--- /dev/null
+/* Name: usbdrvasm18.inc
+ * Project: V-USB, virtual USB port for Atmel's(r) AVR(r) microcontrollers
+ * Author: Lukas Schrittwieser (based on 20 MHz usbdrvasm20.inc by Jeroen Benschop)
+ * Creation Date: 2009-01-20
+ * Tabsize: 4
+ * Copyright: (c) 2008 by Lukas Schrittwieser and OBJECTIVE DEVELOPMENT Software GmbH
+ * License: GNU GPL v2 (see License.txt), GNU GPL v3 or proprietary (CommercialLicense.txt)
+ */
+
+/* Do not link this file! Link usbdrvasm.S instead, which includes the
+ * appropriate implementation!
+ */
+
+/*
+General Description:
+This file is the 18 MHz version of the asssembler part of the USB driver. It
+requires a 18 MHz crystal (not a ceramic resonator and not a calibrated RC
+oscillator).
+
+See usbdrv.h for a description of the entire driver.
+
+Since almost all of this code is timing critical, don't change unless you
+really know what you are doing! Many parts require not only a maximum number
+of CPU cycles, but even an exact number of cycles!
+
+Note: This version is smaller than usbdrvasm18-crc.inc because it saves the CRC
+table. It's therefore suitable for boot loaders on boards @ 18 MHz. However, it
+is not as small as it could be, because loops are unrolled in the same way as in
+usbdrvasm18-crc.inc. There is room for optimization.
+*/
+
+
+;max stack usage: [ret(2), YL, SREG, YH, [sofError], bitcnt(x5), shift, x1, x2, x3, x4, cnt, ZL, ZH] = 14 bytes
+;nominal frequency: 18 MHz -> 12 cycles per bit
+; Numbers in brackets are clocks counted from center of last sync bit
+; when instruction starts
+;register use in receive loop to receive the data bytes:
+; shift assembles the byte currently being received
+; x1 holds the D+ and D- line state
+; x2 holds the previous line state
+; cnt holds the number of bytes left in the receive buffer
+; x4 is used as temporary register
+; x3 is used for unstuffing: when unstuffing the last received bit is inverted in shift (to prevent further
+; unstuffing calls. In the same time the corresponding bit in x3 is cleared to mark the bit as beening iverted
+; zl lower crc value and crc table index
+; zh used for crc table accesses
+
+
+
+macro POP_STANDARD ; 18 cycles
+ pop cnt
+ pop x5
+ pop x3
+ pop x2
+ pop x1
+ pop shift
+ pop x4
+ endm
+macro POP_RETI ; 7 cycles
+ pop YH
+ pop YL
+ out SREG, YL
+ pop YL
+ endm
+
+;macro CRC_CLEANUP_AND_CHECK
+; ; the last byte has already been xored with the lower crc byte, we have to do the table lookup and xor
+; ; x3 is the higher crc byte, zl the lower one
+; ldi ZH, hi8(usbCrcTableHigh);[+1] get the new high byte from the table
+; lpm x2, Z ;[+2][+3][+4]
+; ldi ZH, hi8(usbCrcTableLow);[+5] get the new low xor byte from the table
+; lpm ZL, Z ;[+6][+7][+8]
+; eor ZL, x3 ;[+7] xor the old high byte with the value from the table, x2:ZL now holds the crc value
+; cpi ZL, 0x01 ;[+8] if the crc is ok we have a fixed remainder value of 0xb001 in x2:ZL (see usb spec)
+; brne ignorePacket ;[+9] detected a crc fault -> paket is ignored and retransmitted by the host
+; cpi x2, 0xb0 ;[+10]
+; brne ignorePacket ;[+11] detected a crc fault -> paket is ignored and retransmitted by the host
+; endm
+
+
+USB_INTR_VECTOR:
+;order of registers pushed: YL, SREG, YH, [sofError], x4, shift, x1, x2, x3, x5, cnt, ZL, ZH
+ push YL ;[-28] push only what is necessary to sync with edge ASAP
+ in YL, SREG ;[-26]
+ push YL ;[-25]
+ push YH ;[-23]
+;----------------------------------------------------------------------------
+; Synchronize with sync pattern:
+;----------------------------------------------------------------------------
+;sync byte (D-) pattern LSb to MSb: 01010100 [1 = idle = J, 0 = K]
+;sync up with J to K edge during sync pattern -- use fastest possible loops
+;The first part waits at most 1 bit long since we must be in sync pattern.
