;
; 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: 2025/2/5 11:11,
|
| | ©2025 These pages are served without commercial sponsorship. (No popup ads, etc...).Bandwidth abuse increases hosting cost forcing sponsorship or shutdown. This server aggressively defends against automated copying for any reason including offline viewing, duplication, etc... Please respect this requirement and DO NOT RIP THIS SITE. Questions?
<A HREF="http://linistepper.com/Techref/com/dunfield/ftp/embedpc/comm_asm.htm"> Comm.asm </A> |
| Did you find what you needed?
|