lds		YL, usbInputBuf		;2 reposition to buffer start	sub		cnt, YL				;1 length of message	ldi		x1, 1<<USB_INTR_PENDING_BIT	;1	cpi		cnt, 3				;1	out		USB_INTR_PENDING, x1;1 clear pending intr and check flag later. SE0 must be over. {,10} into next frame	brlo	rxDoReturn			;1 ensure valid packet size, ignore others	ld		x1, y				;2 PID	ldd		x2, y+1				;2 ADDR + 1 bit endpoint number	mov		x3, x2				;1 store for endpoint number	andi	x2, 0x7f			;1 mask endpoint number bit	lds		shift, usbDeviceId	;2	cpi		x1, USBPID_SETUP	;1	breq	isSetupOrOut		;2 -> 19 = {13, 21} from SE0 end	cpi		x1, USBPID_OUT		;1	breq	isSetupOrOut		;2 -> 22 = {16, 24} from SE0 end / {,24} into next frame	cpi		x1, USBPID_IN		;1	breq	handleIn			;1	cpi		x1, USBPID_DATA0	;1	breq	isData				;1	cpi		x1, USBPID_DATA1	;1	brne	rxDoReturn			;1 ignore all other PIDsisData:	lds		x2, usbCurrentTok	;2	tst		x2					;1	breq	rxDoReturn			;1 for other device or spontaneous data -- ignore	lds		x1, usbRxLen		;2	cpi		x1, 0				;1	brne	sendNakAndReti		;1 no buffer space available / {30, 38} from SE0 end	sts		usbRxLen, cnt		;2 store received data, swap buffers	sts		usbRxToken, x2		;2	lds		x1, usbAppBuf		;2	sts		usbAppBuf, YL		;2	sts		usbInputBuf, x1		;2 buffers now swapped	rjmp	sendAckAndReti		;2 -> {42, 50} from SE0 endhandleIn:						; {18, 26} from SE0 end	cp		x2, shift			;1 shift contains our device ID	brne	rxDoReturn			;1 other device#if USB_CFG_HAVE_INTRIN_ENDPOINT	sbrc	x3, 7				;2	rjmp	handleIn1			;0#endif	lds		cnt, usbTxLen		;2	cpi		cnt, -1				;1	breq	sendNakAndReti		;1 -> {27, 35} from SE0 end	ldi		x1, -1				;1	sts		usbTxLen, x1		;2 buffer is now free	ldi		YL, lo8(usbTxBuf)	;1	ldi		YH, hi8(usbTxBuf)	;1	rjmp	usbSendAndReti		;2 -> {34, 43} from SE0 end; Comment about when to set usbTxLen to -1:; We should set it back to -1 when we receive the ACK from the host. This would; be simple to implement: One static variable which stores whether the last; tx was for endpoint 0 or 1 and a compare in the receiver to distinguish the; ACK. However, we set it back to -1 immediately when we send the package,; assuming that no error occurs and the host sends an ACK. We save one byte; RAM this way and avoid potential problems with endless retries. The rest of; the driver assumes error-free transfers anyway.otherOutOrSetup:	clr		x1	sts		usbCurrentTok, x1rxDoReturn:	pop		x3					;2	pop		YL					;2	pop		YH					;2	rjmp	sofError			;2isSetupOrOut:					; we must be fast here -- a data package may follow / {,24} into next frame	cp		x2, shift			;1 shift contains our device ID	brne	otherOutOrSetup		;1 other device -- ignore	sts		usbCurrentTok, x1	;2#if 0	/* we implement only one rx endpoint */	sts		usbRxEndp, x3		;2 only stored if we may have to distinguish endpoints#endif;A transmission can still have data in the output buffer while we receive a;SETUP package with an IN phase. To avoid that the old data is sent as a