added proper buffer handling to several IEC commands

c64/kernal/close.s

@@ -25,11 +25,7 @@ close:
 
 	;; IEC device
 
-	;; First check whether we have something to be sent in the buffer
+	jsr iec_tx_flush ; make sure no byte is awaiting
-	lda C3PO
-	beq +
-	sec ; send it with EOI
-	jsr iec_tx_byte ; send the command regardless of the status
 *
 	lda SAT, y ; get secondary address
 	ora $E0 ; CLOSE command

c64/kernal/iec/iec_tx_command_finalize.s

@@ -1,5 +1,5 @@
 
-;; Routine to finalize these IEC commands which do not end in turnaround
+;; Routine to finalize some IEC commands - which do not end in turnaround and are not followed by others
 ;; Implemented based on https://www.pagetable.com/?p=1135, https://github.com/mist64/cbmbus_doc
 
 

c64/kernal/iec/iec_tx_common.s

@@ -5,6 +5,7 @@
 
 ;; 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?
 
 iec_tx_common:
 

c64/kernal/iec/iec_tx_flush.s

@@ -0,0 +1,15 @@
+
+;; Flush the IEC output buffer (if not empty) - send byte with EOI
+;;
+;; Preserves .X, .Y and .A registers
+
+iec_tx_flush:
+
+	pha
+	lda C3PO
+	beq +
+	sec ; send it with EOI
+	jsr iec_tx_byte ; send the command regardless of the status
+*
+	pla
+	rts

c64/kernal/listen.s

@@ -5,6 +5,7 @@
 ;; - [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
+;; - http://www.zimmers.net/anonftp/pub/cbm/programming/serial-bus.pdf
 ;;
 ;; CPU registers that has to be preserved (see [RG64]): .X, .Y
 ;;
@@ -12,10 +13,17 @@
 
 listen:
 
-	;; First check whether device number is correct
+	;; According to serial-bus.pdf (page 15) this routine flushes the IEC out buffer
+	jsr iec_tx_flush
+
+	;; Check whether device number is correct
 	jsr iec_devnum_check
 	bcs kernalerror_DEVICE_NOT_FOUND
+
 	;; Encode and execute the command
 	ora #$20
-	sta BSOUR
+
-	jmp iec_tx_command
+	jmp common_talk_listen
+
+
+

c64/kernal/second.s

@@ -18,9 +18,6 @@ second:
 	bcs kernalerror_FILE_NOT_INPUT
 
 	ora #$60
-	sta BSOUR
+
-	jsr iec_tx_command
+	jmp common_unlsn_second
-	bcs + ; branch if error
+
-	jmp iec_tx_command_finalize
-*
-	rts

c64/kernal/talk.s

@@ -5,6 +5,7 @@
 ;; - [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
+;; - http://www.zimmers.net/anonftp/pub/cbm/programming/serial-bus.pdf
 ;;
 ;; CPU registers that has to be preserved (see [RG64]): .X, .Y
 ;;
@@ -12,10 +13,19 @@
 
 talk:
 
-	;; First check whether device number is correct
+	;; According to serial-bus.pdf (page 15) this routine flushes the IEC out buffer
+	jsr iec_tx_flush
+
+	;; Check whether device number is correct
 	jsr iec_devnum_check
 	bcs kernalerror_DEVICE_NOT_FOUND
+
 	;; Encode and execute the command
 	ora #$40
+
+common_talk_listen: ; common part of TALK and LISTEN
+
 	sta BSOUR
 	jmp iec_tx_command
+
+

c64/kernal/tksa.s

@@ -18,15 +18,8 @@ tksa:
 	bcs kernalerror_FILE_NOT_INPUT
 
 	ora #$F0
-	sta BSOUR
+
-	jsr iec_tx_command
+	jmp common_untlk_tksa
-	bcs + ; branch if error
+
-	;; XXX - is it really the right place to do a turnaround? I've got some doubts
-	;; (it forces us to send the TKSA command 'manually' sometimes), but
-	;; Luigi Di Fraia (https://luigidifraia.wordpress.com/2017/06/27/codebase64-on-the-kernal-behaviour/)
-	;; claims TKSA Kernal routine actually does the turnaround
-	jmp iec_turnaround_to_listen
-*
-	rts
 
 

c64/kernal/unlsn.s

@@ -5,6 +5,7 @@
 ;; - [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
+;; - http://www.zimmers.net/anonftp/pub/cbm/programming/serial-bus.pdf
 ;;
 ;; CPU registers that has to be preserved (see [RG64]): .X, .Y
 ;;
@@ -12,19 +13,19 @@
 
 unlsn:
 
-	;; This routine is documented in 'Compute's Mapping the Commodore 64', page 224
+	;; According to serial-bus.pdf (page 15) this routine flushes the IEC out buffer
-	
+	jsr iec_tx_flush
-	;; First check whether we have something to be sent in the buffer
+
-	lda C3PO
-	beq +
-	sec ; send it with EOI
-	jsr iec_tx_byte ; send the command regardless of the status
-*
 	;; Buffer empty, send the command
 	lda #$3F
+
+common_unlsn_second: ; common part of UNSLS and SECOND
+
 	sta BSOUR
 	jsr iec_tx_command
 	bcs + ; branch if error
 	jmp iec_tx_command_finalize
 *
 	rts
+
+

c64/kernal/untlk.s

@@ -5,6 +5,7 @@
 ;; - [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
+;; - http://www.zimmers.net/anonftp/pub/cbm/programming/serial-bus.pdf
 ;;
 ;; CPU registers that has to be preserved (see [RG64]): .X, .Y
 ;;
@@ -12,10 +13,21 @@
 
 untlk:
 
+	;; According to serial-bus.pdf (page 15) this routine flushes the IEC out buffer
+	jsr iec_tx_flush
+
+	;; Buffer empty, send the command
 	lda #$5F
+
+common_untlk_tksa: ; common part of UNTLK and TKSA
+
 	sta BSOUR
 	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
+	;; (it forces us to send the TKSA command 'manually' sometimes), but
+	;; Luigi Di Fraia (https://luigidifraia.wordpress.com/2017/06/27/codebase64-on-the-kernal-behaviour/)
+	;; claims TKSA Kernal routine actually does the turnaround
 	jmp iec_turnaround_to_listen
 *
 	rts