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Diffstat (limited to 'usbdrv/usbdrvasm18-crc.inc')
| -rw-r--r-- | usbdrv/usbdrvasm18-crc.inc | 706 |
1 files changed, 706 insertions, 0 deletions
diff --git a/usbdrv/usbdrvasm18-crc.inc b/usbdrv/usbdrvasm18-crc.inc new file mode 100644 index 0000000..0ff2f42 --- /dev/null +++ b/usbdrv/usbdrvasm18-crc.inc @@ -0,0 +1,706 @@ +/* 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! +*/ + + +;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 +; x3 holds the higher crc byte (see algorithm below) +; x4 is used as temporary register for the crc algorithm +; x5 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 x5 is cleared to mark the bit as beening iverted +; zl lower crc value and crc table index +; zh used for crc table accesses + +;-------------------------------------------------------------------------------------------------------------- +; CRC mods: +; table driven crc checker, Z points to table in prog space +; ZL is the lower crc byte, x3 is the higher crc byte +; x4 is used as temp register to store different results +; the initialization of the crc register is not 0xFFFF but 0xFE54. This is because during the receipt of the +; first data byte an virtual zero data byte is added to the crc register, this results in the correct initial +; value of 0xFFFF at beginning of the second data byte before the first data byte is added to the crc. +; The magic number 0xFE54 results form the crc table: At tabH[0x54] = 0xFF = crcH (required) and +; tabL[0x54] = 0x01 -> crcL = 0x01 xor 0xFE = 0xFF +; bitcnt is renamed to x5 and is used for unstuffing purposes, the unstuffing works like in the 12MHz version +;-------------------------------------------------------------------------------------------------------------- +; CRC algorithm: +; The crc register is formed by x3 (higher byte) and ZL (lower byte). The algorithm uses a 'reversed' form +; i.e. that it takes the least significant bit first and shifts to the right. So in fact the highest order +; bit seen from the polynomial devision point of view is the lsb of ZL. (If this sounds strange to you i +; propose a research on CRC :-) ) +; Each data byte received is xored to ZL, the lower crc byte. This byte now builds the crc +; table index. Next the new high byte is loaded from the table and stored in x4 until we have space in x3 +; (its destination). +; Afterwards the lower table is loaded from the table and stored in ZL (the old index is overwritten as +; we don't need it anymore. In fact this is a right shift by 8 bits.) Now the old crc high value is xored +; to ZL, this is the second shift of the old crc value. Now x4 (the temp reg) is moved to x3 and the crc +; calculation is done. +; Prior to the first byte the two CRC register have to be initialized to 0xFFFF (as defined in usb spec) +; however the crc engine also runs during the receipt of the first byte, therefore x3 and zl are initialized +; to a magic number which results in a crc value of 0xFFFF after the first complete byte. +; +; This algorithm is split into the extra cycles of the different bits: +; bit7: XOR the received byte to ZL +; bit5: load the new high byte to x4 +; bit6: load the lower xor byte from the table, xor zl and x3, store result in zl (=the new crc low value) +; move x4 (the new high byte) to x3, the crc value is ready +; + + +macro POP_STANDARD ; 18 cycles + pop ZH + pop ZL + 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] crc high byte + ldi x2, 1<<USBPLUS ;[6] [rx loop init] current line state is K state. D+=="1", D-=="0" + push x5 ;[7] + 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 +;-------------------------------------------------------------------------------------------------------------- + +; pid bit 0 - used for even more register saving (we need the z pointer) + in x1, USBIN ;[0] sample line state + andi x1, USBMASK ;[1] filter only D+ and D- bits + eor x2, x1 ;[2] generate inverted of actual bit + sbrc x2, USBMINUS ;[3] if the bit is set we received a zero + sec ;[4] + ror shift ;[5] we perform no unstuffing check here as this is the first bit + mov x2, x1 ;[6] + push ZL ;[7] + ;[8] + push ZH ;[9] + ;[10] + ldi x3, 0xFE ;[11] x3 is the high order crc value + + +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] + ldi ZL, 0x54 ;[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 x5 ;[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 x5, 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 x5, 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 x5, 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 x5, 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 +#define __USE_CRC__ +#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 + ldi ZH, hi8(usbCrcTableHigh);[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: + lpm x4, Z ;[8] load the higher crc xor-byte and store it for later use + ;[9] lpm needs 3 cycles + ;[10] + ldi ZH, hi8(usbCrcTableLow);[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: + lpm ZL, Z ;[7] load the lower xor crc byte + ;[8] lpm needs 3 cycles + ;[9] + eor ZL, x3 ;[10] xor the old high crc byte with the low xor-byte + mov x3, x4 ;[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 x5, shift ;[7] x5 marks all bits which have not been inverted by the unstuffing subs + mov x4, x5 ;[8] keep a copy of the data byte it will be stored during next bit0 + eor ZL, x4 ;[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 x5, 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 x5, 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 x5, 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 x5, 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 + +;-------------------------------------------------------------------------------------------------------------- +; The crc table follows. It has to be aligned to enable a fast loading of the needed bytes. +; There are two tables of 256 entries each, the low and the high byte table. +; Table values were generated with the following C code: +/* +#include <stdio.h> +int main (int argc, char **argv) +{ + int i, j; + for (i=0; i<512; i++){ + unsigned short crc = i & 0xff; + for(j=0; j<8; j++) crc = (crc >> 1) ^ ((crc & 1) ? 0xa001 : 0); + if((i & 7) == 0) printf("\n.byte "); + printf("0x%02x, ", (i > 0xff ? (crc >> 8) : crc) & 0xff); + if(i == 255) printf("\n"); + } + return 0; +} + +// Use the following algorithm to compute CRC values: +ushort computeCrc(uchar *msg, uchar msgLen) +{ + uchar i; + ushort crc = 0xffff; + for(i = 0; i < msgLen; i++) + crc = usbCrcTable16[lo8(crc) ^ msg[i]] ^ hi8(crc); + return crc; +} +*/ + +.balign 256 +usbCrcTableLow: +.byte 0x00, 0xC1, 0x81, 0x40, 0x01, 0xC0, 0x80, 0x41 +.byte 0x01, 0xC0, 0x80, 0x41, 0x00, 0xC1, 0x81, 0x40 +.byte 0x01, 0xC0, 0x80, 0x41, 0x00, 0xC1, 0x81, 0x40 +.byte 0x00, 0xC1, 0x81, 0x40, 0x01, 0xC0, 0x80, 0x41 +.byte 0x01, 0xC0, 0x80, 0x41, 0x00, 0xC1, 0x81, 0x40 +.byte 0x00, 0xC1, 0x81, 0x40, 0x01, 0xC0, 0x80, 0x41 +.byte 0x00, 0xC1, 0x81, 0x40, 0x01, 0xC0, 0x80, 0x41 +.byte 0x01, 0xC0, 0x80, 0x41, 0x00, 0xC1, 0x81, 0x40 +.byte 0x01, 0xC0, 0x80, 0x41, 0x00, 0xC1, 0x81, 0x40 +.byte 0x00, 0xC1, 0x81, 0x40, 0x01, 0xC0, 0x80, 0x41 +.byte 0x00, 0xC1, 0x81, 0x40, 0x01, 0xC0, 0x80, 0x41 +.byte 0x01, 0xC0, 0x80, 0x41, 0x00, 0xC1, 0x81, 0x40 +.byte 0x00, 0xC1, 0x81, 0x40, 0x01, 0xC0, 0x80, 0x41 +.byte 0x01, 0xC0, 0x80, 0x41, 0x00, 0xC1, 0x81, 0x40 +.byte 0x01, 0xC0, 0x80, 0x41, 0x00, 0xC1, 0x81, 0x40 +.byte 0x00, 0xC1, 0x81, 0x40, 0x01, 0xC0, 0x80, 0x41 +.byte 0x01, 0xC0, 0x80, 0x41, 0x00, 0xC1, 0x81, 0x40 +.byte 0x00, 0xC1, 0x81, 0x40, 0x01, 0xC0, 0x80, 0x41 +.byte 0x00, 0xC1, 0x81, 0x40, 0x01, 0xC0, 0x80, 0x41 +.byte 0x01, 0xC0, 0x80, 0x41, 0x00, 0xC1, 0x81, 0x40 +.byte 0x00, 0xC1, 0x81, 0x40, 0x01, 0xC0, 0x80, 0x41 +.byte 0x01, 0xC0, 0x80, 0x41, 0x00, 0xC1, 0x81, 0x40 +.byte 0x01, 0xC0, 0x80, 0x41, 0x00, 0xC1, 0x81, 0x40 +.byte 0x00, 0xC1, 0x81, 0x40, 0x01, 0xC0, 0x80, 0x41 +.byte 0x00, 0xC1, 0x81, 0x40, 0x01, 0xC0, 0x80, 0x41 +.byte 0x01, 0xC0, 0x80, 0x41, 0x00, 0xC1, 0x81, 0x40 +.byte 0x01, 0xC0, 0x80, 0x41, 0x00, 0xC1, 0x81, 0x40 +.byte 0x00, 0xC1, 0x81, 0x40, 0x01, 0xC0, 0x80, 0x41 +.byte 0x01, 0xC0, 0x80, 0x41, 0x00, 0xC1, 0x81, 0x40 +.byte 0x00, 0xC1, 0x81, 0x40, 0x01, 0xC0, 0x80, 0x41 +.byte 0x00, 0xC1, 0x81, 0x40, 0x01, 0xC0, 0x80, 0x41 +.byte 0x01, 0xC0, 0x80, 0x41, 0x00, 0xC1, 0x81, 0x40 + +; .balign 256 +usbCrcTableHigh: +.byte 0x00, 0xC0, 0xC1, 0x01, 0xC3, 0x03, 0x02, 0xC2 +.byte 0xC6, 0x06, 0x07, 0xC7, 0x05, 0xC5, 0xC4, 0x04 +.byte 0xCC, 0x0C, 0x0D, 0xCD, 0x0F, 0xCF, 0xCE, 0x0E +.byte 0x0A, 0xCA, 0xCB, 0x0B, 0xC9, 0x09, 0x08, 0xC8 +.byte 0xD8, 0x18, 0x19, 0xD9, 0x1B, 0xDB, 0xDA, 0x1A +.byte 0x1E, 0xDE, 0xDF, 0x1F, 0xDD, 0x1D, 0x1C, 0xDC +.byte 0x14, 0xD4, 0xD5, 0x15, 0xD7, 0x17, 0x16, 0xD6 +.byte 0xD2, 0x12, 0x13, 0xD3, 0x11, 0xD1, 0xD0, 0x10 +.byte 0xF0, 0x30, 0x31, 0xF1, 0x33, 0xF3, 0xF2, 0x32 +.byte 0x36, 0xF6, 0xF7, 0x37, 0xF5, 0x35, 0x34, 0xF4 +.byte 0x3C, 0xFC, 0xFD, 0x3D, 0xFF, 0x3F, 0x3E, 0xFE +.byte 0xFA, 0x3A, 0x3B, 0xFB, 0x39, 0xF9, 0xF8, 0x38 +.byte 0x28, 0xE8, 0xE9, 0x29, 0xEB, 0x2B, 0x2A, 0xEA +.byte 0xEE, 0x2E, 0x2F, 0xEF, 0x2D, 0xED, 0xEC, 0x2C +.byte 0xE4, 0x24, 0x25, 0xE5, 0x27, 0xE7, 0xE6, 0x26 +.byte 0x22, 0xE2, 0xE3, 0x23, 0xE1, 0x21, 0x20, 0xE0 +.byte 0xA0, 0x60, 0x61, 0xA1, 0x63, 0xA3, 0xA2, 0x62 +.byte 0x66, 0xA6, 0xA7, 0x67, 0xA5, 0x65, 0x64, 0xA4 +.byte 0x6C, 0xAC, 0xAD, 0x6D, 0xAF, 0x6F, 0x6E, 0xAE +.byte 0xAA, 0x6A, 0x6B, 0xAB, 0x69, 0xA9, 0xA8, 0x68 +.byte 0x78, 0xB8, 0xB9, 0x79, 0xBB, 0x7B, 0x7A, 0xBA +.byte 0xBE, 0x7E, 0x7F, 0xBF, 0x7D, 0xBD, 0xBC, 0x7C +.byte 0xB4, 0x74, 0x75, 0xB5, 0x77, 0xB7, 0xB6, 0x76 +.byte 0x72, 0xB2, 0xB3, 0x73, 0xB1, 0x71, 0x70, 0xB0 +.byte 0x50, 0x90, 0x91, 0x51, 0x93, 0x53, 0x52, 0x92 +.byte 0x96, 0x56, 0x57, 0x97, 0x55, 0x95, 0x94, 0x54 +.byte 0x9C, 0x5C, 0x5D, 0x9D, 0x5F, 0x9F, 0x9E, 0x5E +.byte 0x5A, 0x9A, 0x9B, 0x5B, 0x99, 0x59, 0x58, 0x98 +.byte 0x88, 0x48, 0x49, 0x89, 0x4B, 0x8B, 0x8A, 0x4A +.byte 0x4E, 0x8E, 0x8F, 0x4F, 0x8D, 0x4D, 0x4C, 0x8C +.byte 0x44, 0x84, 0x85, 0x45, 0x87, 0x47, 0x46, 0x86 +.byte 0x82, 0x42, 0x43, 0x83, 0x41, 0x81, 0x80, 0x40 + |