; ; Low level ASYNC serial I/O driver for ; use with DDS MICRO-C compiler on IBM/PC. ; ; Copyright 1990-2000 Dave Dunfield ; All rights reserved. ; ; Misc constants. ?BUFMSK EQU $00FF ;Buffer size mask ?WINDOW EQU 256-30 ;Flow control assertion window ?RXRDY EQU %00000001 ;Uart Receiver ready flag ?TXRDY EQU %00100000 ;Uart Transmitter ready flag ?8259 EQU $0020 ;8259 interrupt controller ; Bits in driver control flags ?RFLOW EQU %10000000 ;Received flow control ?TFLOW EQU %01000000 ;Transmit flow control ?TXOFF EQU %00100000 ;Transmit XOFF pending ?TXON EQU %00010000 ;Transmit XON pending ?XPAREN EQU %00001000 ;Transparency enabled ; $SE:1 ; ; Initialized variables & tables ; Cflags DB 0 ;Control flags ?comvec DW 0 ;Comm interrupt vector ; $DD:?rdptr 2 ;Buffer read pointer $DD:?wrptr 2 ;Buffer write pointer $DD:?comadr 2 ;Com port address $DD:?oldoff 2 ;Saved old interrupt offset $DD:?oldseg 2 ;Saved old interrupt segment $DD:?buffer 256 ;Receive buffer ; $SE:0 ; ; Open the com port: Copen(int port, int speed, char mode, char modem) ; Copen PUSH BP ;Save callers stack MOV BP,SP ;Address parameters CALL Cclose ;Insure its closed MOV AX,10[BP] ;Get com port MOV DX,#$03FD ;Comm 1 address MOV BX,#$0030 ;Comm 1 interrupt vector MOV CL,#$0EF ;Comm 1 interrupt mask DEC AX ;Is it com1? JZ ?2 ;Yes, it is MOV DX,#$02FD ;Comm 2 address MOV BX,#$002C ;Comm 2 interrupt vector MOV CL,#$0F7 ;Comm 2 interrupt mask DEC AX ;Is it com2? JZ ?2 ;Yes it is ; Report failure to open port ?1 STI ;Insure interrupts enabled MOV AX,#-1 ;Indicate failure POP BP ;Restore caller RET ; Proceed with opening the comm port ?2 MOV ?comadr,DX ;Save address CLI ;Inhibit interrupts ; Setup the uart DEC DX ;Backup ... DEC DX ;to line control register (FB) IN AL,DX ;Read current value OR AL,#$80 ;Enable baud rate register OUT DX,AL ;Write it MOV AX,8[BP] ;Get baud rate SUB DX,#3 ;Point to baud rate LSB (F8) OUT DX,AL ;Write it INC DX ;Advance to MSB (F9) MOV AL,AH ;Get MSB OUT DX,AL ;Write it DEC DX ;Backup to LSB (F8) IN AL,DX ;Re-read LSB MOV AH,AL ;Copy for later INC DX ;Back to MSB (F9) IN AL,DX ;Re-read MSB XCHG AH,AL ;Swap for multi CMP AX,8[BP] ;Does it match JNZ ?1 ;No, its dosn't MOV AL,6[BP] ;Get mode AND AL,#$7F ;Insure no baud rate INC DX ;Advance... INC DX ;to line control register (FB) OUT DX,AL ;Write it MOV AL,#$01 ;Receive interrupt only DEC DX ;Backup ... DEC DX ;to Interrupt enable register (F9) OUT DX,AL ;Write it MOV AL,4[BP] ;Get modem control ADD DX,#3 ;Point to modem control register (FC) OUT DX,AL ;Write it ; Setup the interrupt vector MOV ?comvec,BX ;Save interrupt vector MOV CS:?dsval,DS ;Save data segment for int handler XOR AX,AX ;Get a zero MOV ?rdptr,AX ;Zero read pointer MOV ?wrptr,AX ;Zero write pointer MOV AX,ES:[BX] ;Get old offset MOV ?oldoff,AX ;Save old offset MOV AX,ES:2[BX] ;Get old segmemt MOV ?oldseg,AX ;Save segment MOV AX,#?COMINT ;Point