asmpkt2.s

开放源码的编译器open watcom 1.6.0版的源代码

;
; Packet-driver receiver upcall handler. This module is only
; used by small/large real-mode targets assembled with NASM.
;
; This file requires NASM 0.98+ to assemble.
;

[GLOBAL _pkt_receiver_rm]
[EXTERN _pkt_enque_ptr]

%define  PKTBUF_SIZE 1514
%idefine offset

rx_buf_ptr  equ $
            dw rx_buf, SEG rx_buf
nullPtr     dd 0

rx_buf      resb (PKTBUF_SIZE)  ; receive buffer
rx_len      dw 0

rx_stk      resw (64)           ; a small work stack
rx_stk_end  equ $
            dw 0

_pkt_receiver_rm:
        pushf
        cli                        ; no interruptions now
        or   al, al                ; AL = 0 if 1st call from pkt-driver
        jnz  @enque                ; AL <>0, 2nd call; enqueue packet

        cmp  cx, PKTBUF_SIZE       ; check the packet length
        ja   @no_fnd               ; pretend none were found
        les  di, [cs:rx_buf_ptr]
        mov  [cs:rx_len], cx       ; save buffer len for pkt_enqueue
        popf
        retf

@no_fnd:les  di, [cs:nullPtr]      ; return NULL ptr
        popf
        retf

        ;
        ; enque packet, DS:SI=ES:DI from 1st call, i.e. DS=CS
        ;
@enque: cmp  si, offset rx_buf
        jne  @exit                 ; not a valid pointer, don't enqueue

        mov  ax, SEG rx_buf
        mov  ds, ax                ; load our DS
      ;
      ; Watcom assumes SS=DS in pkt_enqueue(). We therefore
      ; need to setup a new work-stack.
      ;
        mov  cx, ss
        mov  dx, sp
        mov  ss, ax                ; setup new stack (SS=DS)
        lea  sp, [rx_stk_end]
        push cx                    ; save SS on new stack
        push dx                    ; save SP on new stack

        cld                        ; C-code assumes forward direction
        push bx                    ; store handle, length and buf address
        push word [cs:rx_len]
        push cs
        push si
        call far [_pkt_enque_ptr]
        add  sp, 8

        pop  dx                    ; restore old stack
        pop  cx
        mov  ss, cx
        mov  sp, dx

@exit:  popf
        retf

END