+;YL is guarenteed to be < 0x80 because I flag is clear. When we jump to
+;waitForJ, ensure that this prerequisite is met.
+waitForJ:
+ inc YL
+ sbis USBIN, USBMINUS
+ brne waitForJ ; just make sure we have ANY timeout
+waitForK:
+;The following code results in a sampling window of < 1/4 bit which meets the spec.
+ sbis USBIN, USBMINUS ;[-17]
+ rjmp foundK ;[-16]
+ sbis USBIN, USBMINUS
+ rjmp foundK
+ sbis USBIN, USBMINUS
+ rjmp foundK
+ sbis USBIN, USBMINUS
+ rjmp foundK
+ sbis USBIN, USBMINUS
+ rjmp foundK
+ sbis USBIN, USBMINUS
+ rjmp foundK
+ sbis USBIN, USBMINUS
+ rjmp foundK
+ sbis USBIN, USBMINUS
+ rjmp foundK
+ sbis USBIN, USBMINUS
+ rjmp foundK
+#if USB_COUNT_SOF
+ lds YL, usbSofCount
+ inc YL
+ sts usbSofCount, YL
+#endif /* USB_COUNT_SOF */
+#ifdef USB_SOF_HOOK
+ USB_SOF_HOOK
+#endif
+ rjmp sofError
+foundK: ;[-15]
+;{3, 5} after falling D- edge, average delay: 4 cycles
+;bit0 should be at 30 (2.5 bits) for center sampling. Currently at 4 so 26 cylces till bit 0 sample
+;use 1 bit time for setup purposes, then sample again. Numbers in brackets
+;are cycles from center of first sync (double K) bit after the instruction
+ push x4 ;[-14]
+; [---] ;[-13]
+ lds YL, usbInputBufOffset;[-12] used to toggle the two usb receive buffers
+; [---] ;[-11]
+ clr YH ;[-10]
+ subi YL, lo8(-(usbRxBuf));[-9] [rx loop init]
+ sbci YH, hi8(-(usbRxBuf));[-8] [rx loop init]
+ push shift ;[-7]
+; [---] ;[-6]
+ ldi shift, 0x80 ;[-5] the last bit is the end of byte marker for the pid receiver loop
+ clc ;[-4] the carry has to be clear for receipt of pid bit 0
+ sbis USBIN, USBMINUS ;[-3] we want two bits K (sample 3 cycles too early)
+ rjmp haveTwoBitsK ;[-2]
+ pop shift ;[-1] undo the push from before
+ pop x4 ;[1]
+ rjmp waitForK ;[3] this was not the end of sync, retry
+; The entire loop from waitForK until rjmp waitForK above must not exceed two
+; bit times (= 24 cycles).
+
+;----------------------------------------------------------------------------
+; push more registers and initialize values while we sample the first bits:
+;----------------------------------------------------------------------------
+haveTwoBitsK:
+ push x1 ;[0]
+ push x2 ;[2]
+ push x3 ;[4]
+ ldi x2, 1<<USBPLUS ;[6] [rx loop init] current line state is K state. D+=="1", D-=="0"
+ push x5 ;[7] used by tx loop for bitcnt
+ push cnt ;[9]
+ ldi cnt, USB_BUFSIZE ;[11]
+
+
+;--------------------------------------------------------------------------------------------------------------
+; receives the pid byte
+; there is no real unstuffing algorithm implemented here as a stuffing bit is impossible in the pid byte.
