CD Block Clock: 16.9344 MHz
MCU Clock divider: 2.1168 MHz (cd clock / 8)

State at Reset:
	Status buffer is filled with zero
	Mechanism is reset
	Emulation state set to ES_CLOSING

HSCK active low
IRQ active high
CDCK active high

Main Loop:
	wait for subcode data for next frame
		seems to be delivered via a "bank" IRQ
	if servo is not in PLAY state
		set DOUT and EMP to inactive
		set MUTE to active
	elif Q subcode CRC is not valid
		set MUTE to active
	elif Q subcode CONTROL field indicates a DATA track
		set DOUT and MUTE to active
		set EMP to inactive
	else
		set DOUT and MUTE to inactive
		set EMP based on emphasis bit in Q subcode CONTROL field
	run drive emulation state machine
	if we received a valid command last loop
		populate status buffer based on request format (see table below)
		if drive error status is valid
			override status format (2nd nibble) to RF_NOTREADY
			put error status in STATUS (1st nibble) of status buffer
			set error status valid to false
		else
			put drive status in STATUS (1st nibble) of status buffer
	Communication with Host via gate array:
		goes to fail state if HSCK is active (i.e. low)
		IRQ line is asserted
		Waits ~2ms (4234 cycles) for HSCK to go active (i.e lo)
			on timeout, resets outputs to host to inactive and quits comms this loop
		deasserts irq
		Sends 10 status nibbles
			nibbles are inverted
			HSCK is handshake from host
			CDCK is handshake frm MCU
			minimum 77 cycles per nibble

			HSCK 1 (inactive) -> 0 (active)
			nibble output
			CDCK 0 (inactive) ->1 (active)
			HSCK 0->1
			CDCK 1->0
		sets status sent flag
		Gets 10 command nibbles
			HSCK 1->0
			nibble input
			CDCK 0->1
			HSCK 0->1
			CDCK 1->0
		Entire status/command transfer has timeout of ~3ms (6351 cycles)
			on timeout, resets outputs to host to inactive and quits comms this loop
		sets command received flag
		Checksum of command is checked
			if bad, resets outputs to host to inactive and quits comms this loop
		set command valid flag
		resets outputs to host to inactive
	Runs command from host
		Generally comms failures cause it to just run a Nop command
		checksum failures cause drive error status to be set to STATUS_SUMERROR
		command is specified by first 2 nibbles of command packet
		second nibble must be zero or command is invalid
		first nibble must be < 0xE and != 0x5 or command is invalid
		command is sent to PC
		command implementation is run


