ACPTR now preserves registers, changed IEC temporary byte storage

STATUS.md

@@ -79,7 +79,7 @@ NOTE: Even the 'DONE' routines won't support features described as missing in on
 | $FF9C   | MEMBOT | DONE     |                                               |
 | $FF9F   | SCNKEY | DONE     | could be better integrated with ROM (aliases) |
 | $FFA2   | SETTMO | NOT DONE |                                               |
-| $FFA5   | ACPTR  | PARTIAL  | * work in progress                            |
+| $FFA5   | ACPTR  | DONE     |                                               |
 | $FFA8   | CIOUT  | DONE     |                                               |
 | $FFAB   | UNTLK  | DONE     |                                               |
 | $FFAE   | UNLSN  | DONE     |                                               |

c64/aliases/,aliases_ram_lowmem.s

@@ -31,6 +31,9 @@
 
 	.alias TIME       $A0 ; $A0-$A2, jiffy clock
 
+	.alias IEC_TMP1   $A3 ; temporary variable for tape and IEC
+	.alias IEC_TMP2   $A4 ; temporary variable for tape and IEC
+
 	;; 2-byte location below seems to be a good place for temporary storage,
 	;; it seems used for timing during tape reads only - see:
 	;; - 'C64 Programmer's Reference Guide', page 314

c64/kernal/acptr.s

@@ -8,10 +8,8 @@
 ;; CPU registers that has to be preserved (see [RG64]): .Y
 ;;
 
-;; XXX preserve register Y!
 
 acptr:
-	;; XXX temporary implementation
 	jsr kernalstatus_reset
 	jmp iec_rx_byte
 

c64/kernal/close.s

@@ -29,7 +29,7 @@ close:
 *
 	lda SAT, y ; get secondary address
 	ora $E0 ; CLOSE command
-	sta BSOUR
+	sta IEC_TMP2
 	jsr iec_tx_command
 	bcs close_remove_from_table
 	jsr iec_tx_command_finalize

c64/kernal/iec/iec_rx_byte.s

@@ -1,9 +1,17 @@
-	;; Receive a byte from the IEC bus.
-	;; Implemented based on https://www.pagetable.com/?p=1135, https://github.com/mist64/cbmbus_doc,
-	;; http://www.zimmers.net/anonftp/pub/cbm/programming/serial-bus.pdf (page 11)
+;; Receive a byte from the IEC bus.
+;; Implemented based on https://www.pagetable.com/?p=1135, https://github.com/mist64/cbmbus_doc,
+;; http://www.zimmers.net/anonftp/pub/cbm/programming/serial-bus.pdf (page 11)
+;;
+;; Preserves .X and .Y registers
 
 iec_rx_byte:
 
+	;; Store .X and .Y on the stack - preserve them
+	txa
+	pha
+	tya
+	pha
+
 	;; Timing is critical here - execute on disabled IRQs
 	php
 	sei
@@ -96,12 +104,19 @@ iec_rx_clk_wait2:
 	dey                     ; 2 cycles
     bne iec_rx_clk_wait2    ; 3 cycles if jumped
     
-    ;; Timeout
-    jsr kernalstatus_EOI
-    pla
-    plp
-    sec ; XXX confirm that sec is really a way to report timeout here
-    rts
+	;; Timeout
+	jsr kernalstatus_EOI
+	pla
+	plp
+    
+	;; Restore registers
+	pla
+	tay
+	pla
+	tax
+    
+	sec ; XXX confirm that sec is really a way to report timeout here
+	rts
 *
 	;; More bits?
 	dex
@@ -118,6 +133,15 @@ iec_rx_clk_wait2:
 
 	;; Return no-error
 	plp
+	
+	;; Restore registers
+	sta IEC_TMP2 ; $A4 is a byte buffer according to http://sta.c64.org/cbm64mem.html
+	pla
+	tay
+	pla
+	tax
+	lda IEC_TMP2
+
 	clc
 	rts
 

c64/kernal/iec/iec_tx_byte.s

@@ -1,7 +1,9 @@
 
 ;; Implemented based on https://www.pagetable.com/?p=1135, https://github.com/mist64/cbmbus_doc
 