+; That's because the last four bits of the byte are the inverted of the first four bits. If we detect a
+; unstuffing condition something went wrong and abort
+; shift has to be initialized to 0x80
+;--------------------------------------------------------------------------------------------------------------
+
+bitloopPid:
+ in x1, USBIN ;[0] sample line state
+ andi x1, USBMASK ;[1] filter only D+ and D- bits
+ breq nse0 ;[2] both lines are low so handle se0
+ eor x2, x1 ;[3] generate inverted of actual bit
+ sbrc x2, USBMINUS ;[4] set the carry if we received a zero
+ sec ;[5]
+ ror shift ;[6]
+ nop ;[7] ZL is the low order crc value
+ ser x4 ;[8] the is no bit stuffing check here as the pid bit can't be stuffed. if so
+ ; some error occured. In this case the paket is discarded later on anyway.
+ mov x2, x1 ;[9] prepare for the next cycle
+ brcc bitloopPid ;[10] while 0s drop out of shift we get the next bit
+ eor x4, shift ;[11] invert all bits in shift and store result in x4
+
+;--------------------------------------------------------------------------------------------------------------
+; receives data bytes and calculates the crc
+; the last USBIN state has to be in x2
+; this is only the first half, due to branch distanc limitations the second half of the loop is near the end
+; of this asm file
+;--------------------------------------------------------------------------------------------------------------
+
+rxDataStart:
+ in x1, USBIN ;[0] sample line state (note: a se0 check is not useful due to bit dribbling)
+ ser x3 ;[1] prepare the unstuff marker register
+ eor x2, x1 ;[2] generates the inverted of the actual bit
+ bst x2, USBMINUS ;[3] copy the bit from x2
+ bld shift, 0 ;[4] and store it in shift
+ mov x2, shift ;[5] make a copy of shift for unstuffing check
+ andi x2, 0xF9 ;[6] mask the last six bits, if we got six zeros (which are six ones in fact)
+ breq unstuff0 ;[7] then Z is set now and we branch to the unstuffing handler
+didunstuff0:
+ subi cnt, 1 ;[8] cannot use dec because it doesn't affect the carry flag
+ brcs nOverflow ;[9] Too many bytes received. Ignore packet
+ st Y+, x4 ;[10] store the last received byte
+ ;[11] st needs two cycles
+
+; bit1
+ in x2, USBIN ;[0] sample line state
+ andi x1, USBMASK ;[1] check for se0 during bit 0
+ breq nse0 ;[2]
+ andi x2, USBMASK ;[3] check se0 during bit 1
+ breq nse0 ;[4]
+ eor x1, x2 ;[5]
+ bst x1, USBMINUS ;[6]
+ bld shift, 1 ;[7]
+ mov x1, shift ;[8]
+ andi x1, 0xF3 ;[9]
+ breq unstuff1 ;[10]
+didunstuff1:
+ nop ;[11]
+
+; bit2
+ in x1, USBIN ;[0] sample line state
+ andi x1, USBMASK ;[1] check for se0 (as there is nothing else to do here
+ breq nOverflow ;[2]
+ eor x2, x1 ;[3] generates the inverted of the actual bit
+ bst x2, USBMINUS ;[4]
+ bld shift, 2 ;[5] store the bit
+ mov x2, shift ;[6]
+ andi x2, 0xE7 ;[7] if we have six zeros here (which means six 1 in the stream)
+ breq unstuff2 ;[8] the next bit is a stuffing bit
+didunstuff2:
+ nop2 ;[9]
+ ;[10]
+ nop ;[11]
+
+; bit3
