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+/* Name: usbdrvasm165.inc
+ * Project: V-USB, virtual USB port for Atmel's(r) AVR(r) microcontrollers
+ * Author: Christian Starkjohann
+ * Creation Date: 2007-04-22
+ * Tabsize: 4
+ * Copyright: (c) 2007 by 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 16.5 MHz version of the USB driver. It is intended for the
+ATTiny45 and similar controllers running on 16.5 MHz internal RC oscillator.
+This version contains a phase locked loop in the receiver routine to cope with
+slight clock rate deviations of up to +/- 1%.
+
+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!
+*/
+
+;Software-receiver engine. Strict timing! Don't change unless you can preserve timing!
+;interrupt response time: 4 cycles + insn running = 7 max if interrupts always enabled
+;max allowable interrupt latency: 59 cycles -> max 52 cycles interrupt disable
+;max stack usage: [ret(2), r0, SREG, YL, YH, shift, x1, x2, x3, x4, cnt] = 12 bytes
+;nominal frequency: 16.5 MHz -> 11 cycles per bit
+; 16.3125 MHz < F_CPU < 16.6875 MHz (+/- 1.1%)
+; Numbers in brackets are clocks counted from center of last sync bit
+; when instruction starts
+
+
+USB_INTR_VECTOR:
+;order of registers pushed: YL, SREG [sofError], r0, YH, shift, x1, x2, x3, x4, cnt
+ push YL ;[-23] push only what is necessary to sync with edge ASAP
+ in YL, SREG ;[-21]
+ push YL ;[-20]
+;----------------------------------------------------------------------------
+; 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 ;[-15]
+ rjmp foundK ;[-14]
+ 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: ;[-12]
+;{3, 5} after falling D- edge, average delay: 4 cycles [we want 5 for center sampling]
+;we have 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 r0 ;[-12]
+; [---] ;[-11]
+ push YH ;[-10]
+; [---] ;[-9]
+ lds YL, usbInputBufOffset;[-8]
+; [---] ;[-7]
+ clr YH ;[-6]
+ subi YL, lo8(-(usbRxBuf));[-5] [rx loop init]
+ sbci YH, hi8(-(usbRxBuf));[-4] [rx loop init]
+ mov r0, x2 ;[-3] [rx loop init]
+ sbis USBIN, USBMINUS ;[-2] we want two bits K (sample 2 cycles too early)
+ rjmp haveTwoBitsK ;[-1]
+ pop YH ;[0] undo the pushes from before
+ pop r0 ;[2]
+ rjmp waitForK ;[4] this was not the end of sync, retry
+; The entire loop from waitForK until rjmp waitForK above must not exceed two
+; bit times (= 22 cycles).
+
+;----------------------------------------------------------------------------
+; push more registers and initialize values while we sample the first bits:
+;----------------------------------------------------------------------------
+haveTwoBitsK: ;[1]
+ push shift ;[1]
+ push x1 ;[3]
+ push x2 ;[5]
+ push x3 ;[7]
+ ldi shift, 0xff ;[9] [rx loop init]
+ ori x3, 0xff ;[10] [rx loop init] == ser x3, clear zero flag
+
+ in x1, USBIN ;[11] <-- sample bit 0
+ bst x1, USBMINUS ;[12]
+ bld shift, 0 ;[13]