-;; Expects byte to send in BSOUR; Carry flag set = signal EOI
+;; Expects byte to send in IEC_TMP2 ($A4 is a byte buffer according to http://sta.c64.org/cbm64mem.html)
+;; Carry flag set = signal EOI
+;;
 ;; Preserves .X and .Y registers
 
 

c64/kernal/iec/iec_tx_command.s

@@ -1,7 +1,9 @@
 
 ;; Implemented based on https://www.pagetable.com/?p=1135, https://github.com/mist64/cbmbus_doc
 
-;; Expects command to send in BSOUR; Carry flag set = signal EOI
+;; Expects byte to send in IEC_TMP2 ($A4 is a byte buffer according to http://sta.c64.org/cbm64mem.html)
+;; Carry flag set = signal EOI
+;;
 ;; Preserves .X and .Y registers
 
 

c64/kernal/iec/iec_tx_common.s

@@ -3,9 +3,8 @@
 ;; Implemented based on https://www.pagetable.com/?p=1135, https://github.com/mist64/cbmbus_doc
 ;; and http://www.zimmers.net/anonftp/pub/cbm/programming/serial-bus.pdf
 
-;; Expects byte to send in BSOUR; Carry flag set = signal EOI
-
-;; XXX is it OK to use BSOUR for data exchange? Maybe there is a better way?
+;; Expects byte to send in IEC_TMP2 ($A4 is a byte buffer according to http://sta.c64.org/cbm64mem.html)
+;; Carry flag set = signal EOI
 
 iec_tx_common:
 
@@ -42,11 +41,10 @@ iec_tx_common:
 
 iec_tx_common_sendbit:
 	;; Is next bit 0 or 1?
-	lda BSOUR
+	lda IEC_TMP2
 	lsr
-	sta BSOUR
+	sta IEC_TMP2
 	bcs +
-	;; XXX we are actually destroying BSOUR here... is it allowed?
 
 	;; Bit is 0
 	jsr iec_release_clk_pull_data

c64/kernal/load.s

@@ -64,7 +64,7 @@ load:
 
 	;; Open channel #0 (p16)
 	lda #$F0 ; $F0 for TKSA + 0 for channel number
-	sta BSOUR
+	sta IEC_TMP2
 	jsr iec_tx_command
 	bcs lvs_load_verify_error
 	jsr iec_tx_command_finalize
@@ -89,7 +89,7 @@ load_send_filename:
 	sec
 *
 	;; Transmit one character
-	sta BSOUR
+	sta IEC_TMP2
 	jsr iec_tx_byte
 
 	jmp load_send_filename
@@ -106,7 +106,7 @@ load_filename_sent:
 	bcs lvs_load_verify_error
 
 	lda #$60 ; open channel / data (p3) , required according to p13
-	sta BSOUR
+	sta IEC_TMP2
 	jsr iec_tx_command
 	bcs lvs_load_verify_error
 
@@ -161,7 +161,7 @@ load_loop:
 	jsr listen
 
 	lda #$E0
-	sta BSOUR
+	sta IEC_TMP2
 	jsr iec_tx_command
 	jsr iec_tx_command_finalize
 

c64/kernal/talk.s

@@ -25,7 +25,7 @@ talk:
 
 common_talk_listen: ; common part of TALK and LISTEN
 
-	sta BSOUR
+	sta IEC_TMP2
 	jmp iec_tx_command
 
 

c64/kernal/unlsn.s

@@ -21,7 +21,7 @@ unlsn:
 
 common_unlsn_second: ; common part of UNSLS and SECOND
 
-	sta BSOUR
+	sta IEC_TMP2
 	jsr iec_tx_command
 	bcs + ; branch if error
 	jmp iec_tx_command_finalize

c64/kernal/untlk.s

@@ -21,7 +21,7 @@ untlk:
 
 common_untlk_tksa: ; common part of UNTLK and TKSA
 
-	sta BSOUR
+	sta IEC_TMP2
 	jsr iec_tx_command
 	bcs + ; branch if error
 	;; XXX - for TKSA, is it really the right place to do a turnaround? I've got some doubts