+ in x2, USBIN ;[0] sample line state
+ andi x2, USBMASK ;[1] check for se0
+ breq nOverflow ;[2]
+ eor x1, x2 ;[3]
+ bst x1, USBMINUS ;[4]
+ bld shift, 3 ;[5]
+ mov x1, shift ;[6]
+ andi x1, 0xCF ;[7]
+ breq unstuff3 ;[8]
+didunstuff3:
+ nop ;[9]
+ rjmp rxDataBit4 ;[10]
+ ;[11]
+
+; the avr branch instructions allow an offset of +63 insturction only, so we need this
+; 'local copy' of se0
+nse0:
+ rjmp se0 ;[4]
+ ;[5]
+; the same same as for se0 is needed for overflow and StuffErr
+nOverflow:
+stuffErr:
+ rjmp overflow
+
+
+unstuff0: ;[8] this is the branch delay of breq unstuffX
+ andi x1, USBMASK ;[9] do an se0 check here (if the last crc byte ends with 5 one's we might end up here
+ breq didunstuff0 ;[10] event tough the message is complete -> jump back and store the byte
+ ori shift, 0x01 ;[11] invert the last received bit to prevent furhter unstuffing
+ in x2, USBIN ;[0] we have some free cycles so we could check for bit stuffing errors
+ andi x3, 0xFE ;[1] mark this bit as inverted (will be corrected before storing shift)
+ eor x1, x2 ;[2] x1 and x2 have to be different because the stuff bit is always a zero
+ andi x1, USBMASK ;[3] mask the interesting bits
+ breq stuffErr ;[4] if the stuff bit is a 1-bit something went wrong
+ mov x1, x2 ;[5] the next bit expects the last state to be in x1
+ rjmp didunstuff0 ;[6]
+ ;[7] jump delay of rjmp didunstuffX
+
+unstuff1: ;[11] this is the jump delay of breq unstuffX
+ in x1, USBIN ;[0] we have some free cycles so we could check for bit stuffing errors
+ ori shift, 0x02 ;[1] invert the last received bit to prevent furhter unstuffing
+ andi x3, 0xFD ;[2] mark this bit as inverted (will be corrected before storing shift)
+ eor x2, x1 ;[3] x1 and x2 have to be different because the stuff bit is always a zero
+ andi x2, USBMASK ;[4] mask the interesting bits
+ breq stuffErr ;[5] if the stuff bit is a 1-bit something went wrong
+ mov x2, x1 ;[6] the next bit expects the last state to be in x2
+ nop2 ;[7]
+ ;[8]
+ rjmp didunstuff1 ;[9]
+ ;[10] jump delay of rjmp didunstuffX
+
+unstuff2: ;[9] this is the jump delay of breq unstuffX
+ ori shift, 0x04 ;[10] invert the last received bit to prevent furhter unstuffing
+ andi x3, 0xFB ;[11] mark this bit as inverted (will be corrected before storing shift)
+ in x2, USBIN ;[0] we have some free cycles so we could check for bit stuffing errors
+ eor x1, x2 ;[1] x1 and x2 have to be different because the stuff bit is always a zero
+ andi x1, USBMASK ;[2] mask the interesting bits
+ breq stuffErr ;[3] if the stuff bit is a 1-bit something went wrong
+ mov x1, x2 ;[4] the next bit expects the last state to be in x1
+ nop2 ;[5]
+ ;[6]
+ rjmp didunstuff2 ;[7]
+ ;[8] jump delay of rjmp didunstuffX
+
+unstuff3: ;[9] this is the jump delay of breq unstuffX
+ ori shift, 0x08 ;[10] invert the last received bit to prevent furhter unstuffing
+ andi x3, 0xF7 ;[11] mark this bit as inverted (will be corrected before storing shift)
+ in x1, USBIN ;[0] we have some free cycles so we could check for bit stuffing errors
