or      phase, r0       ;[025]    subi    cnt, 1          ;[026] overflow check    brcs    overflow        ;[027]    in      r0, USBIN       ;[028] <-- phase    eor     x2, x1          ;[029]    bst     x2, USBMINUS    ;[030]    bld     shift, 2        ;[031]    andi    shift, 0xe7     ;[032]didUnstuff2:                ;[   ]    in      x2, USBIN       ;[033] <-- bit 3    breq    unstuff2        ;[034] *** unstuff escape    eor     r0, x2          ;[035]    or      phase, r0       ;[036]    eor     x1, x2          ;[037]    bst     x1, USBMINUS    ;[038]    in      r0, USBIN       ;[039] <-- phase    bld     shift, 3        ;[040]    andi    shift, 0xcf     ;[041]didUnstuff3:                ;[   ]    breq    unstuff3        ;[042] *** unstuff escape    nop                     ;[043]    in      x1, USBIN       ;[044] <-- bit 4    eor     x2, x1          ;[045]    bst     x2, USBMINUS    ;[046]    bld     shift, 4        ;[047]didUnstuff4:                ;[   ]    eor     r0, x1          ;[048]    or      phase, r0       ;[049]    in      r0, USBIN       ;[050] <-- phase    andi    shift, 0x9f     ;[051]    breq    unstuff4        ;[052] *** unstuff escape    rjmp    continueWithBit5;[053];   [---]                   ;[054];----------------------------------------------------------------------------; Processing of received packet (numbers in brackets are cycles after center of SE0);----------------------------------------------------------------------------;This is the only non-error exit point for the software receiver loop;we don't check any CRCs here because there is no time left.#define token   x1se0:    subi    cnt, USB_BUFSIZE    ;[5]    neg     cnt                 ;[6]    cpi     cnt, 3              ;[7]    ldi     x2, 1<<USB_INTR_PENDING_BIT ;[8]    out     USB_INTR_PENDING, x2;[9] clear pending intr and check flag later. SE0 should be over.    brlo    doReturn            ;[10] this is probably an ACK, NAK or similar packet    sub     YL, cnt             ;[11]    sbci    YH, 0               ;[12]    ld      token, y            ;[13]    cpi     token, USBPID_DATA0 ;[15]    breq    handleData          ;[16]    cpi     token, USBPID_DATA1 ;[17]    breq    handleData          ;[18]    ldd     x2, y+1             ;[19] ADDR and 1 bit endpoint number    mov     x3, x2              ;[21] store for endpoint number    andi    x2, 0x7f            ;[22] x2 is now ADDR    lds     shift, usbDeviceAddr;[23]    cp      x2, shift           ;[25]overflow:                       ; This is a hack: brcs overflow will never have Z flag set    brne    ignorePacket        ;[26] packet for different address    cpi     token, USBPID_IN    ;[27]    breq    handleIn            ;[28]    cpi     token, USBPID_SETUP ;[29]    breq    handleSetupOrOut    ;[30]    cpi     token, USBPID_OUT   ;[31]    breq    handleSetupOrOut    ;[32];   rjmp    ignorePacket        ;fallthrough, should not happen anyway.ignorePacket:    clr     shift    sts     usbCurrentTok, shiftdoReturn:    pop     cnt    pop     x4    pop     x3    pop     x2    pop     x1    pop     shift    pop     YH    pop     YLsofError:    pop     r0    out     SREG, r0    pop     r0    reti#if USB_CFG_HAVE_INTRIN_ENDPOINT && USB_CFG_HAVE_INTRIN_ENDPOINT3handleIn3:    lds     cnt, usbTxLen3      ;[43]    sbrc    cnt, 4              ;[45]    rjmp    sendCntAndReti      ;[46] 48 + 16 = 64 until SOP    sts     usbTxLen3, x1       ;[47] x1 == USBPID_NAK from above    ldi     YL, lo8(usbTxBuf3)  ;[49]    ldi     YH, hi8(usbTxBuf3)  ;[50]    rjmp    usbSendAndReti      ;[51] 53 + 12 = 