several IEC routines now properly preserve X/Y registers

STATUS.md

@@ -73,18 +73,18 @@ NOTE: Even the 'DONE' routines won't support features described as missing in on
 | $FF8A   | RESTOR | PARTIAL  | CBINV, NMINV, and USRCMD missing        |
 | $FF8D   | VECTOR | DONE     |                                         |
 | $FF90   | SETMSG | DONE     |                                         |
-| $FF93   | SECOND | PARTIAL  | * work in progress                      |
+| $FF93   | SECOND | DONE     |                                         |
-| $FF96   | TKSA   | PARTIAL  | should probably also do a turnaround    |
+| $FF96   | TKSA   | PARTIAL  | should it do a turnaround?              |
 | $FF99   | MEMTOP | DONE     |                                         |
 | $FF9C   | MEMBOT | DONE     |                                         |
 | $FF9F   | SCNKEY | DONE     | could be better integrated with ROM     |
 | $FFA2   | SETTMO | NOT DONE |                                         |
 | $FFA5   | ACPTR  | NOT DONE | * work in progress                      |
-| $FFA8   | CIOUT  | PARITAL  | * work in progress                      |
+| $FFA8   | CIOUT  | DONE     |                                         |
 | $FFAB   | UNTLK  | PARITAL  | * work in progress                      |
-| $FFAE   | UNLSN  | PARITAL  | * work in progress                      |
+| $FFAE   | UNLSN  | DONE     |                                         |
-| $FFB1   | LISTEN | PARTIAL  | * work in progress                      |
+| $FFB1   | LISTEN | DONE     |                                         |
-| $FFB4   | TALK   | PARTIAL  | * work in progress                      |
+| $FFB4   | TALK   | PARTIAL  | should it do a turnaround?              |
 | $FFB7   | READST | DONE     |                                         |
 | $FFBA   | SETFLS | DONE     |                                         |
 | $FFBD   | SETNAM | DONE     |                                         |

c64/kernal/ciout.s

@@ -8,7 +8,6 @@
 ;; CPU registers that has to be preserved (see [RG64]): .X, .Y
 ;;
 
-;; XXX currently does not preserve registers, to be fixed!
 
 ciout:
 
@@ -31,9 +30,8 @@ ciout_store_in_buffer:
 	
 ciout_send_byte:
 
-	;; Send previous data
-	lda BSOUR
 	clc ; don't send with EOI
 	jsr iec_tx_byte
+	inc C3PO ; iec_tx_byte sets it to 0, but we still have something to send
 	jmp ciout_store_in_buffer
 

c64/kernal/iec_return.s

@@ -0,0 +1,38 @@
+
+;;
+;; Helper routines to return with error/success
+;;
+;; All of them restore X/Y registers from stack,
+;; they take care about Carry flag,
+;; error return reeset IEC line to default state,
+;; take care about .A and IOSTATUS
+;;
+
+iec_return_success:
+
+	;; BSOUR is certainly not valid anymore
+	lda #$00
+	sta C3PO
+	;; Restore registers
+	pla
+	tay
+	pla
+	tax
+	;; Report success
+	clc
+	rts
+
+iec_return_DEVICE_NOT_FOUND:
+
+	;; Set IEC line to normal idle state
+	jsr iec_set_idle
+	;; BSOUR is certainly not valid anymore
+	lda #$00
+	sta C3PO
+	;; Restore registers
+	pla
+	tay
+	pla
+	tax
+	;; Report error
+	jmp kernalerror_DEVICE_NOT_FOUND

c64/kernal/iec_tx_byte.s

@@ -1,11 +1,16 @@
 
 ;; Implemented based on https://www.pagetable.com/?p=1135, https://github.com/mist64/cbmbus_doc
 
-;; Carry flag set = signal EOI
+;; Expects byte to send in BSOUR; Carry flag set = signal EOI
+;; Preserves .X and .Y registers
+
 
 iec_tx_byte:
 
-	;; Store byte to send on the stack
+	;; Store .X and .Y on the stack - preserve them
+	txa
+	pha
+	tya
 	pha
 
 	;; Notify all devices that we are going to send a byte
@@ -15,10 +20,9 @@ iec_tx_byte:
 	;; Common part of iec_txbyte and iec_tx_common - waits for devices
 	;; and transmits a byte
 
-	pla
 	jsr iec_tx_common
 	
-	;; All done - give device time to tell if they are busy by pulling DATA
+	;; Give device time to tell if they are busy by pulling DATA
 	;; They should do it within 1ms
 	ldx #$FF
 *	lda CIA2_PRA
@@ -27,15 +31,8 @@ iec_tx_byte:
 	bpl +
 	dex
 	bne -
-	bpl iec_tx_byte_error
+	bpl iec_return_DEVICE_NOT_FOUND
 *
-	;; All done
+	jmp iec_return_success
-	clc
-	rts
-
-iec_tx_byte_error:
-
-	jsr iec_set_idle
-	jmp kernalerror_DEVICE_NOT_FOUND
 