+ eor x2, x1 ;[1] x1 and x2 have to be different because the stuff bit is always a zero
+ andi x2, USBMASK ;[2] mask the interesting bits
+ breq stuffErr ;[3] if the stuff bit is a 1-bit something went wrong
+ mov x2, x1 ;[4] the next bit expects the last state to be in x2
+ nop2 ;[5]
+ ;[6]
+ rjmp didunstuff3 ;[7]
+ ;[8] jump delay of rjmp didunstuffX
+
+
+
+; the include has to be here due to branch distance restirctions
+#include "asmcommon.inc"
+
+
+
+; USB spec says:
+; idle = J
+; J = (D+ = 0), (D- = 1)
+; K = (D+ = 1), (D- = 0)
+; Spec allows 7.5 bit times from EOP to SOP for replies
+; 7.5 bit times is 90 cycles. ...there is plenty of time
+
+
+sendNakAndReti:
+ ldi x3, USBPID_NAK ;[-18]
+ rjmp sendX3AndReti ;[-17]
+sendAckAndReti:
+ ldi cnt, USBPID_ACK ;[-17]
+sendCntAndReti:
+ mov x3, cnt ;[-16]
+sendX3AndReti:
+ ldi YL, 20 ;[-15] x3==r20 address is 20
+ ldi YH, 0 ;[-14]
+ ldi cnt, 2 ;[-13]
+; rjmp usbSendAndReti fallthrough
+
+;usbSend:
+;pointer to data in 'Y'
+;number of bytes in 'cnt' -- including sync byte [range 2 ... 12]
+;uses: x1...x4, btcnt, shift, cnt, Y
+;Numbers in brackets are time since first bit of sync pattern is sent
+
+usbSendAndReti: ; 12 cycles until SOP
+ in x2, USBDDR ;[-12]
+ ori x2, USBMASK ;[-11]
+ sbi USBOUT, USBMINUS;[-10] prepare idle state; D+ and D- must have been 0 (no pullups)
+ in x1, USBOUT ;[-8] port mirror for tx loop
+ out USBDDR, x2 ;[-6] <- acquire bus
+ ldi x2, 0 ;[-6] init x2 (bitstuff history) because sync starts with 0
+ ldi x4, USBMASK ;[-5] exor mask
+ ldi shift, 0x80 ;[-4] sync byte is first byte sent
+txByteLoop:
+ ldi bitcnt, 0x40 ;[-3]=[9] binary 01000000
+txBitLoop: ; the loop sends the first 7 bits of the byte
+ sbrs shift, 0 ;[-2]=[10] if we have to send a 1 don't change the line state
+ eor x1, x4 ;[-1]=[11]
+ out USBOUT, x1 ;[0]
+ ror shift ;[1]
+ ror x2 ;[2] transfers the last sent bit to the stuffing history
+didStuffN:
+ nop ;[3]
+ nop ;[4]
+ cpi x2, 0xfc ;[5] if we sent six consecutive ones
+ brcc bitstuffN ;[6]
+ lsr bitcnt ;[7]
+ brne txBitLoop ;[8] restart the loop while the 1 is still in the bitcount
+
+; transmit bit 7
+ sbrs shift, 0 ;[9]
+ eor x1, x4 ;[10]
+didStuff7:
+ ror shift ;[11]
+ out USBOUT, x1 ;[0] transfer bit 7 to the pins
+ ror x2 ;[1] move the bit into the stuffing history
+ cpi x2, 0xfc ;[2]
+ brcc bitstuff7 ;[3]
+ ld shift, y+ ;[4] get next byte to transmit
+ dec cnt ;[5] decrement byte counter
+ brne txByteLoop ;[7] if we have more bytes start next one
+ ;[8] branch delay
+
+;make SE0:
+ cbr x1, USBMASK ;[8] prepare SE0 [spec says EOP may be 25 to 30 cycles]
+ lds x2, usbNewDeviceAddr;[9]
+ lsl x2 ;[11] we compare with left shifted address
+ out USBOUT, x1 ;[0] <-- out SE0 -- from now 2 bits = 24 cycles until bus idle
+ subi YL, 20 + 2 ;[1] Only assign address on data packets, not ACK/NAK in x3
+ sbci YH, 0 ;[2]
+;2006-03-06: moved transfer of new address to usbDeviceAddr from C-Code to asm:
+;set address only after data packet was sent, not after handshake