65 until SOP#endif;Setup and Out are followed by a data packet two bit times (16 cycles) after;the end of SE0. The sync code allows up to 40 cycles delay from the start of;the sync pattern until the first bit is sampled. That's a total of 56 cycles.handleSetupOrOut:               ;[34]#if USB_CFG_IMPLEMENT_FN_WRITEOUT   /* if we have data for second OUT endpoint, set usbCurrentTok to -1 */    sbrc    x3, 7               ;[34] skip if endpoint 0    ldi     token, -1           ;[35] indicate that this is endpoint 1 OUT#endif    sts     usbCurrentTok, token;[36]    pop     cnt                 ;[38]    pop     x4                  ;[40]    pop     x3                  ;[42]    pop     x2                  ;[44]    pop     x1                  ;[46]    pop     shift               ;[48]    pop     YH                  ;[50]    pop     YL                  ;[52]    in      r0, USB_INTR_PENDING;[54]    sbrc    r0, USB_INTR_PENDING_BIT;[55] check whether data is already arriving    rjmp    waitForJ            ;[56] save the pops and pushes -- a new interrupt is aready pending    rjmp    sofError            ;[57] not an error, but it does the pops and reti we wanthandleData:    lds     token, usbCurrentTok;[20]    tst     token               ;[22]    breq    doReturn            ;[23]    lds     x2, usbRxLen        ;[24]    tst     x2                  ;[26]    brne    sendNakAndReti      ;[27]; 2006-03-11: The following two lines fix a problem where the device was not; recognized if usbPoll() was called less frequently than once every 4 ms.    cpi     cnt, 4              ;[28] zero sized data packets are status phase only -- ignore and ack    brmi    sendAckAndReti      ;[29] keep rx buffer clean -- we must not NAK next SETUP    sts     usbRxLen, cnt       ;[30] store received data, swap buffers    sts     usbRxToken, token   ;[32]    lds     x2, usbInputBufOffset;[34] swap buffers    ldi     cnt, USB_BUFSIZE    ;[36]    sub     cnt, x2             ;[37]    sts     usbInputBufOffset, cnt;[38] buffers now swapped    rjmp    sendAckAndReti      ;[40] 42 + 17 = 59 until SOPhandleIn:;We don't send any data as long as the C code has not processed the current;input data and potentially updated the output data. That's more efficient;in terms of code size than clearing the tx buffers when a packet is received.    lds     x1, usbRxLen        ;[30]    cpi     x1, 1               ;[32] negative values are flow control, 0 means "buffer free"    brge    sendNakAndReti      ;[33] unprocessed input packet?    ldi     x1, USBPID_NAK      ;[34] prepare value for usbTxLen#if USB_CFG_HAVE_INTRIN_ENDPOINT    sbrc    x3, 7               ;[35] x3 contains addr + endpoint    rjmp    handleIn1           ;[36]#endif    lds     cnt, usbTxLen       ;[37]    sbrc    cnt, 4              ;[39] all handshake tokens have bit 4 set    rjmp    sendCntAndReti      ;[40] 42 + 16 = 58 until SOP    sts     usbTxLen, x1        ;[41] x1 == USBPID_NAK from above    ldi     YL, lo8(usbTxBuf)   ;[43]    ldi     YH, hi8(usbTxBuf)   ;[44]    rjmp    usbSendAndReti      ;[45] 47 + 12 = 59 until SOP; Comment about when to set usbTxLen to USBPID_NAK:; We should set it back 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 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.