrogate interrupt situation: "Why were we called ?" ; ; Note that we have set interrupts for change in modem status, and ; receiver data-ready. This means either he hung up (or ?) or he ; just sent us a character. The interrupt-id register will tell us which. ; inport interrupt_id ; read the interrupt id register shr al,1 ; of course an interrupt occurred! and al,00000011b ; lower 2 bits active. jz delta_stat ; go interpret change in modm stat dec al ; test for transmitter hold empty. jz no_action ; we're not processing these here. dec al ; test for received char? jz get_com_char ; read char from com device. dec al ; Break or error received. jz brk_rcd no_action: mov al,eoi ; end-of-inerrupt code to al out 20h,al ; tell controller to cancel interrupt pop es pop ds pop di pop si pop dx pop cx pop bx pop ax iret ; return to previous task. ; ; Break was received (or there was a line error) ; IF break received, simulate console CONTROL-BREAK function. ; brk_rcd: inport line_status and al,00010000b ; break detected ? jz no_action ; we're ignoring other errors now. mov di,offset kb_buffer ; load kb_buffer start mov buffer_head,di ; reset buffer to empty mov buffer_tail,di mov bios_break,80h ; set break byte. int 1bh ; do break service jmp no_action ; return ourselves ; get_com_char: inport baud_data ; read byte from port mov di,buffer_tail ; end of kb buff mov si,di ; store it call advance_kb ; try to make space for it cmp di,buffer_head ; has buffer wrapped ? jz kb_full ; buffer full! xor ah,ah ; convert al -> ax mov [si],ax ; store it in BIOS keyboard buffer mov buffer_tail,di ; update buffer jmp no_action ; return to caller ; kb_full: jmp no_action ; we'll eventually BEEP the user here. ; delta_stat: inport modem_status mov cs:c_modem_status,al ; remember new modem status jmp no_action ; comint endp ; ; console_out proc far assume cs:host,ds:sys_table jmp begin_console ; jump around ID field console_id: db 'HOST' ; our identification field begin_console: cmp ah,14 ; is it 'print tty' function ? jz take_over ; yes, intercept it cmp ah,10 ; it is 'print over char' function ? jz take_over ; yes, lets intercept it too normal_tty: jmp cs:old_int10 ; go to normal int 10 handler take_over: push ax push di push si push dx push bx push cx push ds test cs:c_modem_status,10000000b ; is there a connection? jz bypass_user ; no, we wont try to send mov cl,al ; save value for output mov ax,sys_table mov ds,ax ; prepare to examine UART mov bx,rs232_base ; get base address of com port send_char: inport line_status ; see if ready to send byte. and al,00100000b ; test xmit hold reg empty ? jz send_char ; no, wait for it mov al,cl ; get back char to send outport baud_data ; output byte to com1 iff ready bypass_user: pop ds pop cx pop bx pop dx pop si pop di pop ax jmp normal_tty ; console_out endp ; old_int10 dd ? ; doubleword pointer to old int10 ; ; Set up our internal status flags: c_modem_status discflags <?,?,?,?> ; Set up user parm area user_flags hostflags <1,1,1,1,1> ; user logon and termninal flags user_disc discflags <1,0,1,0> ; lines for continual test/disconnect ;user_parms hostcb <,,,,,,> ; user logon and terminal characteristics user_parms equ $ ; ; Structure HOSTCB contains terminal setting values: clsequence db 0,12 ; default cls sequence timeout_at db 128 ; halfway through the timeout scale default baudrate_lsb db 80h baudrate_msb db 1 ; default UART baud rate = 300 baud userid dt ? ; ten bytes? for user identification screen_size db 24 ; # of lines on screen screen_width db 80 ; # of chars per line on screen ; end_com equ this byte ; return to dos, stay res. ; host ends ; com_init segment assume cs:com_init,ds:sys_table,es:comgrp host_init proc far ; ; We'll assume that the UART has been initialized for now ; we will install the interrupt driven keyboard link and ; the INT 10H intercept driver. ; cli ; off ints so dont get caught push ds ; save pointer to dos psp mov ax,50h ; offset to int21 in psp push ax mov ax,host ; point to driver segment mov es,ax mov ax,sys_table ; point to system table mov ds,ax mov bx,rs232_base ; get base of port addresses inport modem_status mov es:c_modem_status,al ; initialize out record of it mov al,00001011b ; set MCR for interrupts outport modem_control mov al,00001101b ; desired interrupt fields outport baud_msb_int ; enable those interrupts mov ax,int_table ; get interrupt table segment mov ds,ax assume ds:int_table mov dx,int10 ; get offset for old int10 push dx push bx push ds xchg bx,dx ; put offset into bx mov ax,host ; address ID field mov ds,ax mov dx,[bx+3] ; look at our ID field1 cmp dx,'HO' ; Could it be us ? jnz notus ; nop. mov dx,[bx+5] ; Look at field 2 to be sure cmp dx,'ST' notus: pop ds pop bx pop dx jnz itsok jmp reject_init ; We were already installed itsok: mov es:old_int10,dx ; fill in mov dx,int10+2 ; get segment for old int10 mov es:old_int10+2,dx ; fill in mov dx,host ; get new seg for int10 mov int10+2,dx ; store it mov dx,offset console_out ; get new offset for int10 mov int10,dx ; store it mov dx,host ; get new seg for int0c mov int0c+2,dx ; store it mov dx,offset comint ; and offset mov int0c,dx ; and offset in al,21h ; read from IMR and al,0efh ; turn off b4=enable comm interrupts out 21h,al ; in 8259 controller mov al,0 ; retcode = 0 mov dx,offset comgrp:end_com; point to end of program mov cl,4 ; for devide by 16 shr dx,cl ; turn into # segments add dx,100 ; leave 1K for dos environ ???? mov ah,31h ; tell DOS to save this pgm. jmp ok_init ; successful initialization ; exit_init: ret ; far ret to dos function call ; ok_init: sti ; re-enable the interrupts ; call print_inline ; db 'pcHOST 1.0 - 09/29/83 - M.R.',13,10 ; db 'Communication console link loaded and initialized.' ; db 13,10,10,0 jmp exit_init ; reject_init: sti ; re-enable the interrupts ; call print_inline ; db 'HOST driver is already installed.',13,10 ; db 'Nothing done.',13,10,0 ; pop ax ; pop off 'stay resident' return ; xor ax,ax ; make 'terminate overlay' return ; push ax jmp exit_init ; ; Print_Inline proc: Prints ASCIIZ text at offset on NEAR STACK. ; Returns to address following delimiting zero of ASCIIZ string. ; Resgisters destroyed: SI. print_inline proc pop si push ax check_char: mov al,[si] inc si or al,al jz msg_done call print_chr jmp check_char msg_done: pop ax ; get back ax push si ; is this the ONLY way to jump ret ; to an address pointed to by SI ? print_inline endp ; ; Print_Chr proc: prints char in AL via INT 10H. ; Registers destroyed: AX. print_chr proc mov ah,14 ; and AH for PRINT TTY function call int_10h ; print char to tty ret print_chr endp ; ; INT_10H proc: Intercept to the BIOS INT 10H ; but saving all registers. Also, set BX=0 to select current ; screen page. All registers except BX must be set prior call. ; Registers destroyed: None. int_10h proc push bx push ax mov bx,0 ; select screen zero push bp push di push si int 10h pop si pop di pop bp pop ax pop bx ret int_10h endp ; host_init endp com_init ends ; ; end host_init