+ breq skipAddrAssign ;[3]
+ sts usbDeviceAddr, x2 ; if not skipped: SE0 is one cycle longer
+skipAddrAssign:
+;end of usbDeviceAddress transfer
+ ldi x2, 1<<USB_INTR_PENDING_BIT;[5] int0 occurred during TX -- clear pending flag
+ USB_STORE_PENDING(x2) ;[6]
+ ori x1, USBIDLE ;[7]
+ in x2, USBDDR ;[8]
+ cbr x2, USBMASK ;[9] set both pins to input
+ mov x3, x1 ;[10]
+ cbr x3, USBMASK ;[11] configure no pullup on both pins
+ ldi x4, 4 ;[12]
+se0Delay:
+ dec x4 ;[13] [16] [19] [22]
+ brne se0Delay ;[14] [17] [20] [23]
+ out USBOUT, x1 ;[24] <-- out J (idle) -- end of SE0 (EOP signal)
+ out USBDDR, x2 ;[25] <-- release bus now
+ out USBOUT, x3 ;[26] <-- ensure no pull-up resistors are active
+ rjmp doReturn
+
+bitstuffN:
+ eor x1, x4 ;[8] generate a zero
+ ldi x2, 0 ;[9] reset the bit stuffing history
+ nop2 ;[10]
+ out USBOUT, x1 ;[0] <-- send the stuffing bit
+ rjmp didStuffN ;[1]
+
+bitstuff7:
+ eor x1, x4 ;[5]
+ ldi x2, 0 ;[6] reset bit stuffing history
+ clc ;[7] fill a zero into the shift register
+ rol shift ;[8] compensate for ror shift at branch destination
+ rjmp didStuff7 ;[9]
+ ;[10] jump delay
+
+;--------------------------------------------------------------------------------------------------------------
+; receives data bytes and calculates the crc
+; second half of the data byte receiver loop
+; most parts of the crc algorithm are here
+;--------------------------------------------------------------------------------------------------------------
+
+nOverflow2:
+ rjmp overflow
+
+rxDataBit4:
+ in x1, USBIN ;[0] sample line state
+ andi x1, USBMASK ;[1] check for se0
+ breq nOverflow2 ;[2]
+ eor x2, x1 ;[3]
+ bst x2, USBMINUS ;[4]
+ bld shift, 4 ;[5]
+ mov x2, shift ;[6]
+ andi x2, 0x9F ;[7]
+ breq unstuff4 ;[8]
+didunstuff4:
+ nop2 ;[9][10]
+ nop ;[11]
+
+; bit5
+ in x2, USBIN ;[0] sample line state
+ nop ;[1] use the table for the higher byte
+ eor x1, x2 ;[2]
+ bst x1, USBMINUS ;[3]
+ bld shift, 5 ;[4]
+ mov x1, shift ;[5]
+ andi x1, 0x3F ;[6]
+ breq unstuff5 ;[7]
+didunstuff5:
+ nop2 ;[8] load the higher crc xor-byte and store it for later use
+ ;[9] lpm needs 3 cycles
+ nop ;[10]
+ nop ;[11] load the lower crc xor byte adress
+
+; bit6
+ in x1, USBIN ;[0] sample line state
+ eor x2, x1 ;[1]
+ bst x2, USBMINUS ;[2]
+ bld shift, 6 ;[3]
+ mov x2, shift ;[4]
+ andi x2, 0x7E ;[5]
+ breq unstuff6 ;[6]
+didunstuff6:
+ nop2 ;[7] load the lower xor crc byte
+ ;[8] lpm needs 3 cycles
+ nop ;[9]
+ nop ;[10] xor the old high crc byte with the low xor-byte
+ nop ;[11] move the new high order crc value from temp to its destination
+
+; bit7
+ in x2, USBIN ;[0] sample line state
+ eor x1, x2 ;[1]
+ bst x1, USBMINUS ;[2]
+ bld shift, 7 ;[3] now shift holds the complete but inverted data byte
+ mov x1, shift ;[4]
+ andi x1, 0xFC ;[5]
+ breq unstuff7 ;[6]
+didunstuff7:
+ eor x3, shift ;[7] x3 marks all bits which have not been inverted by the unstuffing subs
+ mov x4, x3 ;[8] keep a copy of the data byte it will be stored during next bit0