reply,;we abort transmission. ### This mechanism assumes that NO OUT OR SETUP package;is ever sent to endpoint 1. We would abort transmission for endpoint 0;in this case.	ldi		x1, -1				;1	sts		usbMsgLen, x1		;2	sts		usbTxLen, x1		;2 abort transmission	pop		x3					;2	pop		YL					;2	in		x1, USB_INTR_PENDING;1	sbrc	x1, USB_INTR_PENDING_BIT;1 check whether data is already arriving {,41} into next frame	rjmp	shortcutToStart		;2 save the pops and pushes -- a new interrupt is aready pending;If the jump above was not taken, we can be at {,2} into the next frame here	pop		YH					;2sofError:						; error in start of frame -- ignore frame	ldi		x1, 1<<USB_INTR_PENDING_BIT;1 many int0 events occurred during our processing -- clear pending flag	out		USB_INTR_PENDING, x1;1	pop		shift				;2	pop		cnt					;2	pop		x2					;2	pop		x1					;2	out		SREG, x1			;1	pop		x1					;2	reti						;4 -> {,21} into next frame -> up to 3 sync bits missedsendNakAndReti:					; 21 cycles until SOP	ldi		YL, lo8(usbNakBuf)	;1	ldi		YH, hi8(usbNakBuf)	;1	rjmp	usbSendToken		;2sendAckAndReti:					; 19 cycles until SOP	ldi		YL, lo8(usbAckBuf)	;1	ldi		YH, hi8(usbAckBuf)	;1usbSendToken:	ldi		cnt, 2				;1;;;;rjmp	usbSendAndReti		fallthrough; USB spec says:; idle = J; J = (D+ = 0), (D- = 1) or USBOUT = 0x01; K = (D+ = 1), (D- = 0) or USBOUT = 0x02; Spec allows 7.5 bit times from EOP to SOP for replies (= 60 cycles);usbSend:;pointer to data in 'Y';number of bytes in 'cnt';uses: x1...x4, shift, cnt, YusbSendAndReti:				; SOP starts 16 cycles after call	push	x4				;2	in		x1, USBOUT		;1	cbr		x1,	USBMASK		;1 mask out data bits	ori		x1, USBIDLE		;1 idle	out		USBOUT, x1		;1 prepare idle state	ldi		x4, USBMASK		;1 exor mask	in		x2, USBDDR		;1	ori		x2, USBMASK		;1 set both pins to output	out		USBDDR, x2		;1 <-- acquire bus now; need not init x2 (bitstuff history) because sync starts with 0	ldi		shift, 0x80		;1 sync byte is first byte sent	rjmp	txLoop			;2 -> 13 + 3 = 16 cycles until SOP#if USB_CFG_HAVE_INTRIN_ENDPOINT	/* placed here due to relative jump range */handleIn1:	lds		cnt, usbTxLen1	cpi		cnt, -1	breq	sendNakAndReti	ldi		x1, -1	sts		usbTxLen1, x1	ldi		YL, lo8(usbTxBuf1)	ldi		YH, hi8(usbTxBuf1)	rjmp	usbSendAndReti#endifbitstuff0:					;1 (for branch taken)	eor		x1, x4			;1	ldi		x2, 0			;1	out		USBOUT, x1		;1 <-- out	rjmp	didStuff0		;2 branch back 2 cycles earlierbitstuff1:					;1 (for branch taken)	eor		x1, x4			;1	ldi		x2, 0			;1	sec						;1 set carry so that brsh will not jump	out		USBOUT, x1		;1 <-- out	rjmp	didStuff1		;2 jump back 1 cycle earlerbitstuff2:					;1 (for branch taken)	eor		x1, x4			;1	ldi		x2, 0			;1	rjmp	didStuff2		;2 jump back 3 cycles earlier and do outbitstuff3:					;1 (for branch taken)	eor		x1, x4			;1	ldi		x2, 0			;1	rjmp	didStuff3		;2 jump back earliertxLoop:	sbrs	shift, 0		;1	eor		x1, x4			;1	out		USBOUT, x1		;1 <-- out	ror		shift			;1	ror		x2				;1didStuff0:	cpi		