/* Name: usbdrvasm12.inc
* Project: V-USB, virtual USB port for Atmel's(r) AVR(r) microcontrollers
* Author: Christian Starkjohann
* Creation Date: 2004-12-29
* 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 12 MHz version of the asssembler part of the USB driver. It
requires a 12 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!
Timing constraints according to spec (in bit times):
timing subject min max CPUcycles
---------------------------------------------------------------------------
EOP of OUT/SETUP to sync pattern of DATA0 (both rx) 2 16 16-128
EOP of IN to sync pattern of DATA0 (rx, then tx) 2 7.5 16-60
DATAx (rx) to ACK/NAK/STALL (tx) 2 7.5 16-60
*/
;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: 34 cycles -> max 25 cycles interrupt disable
;max stack usage: [ret(2), YL, SREG, YH, shift, x1, x2, x3, cnt, x4] = 11 bytes
;Numbers in brackets are maximum cycles since SOF.
USB_INTR_VECTOR:
;order of registers pushed: YL, SREG [sofError], YH, shift, x1, x2, x3, cnt
push YL ;2 [35] push only what is necessary to sync with edge ASAP
in YL, SREG ;1 [37]
push YL ;2 [39]
;----------------------------------------------------------------------------
; 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
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:
;{3, 5} after falling D- edge, average delay: 4 cycles [we want 4 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 YH ;2 [2]
lds YL, usbInputBufOffset;2 [4]
clr YH ;1 [5]
subi YL, lo8(-(usbRxBuf));1 [6]
sbci YH, hi8(-(usbRxBuf));1 [7]
sbis USBIN, USBMINUS ;1 [8] we want two bits K [sample 1 cycle too early]
rjmp haveTwoBitsK ;2 [10]
pop YH ;2 [11] undo the push from before
rjmp waitForK ;2 [13] this was not the end of sync, retry
haveTwoBitsK:
;----------------------------------------------------------------------------
; push more registers and initialize values while we sample the first bits:
;----------------------------------------------------------------------------
push shift ;2 [16]
push x1 ;2 [12]
push x2 ;2 [14]
in x1, USBIN ;1 [17] <-- sample bit 0
ldi shift, 0xff ;1 [18]
bst x1, USBMINUS ;1 [19]
bld shift, 0 ;1 [20]
push x3 ;2 [22]
push cnt ;2 [24]
in x2, USBIN ;1 [25] <-- sample bit 1
ser x3 ;1 [26] [inserted init instruction]
eor x1, x2 ;1 [27]
bst x1, USBMINUS ;1 [28]
bld shift, 1 ;1 [29]
ldi cnt, USB_BUFSIZE;1 [30] [inserted init instruction]
rjmp rxbit2 ;2 [32]
;----------------------------------------------------------------------------
; Receiver loop (numbers in brackets are cycles within byte after instr)
;----------------------------------------------------------------------------
unstuff0: ;1 (branch taken)
andi x3, ~0x01 ;1 [15]
mov x1, x2 ;1 [16] x2 contains last sampled (stuffed) bit
in x2, USBIN ;1 [17] <-- sample bit 1 again
ori shift, 0x01 ;1 [18]
rjmp didUnstuff0 ;2 [20]
unstuff1: ;1 (branch taken)
mov x2, x1 ;1 [21] x1 contains last sampled (stuffed) bit
andi x3, ~0x02 ;1 [22]
ori shift, 0x02 ;1 [23]
nop ;1 [24]
in x1, USBIN ;1 [25] <-- sample bit 2 again
rjmp didUnstuff1 ;2 [27]
unstuff2: ;1 (branch taken)
andi x3, ~0x04 ;1 [29]
ori shift, 0x04 ;1 [30]
mov x1, x2 ;1 [31] x2 contains last sampled (stuffed) bit
nop ;1 [32]
in x2, USBIN ;1 [33] <-- sample bit 3