+ nop ;[9] feed the actual byte into the crc algorithm
+ rjmp rxDataStart ;[10] next byte
+ ;[11] during the reception of the next byte this one will be fed int the crc algorithm
+
+unstuff4: ;[9] this is the jump delay of rjmp unstuffX
+ ori shift, 0x10 ;[10] invert the last received bit to prevent furhter unstuffing
+ andi x3, 0xEF ;[11] mark this bit as inverted (will be corrected before storing shift)
+ in x2, USBIN ;[0] we have some free cycles so we could check for bit stuffing errors
+ eor x1, x2 ;[1] x1 and x2 have to be different because the stuff bit is always a zero
+ andi x1, USBMASK ;[2] mask the interesting bits
+ breq stuffErr2 ;[3] if the stuff bit is a 1-bit something went wrong
+ mov x1, x2 ;[4] the next bit expects the last state to be in x1
+ nop2 ;[5]
+ ;[6]
+ rjmp didunstuff4 ;[7]
+ ;[8] jump delay of rjmp didunstuffX
+
+unstuff5: ;[8] this is the jump delay of rjmp unstuffX
+ nop ;[9]
+ ori shift, 0x20 ;[10] invert the last received bit to prevent furhter unstuffing
+ andi x3, 0xDF ;[11] mark this bit as inverted (will be corrected before storing shift)
+ in x1, USBIN ;[0] we have some free cycles so we could check for bit stuffing errors
+ eor x2, x1 ;[1] x1 and x2 have to be different because the stuff bit is always a zero
+ andi x2, USBMASK ;[2] mask the interesting bits
+ breq stuffErr2 ;[3] if the stuff bit is a 1-bit something went wrong
+ mov x2, x1 ;[4] the next bit expects the last state to be in x2
+ nop ;[5]
+ rjmp didunstuff5 ;[6]
+ ;[7] jump delay of rjmp didunstuffX
+
+unstuff6: ;[7] this is the jump delay of rjmp unstuffX
+ nop2 ;[8]
+ ;[9]
+ ori shift, 0x40 ;[10] invert the last received bit to prevent furhter unstuffing
+ andi x3, 0xBF ;[11] mark this bit as inverted (will be corrected before storing shift)
+ in x2, USBIN ;[0] we have some free cycles so we could check for bit stuffing errors
+ eor x1, x2 ;[1] x1 and x2 have to be different because the stuff bit is always a zero
+ andi x1, USBMASK ;[2] mask the interesting bits
+ breq stuffErr2 ;[3] if the stuff bit is a 1-bit something went wrong
+ mov x1, x2 ;[4] the next bit expects the last state to be in x1
+ rjmp didunstuff6 ;[5]
+ ;[6] jump delay of rjmp didunstuffX
+
+unstuff7: ;[7] this is the jump delay of rjmp unstuffX
+ nop ;[8]
+ nop ;[9]
+ ori shift, 0x80 ;[10] invert the last received bit to prevent furhter unstuffing
+ andi x3, 0x7F ;[11] mark this bit as inverted (will be corrected before storing shift)
+ in x1, USBIN ;[0] we have some free cycles so we could check for bit stuffing errors
+ eor x2, x1 ;[1] x1 and x2 have to be different because the stuff bit is always a zero
+ andi x2, USBMASK ;[2] mask the interesting bits
+ breq stuffErr2 ;[3] if the stuff bit is a 1-bit something went wrong
+ mov x2, x1 ;[4] the next bit expects the last state to be in x2
+ rjmp didunstuff7 ;[5]
+ ;[6] jump delay of rjmp didunstuff7
+
+; local copy of the stuffErr desitnation for the second half of the receiver loop
+stuffErr2:
+ rjmp stuffErr
projects / pub / USBasp.git / blobdiff