+ push x4 ;[14] == phase
+; [---] ;[15]
+ push cnt ;[16]
+; [---] ;[17]
+ ldi phase, 0 ;[18] [rx loop init]
+ ldi cnt, USB_BUFSIZE;[19] [rx loop init]
+ rjmp rxbit1 ;[20]
+; [---] ;[21]
+
+;----------------------------------------------------------------------------
+; Receiver loop (numbers in brackets are cycles within byte after instr)
+;----------------------------------------------------------------------------
+/*
+byte oriented operations done during loop:
+bit 0: store data
+bit 1: SE0 check
+bit 2: overflow check
+bit 3: catch up
+bit 4: rjmp to achieve conditional jump range
+bit 5: PLL
+bit 6: catch up
+bit 7: jump, fixup bitstuff
+; 87 [+ 2] cycles
+------------------------------------------------------------------
+*/
+continueWithBit5:
+ in x2, USBIN ;[055] <-- bit 5
+ eor r0, x2 ;[056]
+ or phase, r0 ;[057]
+ sbrc phase, USBMINUS ;[058]
+ lpm ;[059] optional nop3; modifies r0
+ in phase, USBIN ;[060] <-- phase
+ eor x1, x2 ;[061]
+ bst x1, USBMINUS ;[062]
+ bld shift, 5 ;[063]
+ andi shift, 0x3f ;[064]
+ in x1, USBIN ;[065] <-- bit 6
+ breq unstuff5 ;[066] *** unstuff escape
+ eor phase, x1 ;[067]
+ eor x2, x1 ;[068]
+ bst x2, USBMINUS ;[069]
+ bld shift, 6 ;[070]
+didUnstuff6: ;[ ]
+ in r0, USBIN ;[071] <-- phase
+ cpi shift, 0x02 ;[072]
+ brlo unstuff6 ;[073] *** unstuff escape
+didUnstuff5: ;[ ]
+ nop2 ;[074]
+; [---] ;[075]
+ in x2, USBIN ;[076] <-- bit 7
+ eor x1, x2 ;[077]
+ bst x1, USBMINUS ;[078]
+ bld shift, 7 ;[079]
+didUnstuff7: ;[ ]
+ eor r0, x2 ;[080]
+ or phase, r0 ;[081]
+ in r0, USBIN ;[082] <-- phase
+ cpi shift, 0x04 ;[083]
+ brsh rxLoop ;[084]
+; [---] ;[085]
+unstuff7: ;[ ]
+ andi x3, ~0x80 ;[085]
+ ori shift, 0x80 ;[086]
+ in x2, USBIN ;[087] <-- sample stuffed bit 7
+ nop ;[088]
+ rjmp didUnstuff7 ;[089]
+; [---] ;[090]
+ ;[080]
+
+unstuff5: ;[067]
+ eor phase, x1 ;[068]
+ andi x3, ~0x20 ;[069]
+ ori shift, 0x20 ;[070]
+ in r0, USBIN ;[071] <-- phase
+ mov x2, x1 ;[072]
+ nop ;[073]
+ nop2 ;[074]
+; [---] ;[075]
+ in x1, USBIN ;[076] <-- bit 6
+ eor r0, x1 ;[077]
+ or phase, r0 ;[078]
+ eor x2, x1 ;[079]
+ bst x2, USBMINUS ;[080]
+ bld shift, 6 ;[081] no need to check bitstuffing, we just had one
+ in r0, USBIN ;[082] <-- phase
+ rjmp didUnstuff5 ;[083]
+; [---] ;[084]
+ ;[074]
+
+unstuff6: ;[074]
+ andi x3, ~0x40 ;[075]
+ in x1, USBIN ;[076] <-- bit 6 again
+ ori shift, 0x40 ;[077]
+ nop2 ;[078]
+; [---] ;[079]
+ rjmp didUnstuff6 ;[080]
+; [---] ;[081]
+ ;[071]
+
+unstuff0: ;[013]
+ eor r0, x2 ;[014]
+ or phase, r0 ;[015]
+ andi x2, USBMASK ;[016] check for SE0
+ in r0, USBIN ;[017] <-- phase
+ breq didUnstuff0 ;[018] direct jump to se0 would be too long
+ andi x3, ~0x01 ;[019]
+ ori shift, 0x01 ;[020]
+ mov x1, x2 ;[021] mov existing sample
+ in x2, USBIN ;[022] <-- bit 1 again
+ rjmp didUnstuff0 ;[023]
+; [---] ;[024]
+ ;[014]
+
+unstuff1: ;[024]