format Absolute
	if Q subcode CRC is bad OR Q subcode Control ADR mode is not 1 or Q subcode tracknum indicates leadin
		set status format (2nd nibble) to RF_NOTREADY
	else
		store Absolute (RF_A == 0) in status format (2nd nibble)
		copy ATIME in BCD format from Q subcode buffer to 3rd through 8th nibble (inclusive)
		store flags in 9th nibble
			these seem to correspond to the data, emphasis and mute control bits sent to CD hardware
format Relative
	if Q subcode CRC is bad OR Q subcode Control ADR mode is not 1 or Q subcode tracknum indicates leadin
		set status format (2nd nibble) to RF_NOTREADY
	else
		store Relative (RF_R == 1) in status format (2nd nibble)
		copy relative track TIME in BCD format from Q subcode buffer to 3rd through 8th nibble (inclusive)
		store flags in 9th nibble
			these seem to correspond to the data, emphasis and mute control bits sent to CD hardware
format Track
	if Q subcode CRC is bad OR Q subcode Control ADR mode is not 1 or Q subcode tracknum indicates leadin
		set status format (2nd nibble) to RF_NOTREADY
	else
		store Track (RF_T == 2) in status format (2nd nibble)
		copy track number to 3rd and 4th status buffer nibbles
		copy Q subcode CONTROL field to 5th status buffer nibble
		copy Q subcode ADR field to 6th status buffer nibble
		store flags in 9th nibble
			these seem to correspond to the data, emphasis and mute control bits sent to CD hardware
format TOCO
	if disc is not validated
		set status format (2nd nibble) to RF_NOTREADY
	else
		set status format (2nd nibble) to RF_TOCO(3)
		copy leadout start in MM:SS:FF format (BCD) to 3rd through 8th nibble (inclusive)
	store flags in 9th nibble
		these seem to correspond to the data, emphasis and mute control bits sent to CD hardware
format TOCT
	if disc is not validated
		set status format (2nd nibble) to RF_NOTREADY
	else
		set status format (2nd nibble) to RF_TOCT(4)
		copy first track number in BCD format to 3rd and 4th nibbles
		copy last track number in BCD format to 5th and 6th nibbles
		copy TOCTVERSION(0) in BCD format to 7th and 8th nibbles
	store flags in 9th nibble
		these seem to correspond to the data, emphasis and mute control bits sent to CD hardware
format TOCN
	if disc is not validated
		set status format (2nd nibble) to RF_NOTREADY
		store flags in 9th nibble
			these seem to correspond to the data, emphasis and mute control bits sent to CD hardware
	else
		set status format (2nd nibble) to RF_TOCN(5)
		if requested trac is not valid
			set status format (2nd nibble) to RF_NOTREADY(F)
			store flags in 9th nibble
				these seem to correspond to the data, emphasis and mute control bits sent to CD hardware
		else
			copy track start time in MM:SS:FF format (BCD) to 3rd through 8th nibble (includisve)
			if track is a data track, force MSB of frame to 1
				notably, since frame numbers sould be <75 this bit would always be zero otherwise
			store low nibble of BCD track number in 8th nibble
format Error
	set status format (2nd nibble) to RF_E(6)
	error number is placed in 3rd nibble
		note emulator always writes 0
	store flags in 9th nibble
		these seem to correspond to the data, emphasis and mute control bits sent to CD hardware

state Stopping:
	if servo is in STOP status
		if disc is known present or disc status is unknown
			set drive status to STOP
		else
			set drive status to NODISC
state TOCing:
	if servo is in STOP status
		if focus is in NOTFOCUSING status
			set haveDisc to FALSE
			set haveDiscValid to TRUE
			set drive status to NODISC
		else
			do nothing this tick
	elif haveDisc is FALSE
		do nothing this tick (comments suggest this is an abnormal situation)
	else
		set drive status to TOCREAD
		if servo is NOT in PLAY status
			stop here
		if haveTOCValid is FALSE
			process current Q subcode data for TOC entry (see GetTOC)
			if TOC reading is done
				set haveTOCValid to true
				SEEK command is set to mechanism for PBA of program area start
				stop until next tick
			else
				stop until next tick
		else
			if havePAValid is TRUE (comments say this isn't supposed to happen)
				PAUSE command is sent to mechanism
			else
				check Q subcode data to see if we have found the start of the Program Area
				if we have
					set havePAValid to TRUE
					SEEK command for start of first track is sent to mechanism
					PAUSE command is sent to mechanism
				else if current block Q subcode is invalid or not Mode 1
					SEEK to next block
				else
					SEEK forward 250 blocks
state Reading:
state Seeking:
state Pausing:
state Playing:
state Cuing:
	These 5 states share a common implementation
	if servo status is STOP
		do nothing
	elif servo status is SEEK
		if mechanism error status is NOERROR
			set drive status to SEEK
		else
			STOP command sent to mechanism
			emulation state set to STOPPING
	else
		if servo status is PAUSE
			if drive status is NOT DISCEND
				set drive status to PAUSE
		else
			if Q subcode CRC is bad OR Q Control ADR is not mode 1 OR Q subcode tracknum is not lead out
				set drive status to PLAY
			else
				PAUSE command sent to mechanism
				set drive status to DISCEND

