more work on IEC - finished tx part rework

.gitignore

@@ -1,14 +1,26 @@
+
+# Intermediate compilation files
+
 c64/basic/combined.s
 c64/kernal/combined.s
 temp.s
 temp.map
-newbasic
+
-newkern
-newrom
 src/compress_text
+src/pngprepare
 src/preprocess
 ophis.bin
 c64/basic/OUT.BIN
 c64/kernal/OUT.BIN
-*project
 
+# Compilation output
+
+chargen
+newbasic
+newkern
+newrom
+
+# Various IDE project files, temporary files, etc.
+
+*project
+.*swp

c64/kernal/iec_release_atn_clk_data.s

@@ -0,0 +1,7 @@
+
+iec_release_atn_clk_data:
+	lda CI2PRA
+	and #$FF - BIT_CI2PRA_ATN_OUT - BIT_CI2PRA_CLK_OUT - BIT_CI2PRA_DAT_OUT    ; release
+	sta CI2PRA
+	rts
+

c64/kernal/iec_tx_byte.s

@@ -5,6 +5,17 @@ iec_tx_byte:
 
 	pha
 
-;; XXX to be filled-in
+	;; Notify all devices that we are going to send a byte
+	;; and it is going to be a data byte (released ATN)
+	jsr iec_release_atn_clk_data
+
+	;; Common part of iec_txbyte and iec_tx_common - waits for devices
+	;; and transmits a byte
+
+	pla
+	jsr iec_tx_common
+
+	;; All done
+	clc
 	rts
 

c64/kernal/iec_tx_command.s

@@ -29,68 +29,17 @@ iec_tx_command:
 	;; 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
 	;; ready (or bored with DOS attack...)
-	;; - release back CLK, keep DATA released
+	;; Release back CLK, keep DATA released - to ask devices for status.
-	;; - afterwards wait till all devices also release DATA
 
 	jsr iec_release_clk_data
-	jsr iec_wait_for_data_release
 
-	;; Pull CLK back to indicate that DATA is not valid, keep it for 60us
+	;; Common part of iec_txbyte and iec_tx_common - waits for devices
-	;; Don't wait too long, as 200us or more is considered EOI
+	;; and transmits a byte
-
-	jsr iec_pull_clk_release_data
-	jsr iec_wait60us
-
-	;; Now, we can start transmission of 8 bits of data
-	ldx #7
-	pla
-
-iec_tx_command_nextbit:
-	;; Is next bit 0 or 1?
-	lsr
-	pha
-	bcs +
-
-	;; Bit is 0
-	jsr iec_release_clk_pull_data
-	jmp iec_tx_command_bitset
-*
-	;; Bit is 1
-	jsr iec_release_clk_data
 	
-iec_tx_command_bitset:
-
-	;; Wait 20us, so that device(s) can pick DATA
-	jsr iec_wait20us
-
-	;; Pull CLK for 20us again
-	jsr iec_pull_clk_release_data
-	jsr iec_wait20us
-
-	;; More bits to send?
 	pla
-	dex
+	jsr iec_tx_common
-	bpl iec_tx_command_nextbit
 
-	;; XXX the flow below is REALLY dangerous, as if there are multiple devices,
+	;; All done
-	;; one can signal that it's busy much earlier (more than 100ms) than the other.
-	;; Can we do something about it?
-
-	;; All done - give devices time to tell if they are busy by pulling DATA
-	;; They should do it within 1ms
-	ldx #$FF
-*	lda CI2PRA
-	;; BPL here is checking that bit 7 of $DD00 clears,
-	;; i.e, that the DATA line is pulled by drive
-	bpl +
-	dex
-	bne -
-	bpl iec_tx_command_done
-*
-	;; Wait 100us to give busy devices some time
-	jsr iec_wait100us
-	
-iec_tx_command_done:
 
 	clc
 	rts

c64/kernal/iec_tx_common.s

@@ -0,0 +1,74 @@
+
+;; This is a common part of iec_tx_byte and iec_tx_command
+;; Implemented based on https://www.pagetable.com/?p=1135, https://github.com/mist64/cbmbus_doc
+
+iec_tx_common:
+
+	;; Store the bye to send on a stack
+	pha
+
+	;; Wait till all receivers are ready, they should all release DATA
+	jsr iec_wait_for_data_release
+	
+	;; Pull CLK back to indicate that DATA is not valid, keep it for 60us
+	;; Don't wait too long, as 200us or more is considered EOI
+
+	jsr iec_pull_clk_release_data
+	jsr iec_wait60us
+
+	;; Now, we can start transmission of 8 bits of data
+	ldx #7
+	pla
+
+iec_tx_common_sendbit:
+	;; Is next bit 0 or 1?
+	lsr
+	pha
+	bcs +
+
+	;; Bit is 0
+	jsr iec_release_clk_pull_data
+	jmp iec_tx_common_bit_is_sent
+*
+	;; Bit is 1
+	jsr iec_release_clk_data
+	
+iec_tx_common_bit_is_sent:
+
+	;; Wait 20us, so that device(s) can pick DATA
+	jsr iec_wait20us
+
+	;; More bits to send?
+	pla
+	dex
+	bpl iec_tx_common_nextbit
+	
+	;; XXX the flow below is REALLY dangerous, as if there are multiple devices,
+	;; one can signal that it's busy much earlier (more than 100ms) than the other.
+	;; Can we do something about it?
+
+	;; All done - give devices time to tell if they are busy by pulling DATA
+	;; They should do it within 1ms
+	ldx #$FF
+*	lda CI2PRA
+	;; BPL here is checking that bit 7 of $DD00 clears,
+	;; i.e, that the DATA line is pulled by drive
+	bpl +
+	dex
+	bne -
+	bpl iec_tx_common_done
+*
+	;; Wait 100us to give busy devices some time
+	jsr iec_wait100us
+	
+iec_tx_common_done:
+	;; Byte sent, return
+	rts
+	
+iec_tx_common_nextbit:
+
+	;; Pull CLK for 20us again, before
+	jsr iec_pull_clk_release_data
+	jsr iec_wait20us
+	
+	jmp iec_tx_common_sendbit

c64/kernal/iec_tx_eoi.s

@@ -0,0 +1,11 @@
+
+iec_tx_eoi:
+
+	;; Wait at least 200us
+	jsr iec_wait100us
+	jsr iec_wait100us
+
+	;; Restore the bus to idle state
+	jsr iec_set_idle
+
+	rts