x2, 0xfc		;1	brsh	bitstuff0		;1	sbrs	shift, 0		;1	eor		x1, x4			;1	ror		shift			;1	out		USBOUT, x1		;1 <-- out	ror		x2				;1	cpi		x2, 0xfc		;1didStuff1:	brsh	bitstuff1		;1	sbrs	shift, 0		;1	eor		x1, x4			;1	ror		shift			;1	ror		x2				;1didStuff2:	out		USBOUT, x1		;1 <-- out	cpi		x2, 0xfc		;1	brsh	bitstuff2		;1	sbrs	shift, 0		;1	eor		x1, x4			;1	ror		shift			;1	ror		x2				;1didStuff3:	cpi		x2, 0xfc		;1	out		USBOUT, x1		;1 <-- out	brsh	bitstuff3		;1	nop2					;2	ld		x3, y+			;2	sbrs	shift, 0		;1	eor		x1, x4			;1	out		USBOUT, x1		;1 <-- out	ror		shift			;1	ror		x2				;1didStuff4:	cpi		x2, 0xfc		;1	brsh	bitstuff4		;1	sbrs	shift, 0		;1	eor		x1, x4			;1	ror		shift			;1	out		USBOUT, x1		;1 <-- out	ror		x2				;1	cpi		x2, 0xfc		;1didStuff5:	brsh	bitstuff5		;1	sbrs	shift, 0		;1	eor		x1, x4			;1	ror		shift			;1	ror		x2				;1didStuff6:	out		USBOUT, x1		;1 <-- out	cpi		x2, 0xfc		;1	brsh	bitstuff6		;1	sbrs	shift, 0		;1	eor		x1, x4			;1	ror		shift			;1	ror		x2				;1didStuff7:	cpi		x2, 0xfc		;1	out		USBOUT, x1		;1 <-- out	brsh	bitstuff7		;1	mov		shift, x3		;1	dec		cnt				;1	brne	txLoop			;2 | 1	cbr		x1, USBMASK		;1 prepare SE0	pop		x4				;2	out		USBOUT, x1		;1 <-- out SE0	ldi		cnt, 4			;1 two bits = 16 cyclesse0Delay:	dec		cnt				;1	brne	se0Delay		;2 | 1	ori		x1, USBIDLE		;1	in		x2, USBDDR		;1	cbr		x2, USBMASK		;1 set both pins to input	out		USBOUT, x1		;1 <-- out J (idle)	cbr		x1, USBMASK		;1 configure no pullup on both pins	pop		x3				;2	pop		YL				;2	out		USBDDR, x2		;1 <-- release bus now	out		USBOUT, x1		;1 set pullup state	pop		YH				;2	rjmp	sofError		;2 [we want to jump to rxDoReturn, but this saves cycles]bitstuff4:					;1 (for branch taken)	eor		x1, x4			;1	ldi		x2, 0			;1	out		USBOUT, x1		;1 <-- out	rjmp	didStuff4		;2 jump back 2 cycles earlierbitstuff5:					;1 (for branch taken)	eor		x1, x4			;1	ldi		x2, 0			;1	sec						;1 set carry so that brsh is not taken	out		USBOUT, x1		;1 <-- out	rjmp	didStuff5		;2 jump back 1 cycle earlierbitstuff6:					;1 (for branch taken)	eor		x1, x4			;1	ldi		x2, 0			;1	rjmp	didStuff6		;2 jump back 3 cycles earlier and do out therebitstuff7:					;1 (for branch taken)	eor		x1, x4			;1	ldi		x2, 0			;1	rjmp	didStuff7		;2 jump back 4 cycles earlier; ######################## utility functions ########################; extern unsigned usbCrc16(unsigned char *data, unsigned char len);; data: r24/25; len: r22; temp variables:;   r18: data byte;   r19: bit counter;   r20/21: polynomial;   r23: scratch;   r24/25: crc-sum;   r26/27=X: ptr.global	usbCrc16usbCrc16:	mov		XL, r24	mov		XH, r25	ldi		r24, 0xff	ldi		r25, 0xff	ldi		r20, lo8(0xa001)	ldi		r21, hi8(0xa001)crcByteLoop:	subi	r22, 1	brcs	crcReady	ld		r18, x+	ldi		r19, 8crcBitLoop:	mov		r23, r18	eor		r23, r24	lsr		r25	ror		r24	lsr		r18	sbrs	r23, 0	rjmp	crcNoXor	eor		r24, r20	eor		r25, r21crcNoXor:	dec		r19	brne	crcBitLoop	rjmp	crcByteLoopcrcReady:	com		r24	com		r25	ret