;; #LAYOUT# STD *        #TAKE
;; #LAYOUT# *   KERNAL_0 #TAKE
;; #LAYOUT# *   *        #IGNORE

; Implemented based on https://www.pagetable.com/?p=1135, https://github.com/mist64/cbmbus_doc

; Expects byte to send in TBTCNT ($A4 is a byte buffer according to http://sta.c64.org/cbm64mem.html)
; Carry flag set = signal EOI
;
; Preserves .X and .Y registers


!ifdef CONFIG_IEC {


iec_tx_command:

	; Store .X and .Y on the stack - preserve them
	+phx_trash_a
	+phy_trash_a

	; Notify all devices that we are going to send a byte
	; and it is going to be a command (pulled ATN)
	jsr iec_pull_atn_clk_release_data

	; Give devices time to respond (response is mandatory!) by pulling DATA
	jsr iec_wait1ms
	lda CIA2_PRA ; pulled DATA = highest bit 0 = 'plus'
	+bmi iec_return_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
	; ready (or bored with DOS attack...)
	; Release back CLK, keep DATA released - to ask devices for status.
	; From here on IRQs are disabled, as in iec_tx_byte: a listener takes a
	; talker that waits too long after the release for EOI

	sei
	jsr iec_release_clk_data

	; Common part of iec_txbyte and iec_tx_common - waits for devices
	; and transmits a byte

!ifdef CONFIG_MB_M65 {
	; Ensure 1 Mhz mode and disabled badlines
	jsr m65_speed_iec
}
	clc ; Carry flag set is used for EOI mark
	jmp iec_tx_common
}