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147 lines
4.7 KiB

; slip.asm
;
; This is an 8086+ implementation of SLIP (RFC 1055)
;
; It may be assembled using Microsoft's MASM using the command line:
; ml -Fl -c slip.asm
;
; or using Borland's TASM using the command line:
; tasm -la -m2 -jLOCALS slip.asm
;
.model small
.stack 100h
.data
SLIP_END equ 0C0h
SLIP_ESC equ 0DBh
SLIP_ESC_END equ 0DCh
SLIP_ESC_ESC equ 0DDh
; note that these are both sample macros and are very simple
; In both cases, DX is assumed to already be pointing to the
; appropriate I/O port and a character is always assumed to
; be ready.
SEND_CHAR macro char
IFDIFI <char>, <al>
mov al,char
ENDIF
out dx,al
endm
RECV_CHAR macro
in al,dx
endm
.code
;****************************************************************************
; send_packet
;
; sends the passed packet (which is in a memory buffer) to the output
; device by using the macro SEND_CHAR() which must be defined by the
; user. A sample SEND_CHAR() is defined above.
;
; Entry:
; DS:SI ==> raw packet to be sent
; CX = length of raw packet to be sent
; direction flag is assumed to be cleared (incrementing)
;
; Exit:
;
;
; Trashed:
; none
;
;****************************************************************************
send_packet proc
push cx
push si
SEND_CHAR SLIP_END ; send an end char to flush any garbage
jcxz @@bailout ; if zero length packet, bail out now
@@nextchar:
lodsb ; load next char
cmp al,SLIP_END ; Q: is it the special END char?
jne @@check_esc ; N: check for ESC
SEND_CHAR SLIP_ESC ; Y: send ESC + ESC_END instead
mov al,SLIP_ESC_END ;
jmp @@ordinary ;
@@check_esc:
cmp al,SLIP_ESC ; Q: is it the special ESC char?
jne @@ordinary ; N: send ordinary char
SEND_CHAR SLIP_ESC ; Y: send ESC + ESC_END instead
mov al,SLIP_ESC_ESC ;
; fall through to ordinary character
@@ordinary:
SEND_CHAR al ;
loop @@nextchar ; keep going until we've sent all chars
@@bailout:
SEND_CHAR SLIP_END ; send an end char to signal end of packet
pop si
pop cx
ret
send_packet endp
;****************************************************************************
; recv_packet
;
; receives a packet using the macro RECV_CHAR() which must be defined by
; the user and places the received packet into the memory buffer pointed
; to by ES:DI. The final length is returned in BX.
;
; Note that in the case of a buffer overrun, the portion of the packet
; that fit into the buffer is returned and BX and CX are equal. There
; is no way to tell the difference between a packet that just exactly
; fit and one which was truncated due to buffer overrun, so it is
; important to assure that the buffer is big enough to ALWAYS contain
; at least one spare byte.
;
; A sample RECV_CHAR() is defined above.
;
; Entry:
; ES:DI ==> packet buffer
; CX = length of buffer
; direction flag is assumed to be cleared (incrementing)
;
; Exit:
; BX = length of packet received
;
; Trashed:
; none
;
;****************************************************************************
recv_packet proc
push cx
push di
xor bx,bx ; zero received byte count
jcxz @@bailout ; if zero length packet, bail out now
@@nextchar:
RECV_CHAR ; fetch a character into al
cmp al,SLIP_END ; Q: is it the special END char?
jne @@check_esc ; N: check for ESC
or bx,bx ; YQ: is it the beginning of packet?
jz @@nextchar ; Y: keep looking
jmp @@bailout ; N: end of packet, so return it
@@check_esc:
cmp al,SLIP_ESC ; Q: is it the special ESC char?
jne @@ordinary ; N: it's an ordinary char
RECV_CHAR ; Y: get another character
cmp al,SLIP_ESC_END ; Q: is it ESC_END?
jne @@check_esc_esc ; N: check for ESC_ESC
mov al,SLIP_END ; Y: convert to ordinary END char
jmp @@ordinary ;
@@check_esc_esc:
cmp al,SLIP_ESC_ESC ; Q: is it ESC_ESC?
mov al,SLIP_ESC ; Y: convert to ordinary ESC char
; protocol violation! fall through to ordinary character
@@ordinary:
stosb ; store character in buffer
inc bx ; got another char
loop @@nextchar ; keep going until we've sent all chars
@@bailout:
pop di
pop cx
ret
recv_packet endp
END