+ eor r0, x1 ;[025]
+ or phase, r0 ;[026]
+ andi x3, ~0x02 ;[027]
+ in r0, USBIN ;[028] <-- phase
+ ori shift, 0x02 ;[029]
+ mov x2, x1 ;[030]
+ rjmp didUnstuff1 ;[031]
+; [---] ;[032]
+ ;[022]
+
+unstuff2: ;[035]
+ eor r0, x2 ;[036]
+ or phase, r0 ;[037]
+ andi x3, ~0x04 ;[038]
+ in r0, USBIN ;[039] <-- phase
+ ori shift, 0x04 ;[040]
+ mov x1, x2 ;[041]
+ rjmp didUnstuff2 ;[042]
+; [---] ;[043]
+ ;[033]
+
+unstuff3: ;[043]
+ in x2, USBIN ;[044] <-- bit 3 again
+ eor r0, x2 ;[045]
+ or phase, r0 ;[046]
+ andi x3, ~0x08 ;[047]
+ ori shift, 0x08 ;[048]
+ nop ;[049]
+ in r0, USBIN ;[050] <-- phase
+ rjmp didUnstuff3 ;[051]
+; [---] ;[052]
+ ;[042]
+
+unstuff4: ;[053]
+ andi x3, ~0x10 ;[054]
+ in x1, USBIN ;[055] <-- bit 4 again
+ ori shift, 0x10 ;[056]
+ rjmp didUnstuff4 ;[057]
+; [---] ;[058]
+ ;[048]
+
+rxLoop: ;[085]
+ eor x3, shift ;[086] reconstruct: x3 is 0 at bit locations we changed, 1 at others
+ in x1, USBIN ;[000] <-- bit 0
+ st y+, x3 ;[001]
+; [---] ;[002]
+ eor r0, x1 ;[003]
+ or phase, r0 ;[004]
+ eor x2, x1 ;[005]
+ in r0, USBIN ;[006] <-- phase
+ ser x3 ;[007]
+ bst x2, USBMINUS ;[008]
+ bld shift, 0 ;[009]
+ andi shift, 0xf9 ;[010]
+rxbit1: ;[ ]
+ in x2, USBIN ;[011] <-- bit 1
+ breq unstuff0 ;[012] *** unstuff escape
+ andi x2, USBMASK ;[013] SE0 check for bit 1
+didUnstuff0: ;[ ] Z only set if we detected SE0 in bitstuff
+ breq se0 ;[014]
+ eor r0, x2 ;[015]
+ or phase, r0 ;[016]
+ in r0, USBIN ;[017] <-- phase
+ eor x1, x2 ;[018]
+ bst x1, USBMINUS ;[019]
+ bld shift, 1 ;[020]
+ andi shift, 0xf3 ;[021]
+didUnstuff1: ;[ ]
+ in x1, USBIN ;[022] <-- bit 2
+ breq unstuff1 ;[023] *** unstuff escape
+ eor r0, x1 ;[024]
+ 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]
+
+macro POP_STANDARD ; 16 cycles
+ pop cnt
+ pop x4
+ pop x3
+ pop x2
+ pop x1
+ pop shift
+ pop YH
+ pop r0
+ endm
+macro POP_RETI ; 5 cycles
+ pop YL
+ out SREG, YL
+ pop YL
+ endm
+
+#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
+
+bitstuff7:
+ 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 x3
+
+sendNakAndReti:
+ 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 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 ;[-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 bytes
+byteloop:
+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]
+ lsl x2 ;[10] we compare with left shifted address
+ out USBOUT, x1 ;[11] <-- 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] Only assign address on data packets, not ACK/NAK in r0
+ sbci YH, 0 ;[1]
+ breq skipAddrAssign ;[2]
+ sts usbDeviceAddr, x2; if not skipped: SE0 is one cycle longer
+skipAddrAssign:
+;end of usbDeviceAddress transfer
+ ldi x2, 1<<USB_INTR_PENDING_BIT;[4] int0 occurred during TX -- clear pending flag
+ USB_STORE_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
+
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