to routine MOV ES:[BX],AX ;Write new offset MOV ES:2[BX],CS ;Write new segment ; Clear out any pending characters SUB DX,#4 ;Point to data register (F8) IN AL,DX ;Read to clear interrupt IN AL,DX ;Read to clear interrupt ; Setup the interrupt controller IN AL,?8259+1 ;Read interrupt mask AND AL,CL ;Enable serial port OUT ?8259+1,AL ;Write interrupt controller STI ;Re-enable interrupts XOR AX,AX ;Indicate success POP BP ;Restore caller RET ; ; Close the comm port: Cclose() ; Cclose XOR AX,AX ;Get zero MOV ES,AX ;Point to interrupt vectors MOV BX,?comvec ;Get old vector AND BX,BX ;Is it set? JZ ?3 ;No, its not MOV ?comvec,AX ;Indicate not set CLI ;Disable interrupts ; Restore the old comm interrupt vector MOV DX,?oldoff ;Get old offset MOV ES:[BX],DX ;Restore old offset MOV DX,?oldseg ;Get old segment MOV ES:2[BX],DX ;Restore old segment ; Disable interrupts on the uart MOV DX,?comadr ;Get uart address SUB DX,#4 ;Point to interrupt enable register OUT DX,AL ;Write zero IN AL,?8259+1 ;Read interrupt mask OR AL,#$18 ;Disable comm interrupts OUT ?8259+1,AL ;Write interrupt mask STI ;Re-enable interrupts ?3 RET ; ; Test for char from com port: int Ctestc() ; Ctestc MOV BX,?rdptr ;Get read pointer CMP BX,?wrptr ;Test for data in buffer JNZ ?4 ;Yes, we have some MOV AX,#-1 ;Report no data available RET ; ; Read a character from the comport: int Cgetc() ; Cgetc MOV BX,?rdptr ;Get read pointer CMP BX,?wrptr ;Test for data in buffer JZ Cgetc ;No characters, wait for them ; Read character from com port ?4 MOV DI,#?buffer ;Get I/O buffer address MOV AL,[BX+DI] ;Get character from buffer XOR AH,AH ;Zero high INC BX ;Advance read pointer AND BX,#?BUFMSK ;Mask for buffer wrap MOV ?rdptr,BX ;Resave read pointer CMP BX,?wrptr ;Did we just empty buffer? JNZ ?3 ;No, its ok PUSH AX ;Save for later ; Buffer is empty, send XON if necessary MOV DX,?comadr ;Point to com port CLI ;No interrupts MOV AH,Cflags ;Get control flags TEST AH,#?TFLOW ;Flow controlled? JZ ?7 ;No, its not AND AH,#~(?TFLOW|?TXOFF|?TXON) ;Clear flags IN AL,DX ;Get status TEST AL,#?TXRDY ;Ok to send? JZ ?5 ;No, set pending SUB DX,#5 ;Backup to data port MOV AL,#'Q'-$40 ;Get XON character OUT DX,AL ;Send the XON JMP <?6 ;And continue ; Cannot send not, set pending flag ?5 OR AH,#?TXON ;Set XON pending flag ?6 MOV Cflags,AH ;Resave the flags ?7 STI ;Re-enable interrupts POP AX ;Restore character RET ; ; Write a character to the com port: Cputc(char c) ; Cputc PUSH BP ;Save callers stack frame MOV BP,SP ;Address parameters ?8 MOV DX,?comadr ;Get address of uart IN AL,DX ;Read uart status TEST AL,#?TXRDY ;Ok to transmit JZ ?8 ;No, wait for it SUB DX,#5 ;Position to data address CLI ;Disallow interrupts MOV AH,Cflags ;Get control flags ; Test for pending XOFF to send TEST AH,#?TXOFF ;Transmit XOFF? JZ ?9 ;No, try next MOV AL,#'S'-$40 ;Get XOFF AND AH,#~?TXOFF ;Clear the bit JMP <?10 ;Write to comm port ; Test for pending XON to send ?9 TEST AH,#?TXON ;Transmit XON? JZ ?11 ;No, output character MOV AL,#'Q'-$40 ;Get XON AND AH,#~?TXON ;Clear the bit ; Resave the control flags & proceed ?10 MOV Cflags,AH ;Re-save control flags STI ;Re-enable interrupts OUT DX,AL ;Write character JMP <?8 ;And proceed ; No pending flow control, output data ?11 STI ;Re-enable interrupts TEST AH,#?RFLOW ;Output inhibited? JNZ ?8 ;Yes, wait for it MOV AL,4[BP] ;Get character OUT DX,AL ;Write to comm port POP BP ;Restore caller RET ; ; Read the com port signals: int Csignals() ; Csignals MOV DX,?comadr ;Get the com port address INC DX ;Advance to modem status register IN AL,DX ;Read modem status XOR AH,AH ;Zero high bits RET ; ; Comms Interrupt handler ; ?COMINT PUSH AX ;Save AX PUSH BX ;Save BX PUSH DX ;Save DX PUSH DI ;Save DI PUSH DS ;Save DS MOV DS,CS:?dsval ;Get data segment MOV DX,?comadr ;Get com port I/O address IN AL,DX ;Read uart status register TEST AL,#?RXRDY ;Receiver ready? JZ ?15 ;No, Spurious interrupt SUB DX,#5 ;Backup to data port MOV AH,Cflags ;Get comm flags IN AL,DX ;Read data character TEST AH,#?XPAREN ;Are we transparent? JNZ ?13 ;Yes, do not interpret flow control ; Test for XOFF, inhibit output CMP AL,#'S'-$40 ;Is it XOFF? JNZ ?12 ;No, try next OR AH,#?RFLOW ;Set flow control bit JMP <?14 ;and continue ; Test for XON, enable output ?12 CMP AL,#'Q'-$40 ;Is it XON JNZ ?13 ;No, its not AND AH,#~?RFLOW ;Reset flow control bit JMP <?14 ;and continue ; Normal character, stuff in buffer ?13 MOV DI,#?buffer ;Get I/O buffer address MOV BX,?wrptr ;Get write pointer MOV [BX+DI],AL ;Write into buffer INC BX ;Advance AND BX,#?BUFMSK ;Mask for buffer wrap MOV ?wrptr,BX ;Resave pointer ; Test for nearing end of buffer SUB BX,?rdptr ;Calculate size of buffer AND BX,#?BUFMSK ;Mask for buffer wrap CMP BX,#?WINDOW ;Are we nearing end JB ?15 ;No, its ok TEST AH,#?XPAREN ;Are we transparent? JNZ ?15 ;Don't send flow ctrl ; Send XOFF, flow control dest OR AH,(?TFLOW|?TXOFF) ;Indicate flow control asserted AND AH,#~?TXON ;Insure no XON pending ADD DX,#5 ;Offset to status register IN AL,DX ;Read status TEST AL,#?TXRDY ;Test for transmitter ready JZ ?14 ;Not ready SUB DX,#5 ;Backup to data port MOV AL,#'S'-$40 ;Get XOFF character OUT DX,AL ;Write to port AND AH,#~?TXOFF ;No pending XOFF needed ; Resave status flags to record ;changes ?14 MOV Cflags,AH ;Resave flags ; Reset 8259, Restore registers ;& return from interrupt ?15 MOV AL,#$20 ;End of Interrupt command OUT ?8259,AL ;Write to interrupt controller POP DS ;Restore DS POP DI ;Restore DI POP DX ;Restore DX POP BX ;Restore BX POP AX ;Restore AX IRET ; Saved data segment incase we are running in small model ?dsval DW 0 ;Stored code segment value D
file: /Techref/com/dunfield/ftp/embedpc/comm_asm.htm, 28KB, , updated: 2000/5/5 09:49, local time: 2024/12/23 06:48,
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