robustness improvements in IEC support

c64/kernal/iec_pull_atn_clk_release_data.s

@@ -1,7 +1,15 @@
 
 iec_pull_atn_clk_release_data:
+
+	;; Pulled CLK = DATA considered invalid; for extra robustness on non-emulated
+	;; hardware give some lines few more cycles to stabilize; see page 10 of
+	;; http://www.zimmers.net/anonftp/pub/cbm/programming/serial-bus.pdf
+
 	lda CI2PRA
-	ora #BIT_CI2PRA_ATN_OUT + BIT_CI2PRA_CLK_OUT    ; pull
+	ora #BIT_CI2PRA_ATN_OUT          ; pull
+	sta CI2PRA
+	ora #BIT_CI2PRA_CLK_OUT          ; pull
+	sta CI2PRA
 	and #$FF - BIT_CI2PRA_DAT_OUT    ; release
 	sta CI2PRA
 	rts

c64/kernal/iec_pull_clk_release_data.s

@@ -1,7 +1,13 @@
 
 iec_pull_clk_release_data:
+
+	;; Pulled CLK = DATA considered invalid; for extra robustness on non-emulated
+	;; hardware give some lines few more cycles to stabilize; see page 10 of
+	;; http://www.zimmers.net/anonftp/pub/cbm/programming/serial-bus.pdf
+
 	lda CI2PRA
 	ora #BIT_CI2PRA_CLK_OUT          ; pull
+	sta CI2PRA
 	and #$FF - BIT_CI2PRA_DAT_OUT    ; release
 	sta CI2PRA
 	rts

c64/kernal/iec_pull_data_release_atn_clock.s

@@ -1,7 +1,15 @@
 
-iec_pull_data_release_atn_clock:
+iec_pull_data_release_atn_clk:
+
+	;; Released CLK = DATA considered valid; for extra robustness on non-emulated
+	;; hardware give some lines few more cycles to stabilize; see page 10 of
+	;; http://www.zimmers.net/anonftp/pub/cbm/programming/serial-bus.pdf
+	
 	lda CI2PRA
 	ora #BIT_CI2PRA_DAT_OUT         ; pull
-	and #$FF - BIT_CI2PRA_ATN_OUT - BIT_CI2PRA_CLK_OUT   ; release
+	sta CI2PRA
+	and #$FF - BIT_CI2PRA_CLK_OUT   ; release
+	sta CI2PRA
+	and #$FF - BIT_CI2PRA_ATN_OUT   ; release
 	sta CI2PRA
 	rts

c64/kernal/iec_release_atn_clk_data.s

@@ -1,7 +1,16 @@
 
 iec_release_atn_clk_data:
+
+	;; Released CLK = DATA considered valid; for extra robustness on non-emulated
+	;; hardware give some lines few more cycles to stabilize; see page 10 of
+	;; http://www.zimmers.net/anonftp/pub/cbm/programming/serial-bus.pdf
+
 	lda CI2PRA
-	and #$FF - BIT_CI2PRA_ATN_OUT - BIT_CI2PRA_CLK_OUT - BIT_CI2PRA_DAT_OUT    ; release
+	and #$FF - BIT_CI2PRA_ATN_OUT    ; release
+	sta CI2PRA
+	and #$FF - BIT_CI2PRA_DAT_OUT    ; release
+	sta CI2PRA
+	and #$FF - BIT_CI2PRA_CLK_OUT    ; release
 	sta CI2PRA
 	rts
 

c64/kernal/iec_release_clk_data.s

@@ -1,6 +1,13 @@
 
 iec_release_clk_data:
+
+	;; Released CLK = DATA considered valid; for extra robustness on non-emulated
+	;; hardware give some lines few more cycles to stabilize; see page 10 of
+	;; http://www.zimmers.net/anonftp/pub/cbm/programming/serial-bus.pdf
+
 	lda CI2PRA
-	and #$FF - BIT_CI2PRA_CLK_OUT - BIT_CI2PRA_DAT_OUT    ; release
+	and #$FF - BIT_CI2PRA_DAT_OUT    ; release
+	sta CI2PRA
+	and #$FF - BIT_CI2PRA_CLK_OUT    ; release
 	sta CI2PRA
 	rts

c64/kernal/iec_release_clk_pull_data.s

@@ -1,7 +1,13 @@
 
 iec_release_clk_pull_data:
+
+	;; Released CLK = DATA considered valid; for extra robustness on non-emulated
+	;; hardware give some lines few more cycles to stabilize; see page 10 of
+	;; http://www.zimmers.net/anonftp/pub/cbm/programming/serial-bus.pdf
+
 	lda CI2PRA
-	and #$FF - BIT_CI2PRA_CLK_OUT    ; release
 	ora #BIT_CI2PRA_DAT_OUT          ; pull
 	sta CI2PRA
+	and #$FF - BIT_CI2PRA_CLK_OUT    ; release
+	sta CI2PRA
 	rts

c64/kernal/iec_turnaround_to_listen.s

@@ -5,7 +5,7 @@
 iec_turnaround_to_listen:
 
 	;; Pull DATA, release CLK and ATN (we are not sending commands)
-	jsr iec_pull_data_release_atn_clock
+	jsr iec_pull_data_release_atn_clk
 
 	;; Wait for clock line to be pulled by the drive
 	ldx #$FF ; XXX should we really use that high number?

c64/kernal/listen.s

@@ -2,6 +2,8 @@
 
 listen:
 
-	;; This trivial routine is documented in 'Compute's Mapping the Commodore 64', page 223
+	;; 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
 	jmp iec_tx_command

c64/kernal/second.s

@@ -1,6 +1,8 @@
 ; Function defined on pp272-273 of C64 Programmers Reference Guide
 second:
 
-	;; This trivial routine is documented in 'C64 Programmer's Reference Guide', page 296
+	;; This trivial routine is documented in 'C64 Programmer's Reference Guide', page 296 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 #$60
 	jmp iec_tx_command

c64/kernal/talk.s

@@ -2,7 +2,9 @@
 
 talk:
 
-	;; This trivial routine is documented in 'Compute's Mapping the Commodore 64', page 223
+	;; This 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 #$40
 	jmp iec_tx_command
 

c64/kernal/tksa.s

@@ -3,6 +3,7 @@ tksa:
 
 	;; This routine is documented in 'C64 Programmer's Reference Guide', page 302 and
 	;; https://www.pagetable.com/?p=1031, , https://github.com/mist64/cbmbus_doc
+	and #$1F ; make sure bits encoding the command are cleared out
 	ora #$F0
 	jmp iec_tx_command