 

c64/kernal/iec_tx_command.s

@@ -1,9 +1,16 @@
 
 ;; 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
+;; Preserves .X and .Y registers
+
+
 iec_tx_command:
 
-	;; Store command to send on the stack
+	;; Store .X and .Y on the stack - preserve them
+	txa
+	pha
+	tya
 	pha
 
 	;; Notify all devices that we are going to send a byte
@@ -19,10 +26,7 @@ iec_tx_command:
 	beq +
 
 	;; No devices present on the bus, so we can immediately return with device not found	
-	pla
+	jmp iec_return_DEVICE_NOT_FOUND
-
-	jsr iec_set_idle
-	jmp kernalerror_DEVICE_NOT_FOUND
 *
 	;; At least one device responded, but they are still allowed to stall
 	;; (can be busy processing something), we have to wait till they are all
@@ -35,7 +39,6 @@ iec_tx_command:
 	;; and transmits a byte
 
 	clc ; Carry flag set is used for EOI mark
-	pla
 	jsr iec_tx_common
 
 	;; According to https://www.pagetable.com/?p=1135 there is some complicated and dangerous
@@ -50,8 +53,7 @@ iec_tx_command:
 	;; to wait for the DATA being pulled, as confirmation is expected from
 	;; a single device only - but not sure if it's worth the trouble
 
-	jsr iec_set_idle
+	jmp iec_return_DEVICE_NOT_FOUND
-	jmp kernalerror_DEVICE_NOT_FOUND
 *
 	;; All done
 	
@@ -60,5 +62,5 @@ iec_tx_command:
 	;; jsr iec_wait20us
 	;; jsr iec_set_idle
 
-	clc
+	jmp iec_return_success
-	rts
+

c64/kernal/iec_tx_common.s

@@ -3,15 +3,15 @@
 ;; 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
+
+
 iec_tx_common:
 
 	;; Timing is critical here - execute on disabled IRQs
 	php
 	sei
 
-	;; Store the byte to send on a stack
-	pha
-
 	;; Wait till all receivers are ready, they should all release DATA
 	jsr iec_wait_for_data_release
 
@@ -38,13 +38,14 @@ iec_tx_common:
 	
 	;; Now, we can start transmission of 8 bits of data
 	ldx #7
-	pla
 
 iec_tx_common_sendbit:
 	;; Is next bit 0 or 1?
+	lda BSOUR
 	lsr
-	pha
+	sta BSOUR
 	bcs +
+	;; XXX we are actually destroying BSOUR here... is it allowed?
 
 	;; Bit is 0
 	jsr iec_release_clk_pull_data
@@ -65,13 +66,8 @@ iec_tx_common_bit_is_sent:
 
 	;; More bits to send?
 	dex
-	bpl iec_tx_common_nextbit
+	bpl iec_tx_common_sendbit
-	pla
 
 	plp
 	rts ; Flow continues differently for data/command
 
-iec_tx_common_nextbit:
-
-	pla
-	jmp iec_tx_common_sendbit

c64/kernal/listen.s

@@ -4,16 +4,15 @@
 ;;
 ;; - [RG64] C64 Programmer's Reference Guide   - page 285
 ;; - [CM64] Compute's Mapping the Commodore 64 - page 223
+;; - https://www.pagetable.com/?p=1031, https://github.com/mist64/cbmbus_doc
 ;;
 ;; CPU registers that has to be preserved (see [RG64]): .X, .Y
 ;;
 
-;; XXX currently does not preserve registers, to be fixed!
 
 listen:
 
-	;; This trivial routine is documented in 'Compute's Mapping the Commodore 64', page 223 and
-	;; https://www.pagetable.com/?p=1031, , https://github.com/mist64/cbmbus_doc
 	and #$1F ; make sure bits encoding the command are cleared out
 	ora #$20
+	sta BSOUR
 	jmp iec_tx_command

c64/kernal/load.s

@@ -67,22 +67,16 @@ load_send_filename:
 	jsr peek_under_roms
 	iny
 
-	;; Save Y because iec_tx_byte will corrupt it
-	tax
-	tya
-	pha
-
 	;; Set Carry flag on the last file name character, to mark EOI
-	cmp FNLEN
+	cpy FNLEN
 	clc
 	bne +
 	sec
 *
-	txa
+	;; Transmit one character
+	sta BSOUR
 	jsr iec_tx_byte
 
-	pla
-	tay
 	jmp load_send_filename
 
 load_filename_sent:
@@ -98,6 +92,7 @@ load_filename_sent:
 	bcs lvs_load_verify_error
 
 	lda #$60 ; open channel / data (p3) , required according to p13
+	sta BSOUR
 	jsr iec_tx_command
 	bcs lvs_load_verify_error
 
@@ -156,6 +151,7 @@ load_loop:
 	jsr listen
 
 	lda #$E0
+	sta BSOUR
 	jsr iec_tx_command
 
 	;; Tell drive to unlisten

c64/kernal/open.s

@@ -82,12 +82,6 @@ open_iec:
 	;; XXX note: this is only a temporary test implementation, real 'open' does not send anything to IEC,
 	;; see http://www.zimmers.net/anonftp/pub/cbm/programming/serial-bus.pdf
 
