exxos's Atari, Amiga & retro forum

Code: Select all

;***
;
; ipc_write_bit - Write a bit to the IPC with timeout.
;
; d0.b	-	Bit to be written in bit 0.
; d1.w	-	Timeout in number of retries reading the status bit.
;		(Must be given)
;
; Returned values.
;
; d1.w	-	Zero if timeout error otherwise undefined.
;
;***

ipc_write_bit:
	movem.l	d2-d7/a0-a6,-(SP)

	lea	zx83_w_ipcwreg,a0	; Load the ZX8302 registers into a0 and a1
	lea	zx83_r_cstatus,a1

	rol.b	#1,d0			; Move the data bit to be bit 1
	or.b	#%00001100,d0		; Or it with the rest of the required register content.

	move.b	d0,(a0)			; Write it to the IPC Write register.

ipc_write_bit_loop1:			; Loop around checking the status bit (6)
	move.b	(a1),d3
	btst	#6,d3
	dbeq	d1,ipc_write_bit_loop1	; If it's not set then go around d1.w + 1 times.

	addi.w	#1,d1			; Add 1 to d1. If the loop has completed then this will be -1
					; We need it to be 0 as an error condition.

	movem.l	(SP)+,d2-d7/a0-a6
	rts

;***
;
; ipc_read_bit	- Read a bit from the IPC with timeout.
;
; Parameters
;
; d1.w	-	Timeout in number of retries reading the status register.
;		(Must be given)
; Returns
;
; d0.b	-	Bit returned in bit 0 of the byte.
; d1.w	-	Timed out if 0 otherwise undefined.
;
;***

ipc_read_bit:
	movem.l	d2-d7/a0-a6,-(SP)

	lea	zx83_r_cstatus,a0	; Load the address of the communication status register into a0

ipc_read_bit_loop1:
	move.b	(a0),d2			; Get the contents of the communications status register into d2
	btst	#6,d2			; Is the IPC acknowledge bit set?
	dbeq	d1,ipc_read_bit_loop1	; No? If d1 is > -1 go around again.

	addi.w	#1,d1			; If the timeout failed then d1 will be -1, so add 1.

	andi.b	#%1000000,d2		; Mask off all the bits we're not interested in.
	ror.b	#7,d2			; Move it to bit 0
	move.b	d2,d0			; Copy it to d0

	movem.l	(SP)+,d2-d7/a0-a6
	rts