fixes for sending file name to IEC in LOAD

c64/kernal/iec_tx_byte.s

@@ -1,9 +1,12 @@
 
 ;; Implemented based on https://www.pagetable.com/?p=1135, https://github.com/mist64/cbmbus_doc
 
+;; Carry flag set = signal EOI
+
 iec_tx_byte:
 
 	pha
+	php
 
 	;; Notify all devices that we are going to send a byte
 	;; and it is going to be a data byte (released ATN)
@@ -12,6 +15,7 @@ iec_tx_byte:
 	;; Common part of iec_txbyte and iec_tx_common - waits for devices
 	;; and transmits a byte
 
+	plp
 	pla
 	jsr iec_tx_common
 	

c64/kernal/iec_tx_command.s

@@ -36,6 +36,7 @@ iec_tx_command:
 	;; Common part of iec_txbyte and iec_tx_common - waits for devices
 	;; and transmits a byte
 
+	clc ; Carry flag set is used for EOI mark
 	pla
 	jsr iec_tx_common
 

c64/kernal/iec_tx_common.s

@@ -5,19 +5,38 @@
 
 iec_tx_common:
 
-	;; Store the bye to send on a stack
+	;; Store the byte to send on a stack
 	pha
 	
+	;; Store the status register - carry flag is used to determine whether
+	;; this is the last byte of the stream
+	php
+	
 	;; Wait till all receivers are ready, they should all release DATA
 	jsr iec_wait_for_data_release
 
+	;; At this point a delay 256 usec or more is considered EOI - add waits if necessary
+	plp
+	bcc +
+	jsr iec_wait100us
+	jsr iec_wait100us
+	jsr iec_wait60us
+
+	;; XXX waits above should be enough - why do we need more waits???
+	jsr iec_wait100us
+	jsr iec_wait100us
+	jsr iec_wait100us
+
+	;; Receiver should now acknowledge EOI by pulling data for at least 60 usec
+	jsr iec_wait60us
+	jsr iec_wait_for_data_release
+*
 	;; Pull CLK back to indicate that DATA is not valid, keep it for 60us
 	;; We can use this routine as we don't hold DATA anyway (and its state doesn't even matter)
-	;; 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
@@ -39,7 +58,7 @@ iec_tx_common_bit_is_sent:
 
 	;; Wait 20us, so that device(s) can pick DATA
 	jsr iec_wait20us
-	
+		
 	;; Pull CLK for 20us again, before sending the next bit
 	;; or performing any other action
 	jsr iec_pull_clk_release_data

c64/kernal/iec_tx_eoi.s

@@ -1,15 +0,0 @@
-
-iec_tx_eoi:
-
-	;; Releasing ATN needed due to current iec_tx_command implementation
-	jsr iec_release_atn
-
-	;; Wait at least 256 usec
-	jsr iec_wait100us
-	jsr iec_wait100us
-	jsr iec_wait60us
-
-	;; Restore the bus to idle state
-	jsr iec_set_idle
-
-	rts

c64/kernal/iec_wait100us.s

@@ -8,9 +8,6 @@ iec_wait100us:
 	;; NTSC:
 	;; - CPU frequency 1.022727 MHZ, we need to waste at least 103 cycles
 
-	;; Waste cycles by reading some unimportant memory location
-	;; (in a loop) in order not to clutter VICE debug logs
-
 	;; Waste cycles in a loop
 
 	ldy #$12   ; 2 cycles

c64/kernal/load.s

@@ -76,21 +76,28 @@ send_filename:
 	
 	ldx #<current_filename_ptr
 	jsr peek_under_roms
+	iny
 
 	;; Save Y because iec_tx_byte will corrupt it
 	tax
 	tya
 	pha
-	txa
 
+	;; Set Carry flag on the last file name character, to mark EOI
+	cmp current_filename_length
+	clc
+	bne +
+	sec
+*
+	txa
 	jsr iec_tx_byte
 
 	pla
 	tay
-	iny
 	jmp send_filename
 
 sent_filename:
+
 	;; Command device to unlisten to indicate end of file name. (p16)
 	jsr unlsn
 	bcs load_error