#if USB_CFG_HAVE_INTRIN_ENDPOINT    /* placed here due to relative jump range */handleIn1:                      ;[38]#if USB_CFG_HAVE_INTRIN_ENDPOINT3; 2006-06-10 as suggested by O.Tamura: support second INTR IN / BULK IN endpoint    ldd     x2, y+2             ;[38]    sbrc    x2, 0               ;[40]    rjmp    handleIn3           ;[41]#endif    lds     cnt, usbTxLen1      ;[42]    sbrc    cnt, 4              ;[44] all handshake tokens have bit 4 set    rjmp    sendCntAndReti      ;[45] 47 + 16 = 63 until SOP    sts     usbTxLen1, x1       ;[46] x1 == USBPID_NAK from above    ldi     YL, lo8(usbTxBuf1)  ;[48]    ldi     YH, hi8(usbTxBuf1)  ;[49]    rjmp    usbSendAndReti      ;[50] 52 + 12 + 64 until SOP#endif; 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 repliesbitstuff7:    eor     x1, x4          ;[4]    ldi     x2, 0           ;[5]    nop2                    ;[6] C is zero (brcc)    rjmp    didStuff7       ;[8]bitstuffN:    eor     x1, x4          ;[5]    ldi     x2, 0           ;[6]    lpm                     ;[7] 3 cycle NOP, modifies r0    out     USBOUT, x1      ;[10] <-- out    rjmp    didStuffN       ;[0]#define bitStatus   x3sendNakAndReti:    ldi     cnt, USBPID_NAK ;[-19]    rjmp    sendCntAndReti  ;[-18]sendAckAndReti:    ldi     cnt, USBPID_ACK ;[-17]sendCntAndReti:    mov     r0, cnt         ;[-16]    ldi     YL, 0           ;[-15] R0 address is 0    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, shift, cnt, Y;Numbers in brackets are time since first bit of sync pattern is sentusbSendAndReti:             ; 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      ;[-7] <- acquire bus; need not init x2 (bitstuff history) because sync starts with 0    ldi     x4, USBMASK     ;[-6] exor mask    ldi     shift, 0x80     ;[-5] sync byte is first byte sent    ldi     bitStatus, 0xff ;[-4] init bit loop counter, works for up to 12 bytesbyteloop:bitloop:    sbrs    shift, 0        ;[8] [-3]    eor     x1, x4          ;[9] [-2]    out     USBOUT, x1      ;[10] [-1] <-- out    ror     shift           ;[0]    ror     x2              ;[1]didStuffN:    cpi     x2, 0xfc        ;[2]    brcc    bitstuffN       ;[3]    nop                     ;[4]    subi    bitStatus, 37   ;[5] 256 / 7 ~=~ 37    brcc    bitloop         ;[6] when we leave the loop, bitStatus has almost the initial value    sbrs    shift, 0        ;[7]    eor     x1, x4          ;[8]    ror     shift           ;[9]didStuff7:    out     USBOUT, x1      ;[10] <-- out    ror     x2              ;[0]    cpi     x2, 0xfc        ;[1]    brcc    bitstuff7       ;[2]    ld      shift, y+       ;[3]    dec     cnt             ;[5]    brne    byteloop        ;[6];make SE0:    cbr     x1, USBMASK     ;[7] prepare SE0 [spec says EOP may be 21 to 25 cycles]    lds     x2, usbNewDeviceAddr;[8]    out     USBOUT, x1      ;[10] <-- out SE0 -- from now 2 bits = 22 cycles until bus idle;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    subi    YL, 2           ;[0]    sbci    YH, 0           ;[1]    breq    skipAddrAssign  ;[2]    sts     usbDeviceAddr, x2; if not skipped: SE0 is one cycle longerskipAddrAssign:;end of usbDeviceAddress transfer    ldi     x2, 1<<USB_INTR_PENDING_BIT;[4] int0 occurred during TX -- clear pending flag    out     USB_INTR_PENDING, x2;[5]    ori     x1, USBIDLE     ;[6]    in      x2, USBDDR      ;[7]    cbr     x2, USBMASK     ;[8] set both pins to input    mov     x3, x1          ;[9]    cbr     x3, USBMASK     ;[10] configure no pullup on both pins    ldi     x4, 4           ;[11]se0Delay:    dec     x4              ;[12] [15] [18] [21]    brne    se0Delay        ;[13] [16] [19] [22]    out     USBOUT, x1      ;[23] <-- out J (idle) -- end of SE0 (EOP signal)    out     USBDDR, x2      ;[24] <-- release bus now    out     USBOUT, x3      ;[25] <-- ensure no pull-up resistors are active    rjmp    doReturn