implement the rest of iec_rx_byte

c64/kernal/iec_rx_byte.s

@@ -9,19 +9,77 @@ iec_rx_byte:
 	jsr iec_wait_for_clock_release
 
 	;; We then release the data line
+	;; (We can use this routine, since we weren't holding CLK, anyway)
+	jsr iec_release_clk_and_data
 
 	;; Wait for talker to assert CLK.
 	;; If >200usec, then it is EOI and we have to assert the
 	;; DATA line for 60 usec to tell the TALKER that we have
 	;; acknowledged the EOI.
+	ldx #20
+iec_rx_clk_wait:
+	;; Loop takes 11 usec, so ~20 iterations for 200usec timeout
+	lda $dd00
+	bpl +
+	dex
+	bpl iec_rx_clk_wait
 
+	;; EOI timeout: So pulse DATA line for 60 usec
+	jsr iec_assert_data
+	jsr iec_wait60us
+	jsr iec_release_clk_and_data
 
+	;; Assert some kind of flag so that we know if it was EOI = the last byte on offer
+	
+	;; And still wait for CLK to be asserted
+	;; XXX - This will cause periodic EOI pulses if the sender takes too long.
+	;; That is probably ok.
+	ldx #$7f
+	jmp iec_rx_clk_wait
+
+*
 	;; CLK is now low.  Latch input bits in on rising edge
 	;; of CLK, eight times for eight bits.
+	ldx #7
+
+	lda #$00
+	php
+	
+iec_rx_bit_loop:	
+	;; Wait for CLK to release
+	jsr iec_wait_for_clock_release
+	;; DATA now has the next bit, but inverted.
+	;; DATA is in bit6, which is a bit annoying.
+	;; But we can clock it out with two ROL instructions
+	;; so that it is in C. We can then ROL it into the
+	;; partial data byte
+	;; Move data bit into C flag
+	LDA $DD00
+	ROL
+	ROL
+	;; Pull it into the data byte
+	pla
+	ROL
+	eor #$01  		; Invert the data bit
+	pha
+
+	;; Wait for CLK to re-assert
+	jsr iec_wait_for_clock_assert
+
+	;; More bits?
+	dex
+	bpl iec_rx_bit_loop
 
 	;; Then we must within 1000usec acknowledge the frame by
 	;; asserting DATA. At this point, CLK is asserted by the
 	;; talker and DATA by us, i.e., we are ready to receive
 	;; the next byte. (p11).
+	jsr iec_assert_data
 
+	;; Retreive the received byte
+	PLA
+
+	;; Return no-error
+	CLC
+	RTS
 	

c64/kernal/iec_wait_for_clock_assert.s

@@ -0,0 +1,5 @@
+iec_wait_for_clock_assert:
+	LDA $DD00
+	and #$80
+	bne iec_wait_for_clock_assert
+	rts