; 8530 general-purpose control subroutines
; Copyright 1991 Phil Karn, KA9Q
;%    .MODEL  MEMMOD,C
include asmgloba.h        
	LOCALS
	%MACS
	.LALL
	
	.DATA

	.CODE
; Write a 8530 register. Called from C as
; write_scc(int ctl,char reg,char val);
	public  write_scc
write_scc       proc
	arg     ctl:word,reg:byte,val:byte
	pushf
	mov     dx,ctl
	mov     al,reg
	cmp     al,0
	jz      @@doit          ; no need to set register 0
	cli
	out     dx,al
; Allow enough delay for 16 MHz 80386 and a 4.9152 MHz 8530
; The delay uses a NOP in a loop because of the pipeline in the 80386.
; The loop instruction causes the 80386 to flush the pipeline and reload.
; The 8530 requires a delay of 6 PCLK + 200 ns - a loop of 8 should be
; adequate to a 16 Mhz 80386.
	mov     cx,8
@@w1:   nop
	loop    @@w1
@@doit: mov     al,val
	out     dx,al
	popf
	ret
write_scc       endp

; Read a 8530 register. Called from C as
; read_scc(int ctl,char reg);
	public  read_scc
read_scc        proc
	arg     ctl:word,reg:byte
	pushf
	mov     dx,ctl
	mov     al,reg
	cmp     al,0
	jz      @@doit  ; no need to set reg if R0
	cli
	out     dx,al
; allow enough delay for the 8530 to settle (see comments above)
	mov     cx,8
@@r1:   nop
	loop    @@r1
@@doit: in      al,dx
	mov     ah,0
	popf
	ret
read_scc        endp

; Read packets from the 8530 receiver.
; Returns when either a good frame is received, or when carrier drops.
; If a good frame is received, the length is returned; otherwise -1.
	public  rx8530
rx8530  proc
	arg     ctl:word,data:word,buf:ptr,bufsize:word 
	uses    di

@@restart:
	if      @Datasize NE 0
		les     di,buf
	else
		mov     di,buf  ; cp = buf
		mov     ax,ds
		mov     es,ax
	endif

	cld
	mov     cx,0            ; cnt = 0
@@rxloop:
	mov     dx,ctl  ; read status
	in      al,dx           ; into al
	test    al,08h          ; DCD still present?
	jz      @@dcdoff        ; nope, quit
	test    al,080h         ; Abort?
	jnz     @@restart       ; yes, start again
	test    al,01h          ; character available?
	jz      @@nochar        ; nope, go on
	mov     dx,data
	in      al,dx           ; get it
	stosb                   ; and stash: *cp++ = char
	inc     cx              ; cnt++
	cmp     cx,bufsize      ; cx == bufsize?
	jnz     @@rxloop

	mov     dx,ctl  ; buffer overflowed; abort receiver
	mov     al,3            ; select register 3
	out     dx,al
	mov     al,0d9h         ; ENT_HM|RxENABLE|RxCRC_ENAB|Rx8
	nop
	nop
	nop
	nop
	nop
	out     dx,al
	jmp     @@restart
@@nochar:
	mov     al,1            ; Select error register (R1)
	mov     dx,ctl
	out     dx,al
	nop
	nop
	nop
	nop
	nop
	nop
	in      al,dx           ; read error reg (R1)
	test    al,080h         ; end of frame?
	jz      @@rxloop        ; nope, keep looking

	test    al,040h         ; End of frame. CRC error?
	jnz     @@restart       ; yup; start again
	mov     ax,cx           ; good frame; return with count
	ret

@@dcdoff:
	mov     ax,0ffffh       ; DCD dropped, return -1
	ret

rx8530  endp
	end