state FWDing:
	if servo status is STOP
		do nothing
	elif servo status is SEEK
		if mechanism error status is NOERROR
			set drive status to SCAN
		else
			STOP command is sent to mechanism
			emulation state is set to STOPPING
	elif servo status is PAUSE
		set drive status to DISCEND
	else:
		set drive status to SCAN
		if Q subcode CRC is valid AND Q Control ADR is mode 1
			if Q subcode tracknum indicates leadout
				PAUSE command is sent to mechanism
				set drive status to DISCEND
			else
				if scanClock is 0
					get ATIME from current Q subcode block
					turn it into an LBA, then PBA
					Add 100 to it
					SEEK command sent to mechanism
					reset scanClock to SCANPLAYTIME(10)
state RVSing:
	if servo status is STOP
		do nothing
	elif servo status is SEEK
		if mechanism error status is NOERROR
			set drive status to SCAN
		else
			STOP command is sent to mechanism
			emulation state is set to STOPPING
	elif servo status is PAUSE
		do nothing
	else
		set drive status to SCAN
		if Q subcode CRC is valid AND Q Control ADR is mode 1
			if Q subcode tracknum indcates we're in the leadin area
				SEEK command is sent to mechanism for beginning of first track
				PLAY command is sent to mechanism
				Set emulation state to PLAYING
			else
				if scanClock is 0
					get ATIME from current Q subcode block
					turn it into an LBA, then PBA
					subtract 140 from it
					SEEK command sent to mechanism
					reset scanClock to SCANPLAYTIME(10)
state Skipping:
	if servo status is STOP
		do nothing
	elif servo status is SEEK
		if mechanism error status is NOERROR
			set drive status to TRACKING
		else
			STOP command is sent to mechanism
			emulation state is set to STOPPING
	elif servo status is PAUSE
		set drive status to PAUSE
	else
		PAUSE command sent to mechanism
state DoorClosing:
	if door state is CLOSING
		set drive status to TRAYMOVING
	elif door state is CLOSED
		set drive status to STOP
		set request format to absolute
		set emulation state to CLOSED
state DoorClosed:
	do nothing
state DoorOpening:
	if door state is OPENING
		set drive status to TRAYMOVING
	elif door state is OPEN
		set drive status to DOOROPEN
		set emulation state to OPEN
state DoorOpen:
	if door status is NOT one of OPEN or OPENING
		set emulation state to CLOSING

command Nop
command Stop
	set request format to absolute
	if drive status is not DOOROPEN and status is notTRAYMOVING
		send stop command to mechanism
		set emulation state to ES_STOPPING
command Report Request
	4th nibble specifies request type
	RF_A(0)
		set absolute time format
	RF_R(1)
		set relative time format
	RF_T(2)
		request current track info
	RF_TOCO(3)
		request disc completion time
		will be ignored if disc has not been validated yet
			drive error status will be set to COMMANDERROR
			request format will be set back to absolute
	RF_TOCT(4)
		request start/end tracks on disc
		if disc is validated and drive is stopped
			will seek to start of disc and pause there
			emulation state set to TOCing
		if disc is validated and drive is not stopped
			only request format is changed
		else
			prepares memory state for TOC read
			will seek to start of disc and tell mechanism to play
			emulation state set to TOCing
	RF_TOCN(5)
		request start time of track N
		if drivestatus is DOOROPEN, TRAYMOVING or STOP
			command will be ignore dand drive error status will be set to COMMANDERROR
			request format will be set back to absolute
		requested track number is in the 5th and 6th nibbles in BCD format
		SEEK command sent to mechanism for start of disc
		PAUSE command sent to mechansim
		emulation state set to TOCing
	RF_E(6)
		request error info