-	;; Disable IRQs, since timing matters!
-	sei
-
-	;; Begin sending under attention
-	;; XXX jsr iec_assert_atn
-
 	;; Request device to talk
 	lda current_device_number
 	jsr talk
@@ -107,8 +101,5 @@ open_iec:
 	clc
 
 open_iec_error:
-	;; Re-enable interrupts and return
+	;; Carry flag will be set by low-level routines
-	;; (iec_tx_byte will have set/cleared C flag and put result code
-	;; in A if it was an error).
-	cli
 	rts

c64/kernal/second.s

@@ -4,16 +4,15 @@
 ;;
 ;; - [RG64] C64 Programmer's Reference Guide   - page 296
 ;; - [CM64] Compute's Mapping the Commodore 64 - page 223/224
+;; - https://www.pagetable.com/?p=1031, , https://github.com/mist64/cbmbus_doc
 ;;
 ;; CPU registers that has to be preserved (see [RG64]): .X, .Y
 ;;
 
-;; XXX currently does not preserve registers, to be fixed!
 
 second:
 
-	;; see also https://www.pagetable.com/?p=1031, , https://github.com/mist64/cbmbus_doc
-
 	and #$1F ; make sure bits encoding the command are cleared out
 	ora #$60
+	sta BSOUR
 	jmp iec_tx_command

c64/kernal/talk.s

@@ -4,18 +4,17 @@
 ;;
 ;; - [RG64] C64 Programmer's Reference Guide   - page 301/302
 ;; - [CM64] Compute's Mapping the Commodore 64 - page 223
+;; - https://www.pagetable.com/?p=1031, https://github.com/mist64/cbmbus_doc
 ;;
 ;; CPU registers that has to be preserved (see [RG64]): .X, .Y
 ;;
 
-;; XXX currently does not preserve registers, to be fixed!
+
 ;; XXX shouldn't this do a turnaround?
 
 talk:
 
-	;; See also https://www.pagetable.com/?p=1031, https://github.com/mist64/cbmbus_doc
-
 	and #$1F ; make sure bits encoding the command are cleared out
 	ora #$40
+	sta BSOUR
 	jmp iec_tx_command
-

c64/kernal/tksa.s

@@ -4,18 +4,18 @@
 ;;
 ;; - [RG64] C64 Programmer's Reference Guide   - page 302
 ;; - [CM64] Compute's Mapping the Commodore 64 - page 224
+;; - https://www.pagetable.com/?p=1031, https://github.com/mist64/cbmbus_doc
 ;;
 ;; CPU registers that has to be preserved (see [RG64]): .X, .Y
 ;;
 
-;; XXX currently does not preserve registers, to be fixed!
+
 ;; XXX shouldn't this do a turnaround?
 
 tksa:
 
-	;; See also https://www.pagetable.com/?p=1031, , https://github.com/mist64/cbmbus_doc
-
 	and #$1F ; make sure bits encoding the command are cleared out
 	ora #$F0
+	sta BSOUR
 	jmp iec_tx_command
 

c64/kernal/unlsn.s

@@ -4,11 +4,11 @@
 ;;
 ;; - [RG64] C64 Programmer's Reference Guide   - page 303
 ;; - [CM64] Compute's Mapping the Commodore 64 - page 224
+;; - https://www.pagetable.com/?p=1031, , https://github.com/mist64/cbmbus_doc
 ;;
 ;; CPU registers that has to be preserved (see [RG64]): .X, .Y
 ;;
 
-;; XXX currently does not preserve registers, to be fixed!
 
 unlsn:
 
@@ -17,15 +17,12 @@ unlsn:
 	;; First check whether we have something to be sent in the buffer
 	lda C3PO
 	beq +
-	lda BSOUR
 	sec ; send it with EOI
 	jsr iec_tx_byte		; XXX what about the status of this operation?
-	;; Mark the buffer as invalid
-	lda #$00
-	sta C3PO
 *
-	;; Buffer empty send the command
+	;; Buffer empty, send the command
 	lda #$3F
+	sta BSOUR
 	jmp iec_tx_command
 
 

c64/kernal/untlk.s

@@ -4,16 +4,17 @@
 ;;
 ;; - [RG64] C64 Programmer's Reference Guide   - page 304
 ;; - [CM64] Compute's Mapping the Commodore 64 - page 224
+;; - https://www.pagetable.com/?p=1031, , https://github.com/mist64/cbmbus_doc
 ;;
 ;; CPU registers that has to be preserved (see [RG64]): .X, .Y
 ;;
 
-;; XXX currently does not preserve registers, to be fixed!
+
 ;; XXX shouldn't this do a turnaround?
 
 untlk:
 
-	;; This trivial routine is documented in 'Compute's Mapping the Commodore 64', page 224
 	lda #$5F
+	sta BSOUR
 	jmp iec_tx_command