IEC code compatibility improvements

c64/kernal/iec/iec_rx_byte.s

@@ -13,7 +13,9 @@ iec_rx_byte:
 	pha
 
 	// Timing is critical here - execute on disabled IRQs
-	php
+	// The best practice would be to do PHP first, but it seems this is not
+	// what the original ROM does; furthermore, pushing additional bytes to
+	// stack can wreck autostart softwaree loading at $0100
 	sei
 
 	// First, we wait for the talker to release the CLK line
@@ -107,8 +109,7 @@ iec_rx_clk_wait2:
 	// Timeout
 	jsr kernalstatus_EOI
 	pla
-	plp
-    
+	
 	// Restore registers
 	pla
 	tay
@@ -116,6 +117,7 @@ iec_rx_clk_wait2:
 	tax
     
 	sec // XXX confirm that sec is really a way to report timeout here
+	cli
 	rts
 !:
 	// More bits?
@@ -130,9 +132,6 @@ iec_rx_clk_wait2:
 
 	// Retreive the received byte
 	pla
-
-	// Return no-error
-	plp
 	
 	// Restore registers
 	sta TBTCNT // $A4 is a byte buffer according to http://sta.c64.org/cbm64mem.html
@@ -143,5 +142,6 @@ iec_rx_clk_wait2:
 	lda TBTCNT
 
 	clc
+	cli
 	rts
 

c64/kernal/iec/iec_tx_byte.s

@@ -26,7 +26,9 @@ iec_tx_byte:
 iec_tx_common:
 
 	// Timing is critical here - execute on disabled IRQs
-	php
+	// The best practice would be to do PHP first, but it seems this is not
+	// what the original ROM does; furthermore, pushing additional bytes to
+	// stack can wreck autostart softwaree loading at $0100
 	sei
 
 	// Wait till all receivers are ready, they should all release DATA
@@ -79,7 +81,7 @@ iec_tx_common_bit_is_sent:
 	dex
 	bpl iec_tx_common_sendbit
 
-	plp
+	cli
 
 	// Give device time to tell if they are busy by pulling DATA
 	// They should do it within 1ms