command Read
	if drive status is DOOROPEN or TRAYMOVING
		set drive error status to COMMANDERROR and stop processing command
	check request format, if it's TOCT or TOCN, force it to absolute
	if disc is not validated
		set drive error status to COMMANDERROR and stop processing command
	location specified in MM:SS:FF format (BCD) in the 3rd through 8th nibbles (inclusive)
	location is converted to an LBA
	if location >= leadout start
		set drive error status to COMMANDERROR and stop processing command
	program area offset is added to location to convert it to a physical block address
	PBA is adjusted back 4
	SEEK command is sent to mechanism for adjusted PBA
	PLAY command is sent to mechanism
	Emulation state set to Reading
command Seek
	Same as Read, except sends Pause instead of Play for second command to mechanism
	Emulation state set to Seeking
command Pause
	if drive status is DOOROPEN or TRAYMOVING or SCAN
		set drive error status to COMMANDERROR and stop processing command
	check request format, if it's TOCT or TOCN, force it to absolute
	if disc is not validated
		set drive error status to COMMANDERROR and stop processing command
	if drive status is STOP
		calculates PBA of first track from TOC
		PBA is NOT adjusted back
		send SEEK command to mechanism for calculated PBA
	send PAUSE to mechanism
	set emulation state to Pausing
command Play
	if drive status is DOOROPEN or TRAYMOVING or DISCEND or DISCIN
		set drive error status to COMMANDERROR and stop processing command
	check request format, if it's TOCT or TOCN, force it to absolute
	if disc is not validated
		set drive error status to COMMANDERROR and stop processing command
	if drive status is TOCREAD or STOP
		calculates PBA of first track from TOC
		PBA is adjusted back by 4
		SEEK command is sent to mechanism for adjusted PBA
	send PLAY command to mechanism
	set emulation state to Playing
command Fwd
	if drive status is NOT one of PLAY, PAUSE or DISCIN
		set drive error status to COMMANDERROR and stop processing command
	check request format, if it's TOCT or TOCN, force it to absolute
	if disc is not validated
		set drive error status to COMMANDERROR and stop processing command
	Send PLAY command to mechanism
	Emulation state set to Fwding
	scanClock is set to SCANPLAYTIME(10)??
command Rvs
	if drive status is NOT one of PLAY, PAUSE or DISCEND
		set drive error status to COMMANDERROR and stop processing command
	check request format, if it's TOCT or TOCN, force it to absolute
	if disc is not validated
		set drive error status to COMMANDERROR and stop processing command
	Send PLAY command to mechanism
	Emulation state set to Rvsing
command TrackSkip
	if drive status is NOT one of PLAY, PAUSE or DISCEND
		set drive error status to COMMANDERROR and stop processing command
	check request format, if it's TOCT or TOCN, force it to absolute
	if disc is not validated
		set drive error status to COMMANDERROR and stop processing command
	direction to skip is in 4th nibble of command
	number of tracks to skip is a 16-bit value in the 5th-8th nibbles
		note tese are physical tracks i.e. loops of the spiral
	SKIP command is sent to mechanism
	PAUSE command is sent to mechanism
	emulation state is set to TSkping
command TrackCue
	if drive status is NOT one of STOP, PLAY, PAUSE, DISCEND, DISCIN or TOCREAD
		set drive error status to COMMANDERROR and stop processing command
	if drive status is TOCREAD
		check request format, if it's TOCT or TOCN, force it to absolute
		if disc is not validated
			set drive error status to COMMANDERROR and stop processing command
	track number is in nibbles 3 and 4 in BCD format
	calculates PBA of requested track from TOC
	Sends SEEK command to mechanism for calculated PBA
	if drive status at start of command was STOP, DISCEND or DISCIN
		send PLAY command to mechanism
	emulation state is set to CUING
command DoorClose
	if drive status is NOT one of DOOROPEN or TRAYMOVING
		set drive error status to COMMANDERROR and stop processing command
	CLOSE command is set to mechanism
	emulation state is set to CLOSING
command DoorOpen
	if drive status is DOOROPEN
		set drive error status to COMMANDERROR and stop processing command
	if drive servo is not stopped:
		set request format to absolute
	OPEN command is sent to mechanism
	emulation state set to OPENING
	disc, TOC and program area validitly flags are cleared