rjmp didUnstuff2 ;2 [35]
unstuff3: ;1 (branch taken)
in x2, USBIN ;1 [34] <-- sample stuffed bit 3 [one cycle too late]
andi x3, ~0x08 ;1 [35]
ori shift, 0x08 ;1 [36]
rjmp didUnstuff3 ;2 [38]
unstuff4: ;1 (branch taken)
andi x3, ~0x10 ;1 [40]
in x1, USBIN ;1 [41] <-- sample stuffed bit 4
ori shift, 0x10 ;1 [42]
rjmp didUnstuff4 ;2 [44]
unstuff5: ;1 (branch taken)
andi x3, ~0x20 ;1 [48]
in x2, USBIN ;1 [49] <-- sample stuffed bit 5
ori shift, 0x20 ;1 [50]
rjmp didUnstuff5 ;2 [52]
unstuff6: ;1 (branch taken)
andi x3, ~0x40 ;1 [56]
in x1, USBIN ;1 [57] <-- sample stuffed bit 6
ori shift, 0x40 ;1 [58]
rjmp didUnstuff6 ;2 [60]
; extra jobs done during bit interval:
; bit 0: store, clear [SE0 is unreliable here due to bit dribbling in hubs]
; bit 1: se0 check
; bit 2: overflow check
; bit 3: recovery from delay [bit 0 tasks took too long]
; bit 4: none
; bit 5: none
; bit 6: none
; bit 7: jump, eor
rxLoop:
eor x3, shift ;1 [0] reconstruct: x3 is 0 at bit locations we changed, 1 at others
in x1, USBIN ;1 [1] <-- sample bit 0
st y+, x3 ;2 [3] store data
ser x3 ;1 [4]
nop ;1 [5]
eor x2, x1 ;1 [6]
bst x2, USBMINUS;1 [7]
bld shift, 0 ;1 [8]
in x2, USBIN ;1 [9] <-- sample bit 1 (or possibly bit 0 stuffed)
andi x2, USBMASK ;1 [10]
breq se0 ;1 [11] SE0 check for bit 1
andi shift, 0xf9 ;1 [12]
didUnstuff0:
breq unstuff0 ;1 [13]
eor x1, x2 ;1 [14]
bst x1, USBMINUS;1 [15]
bld shift, 1 ;1 [16]
rxbit2:
in x1, USBIN ;1 [17] <-- sample bit 2 (or possibly bit 1 stuffed)
andi shift, 0xf3 ;1 [18]
breq unstuff1 ;1 [19] do remaining work for bit 1
didUnstuff1:
subi cnt, 1 ;1 [20]
brcs overflow ;1 [21] loop control
eor x2, x1 ;1 [22]
bst x2, USBMINUS;1 [23]
bld shift, 2 ;1 [24]
in x2, USBIN ;1 [25] <-- sample bit 3 (or possibly bit 2 stuffed)
andi shift, 0xe7 ;1 [26]
breq unstuff2 ;1 [27]
didUnstuff2:
eor x1, x2 ;1 [28]
bst x1, USBMINUS;1 [29]
bld shift, 3 ;1 [30]
didUnstuff3:
andi shift, 0xcf ;1 [31]
breq unstuff3 ;1 [32]
in x1, USBIN ;1 [33] <-- sample bit 4
eor x2, x1 ;1 [34]
bst x2, USBMINUS;1 [35]
bld shift, 4 ;1 [36]
didUnstuff4:
andi shift, 0x9f ;1 [37]
breq unstuff4 ;1 [38]
nop2 ;2 [40]
in x2, USBIN ;1 [41] <-- sample bit 5
eor x1, x2 ;1 [42]
bst x1, USBMINUS;1 [43]
bld shift, 5 ;1 [44]
didUnstuff5:
andi shift, 0x3f ;1 [45]
breq unstuff5 ;1 [46]
nop2 ;2 [48]
in x1, USBIN ;1 [49] <-- sample bit 6
eor x2, x1 ;1 [50]
bst x2, USBMINUS;1 [51]
bld shift, 6 ;1 [52]
didUnstuff6:
cpi shift, 0x02 ;1 [53]
brlo unstuff6 ;1 [54]
nop2 ;2 [56]
in x2, USBIN ;1 [57] <-- sample bit 7
eor x1, x2 ;1 [58]
bst x1, USBMINUS;1 [59]
bld shift, 7 ;1 [60]
didUnstuff7:
cpi shift, 0x04 ;1 [61]
brsh rxLoop ;2 [63] loop control
unstuff7:
andi x3, ~0x80 ;1 [63]
ori shift, 0x80 ;1 [64]
in x2, USBIN ;1 [65] <-- sample stuffed bit 7
nop ;1 [66]
rjmp didUnstuff7 ;2 [68]
macro POP_STANDARD ; 12 cycles
pop cnt
pop x3
pop x2
pop x1
pop shift
pop YH
endm
macro POP_RETI ; 5 cycles
pop YL
out SREG, YL
pop YL
endm
#include "asmcommon.inc"
;----------------------------------------------------------------------------
; Transmitting data
;----------------------------------------------------------------------------
txByteLoop:
txBitloop:
stuffN1Delay: ; [03]
ror shift ;[-5] [11] [59]
brcc doExorN1 ;[-4] [60]
subi x4, 1 ;[-3]
brne commonN1 ;[-2]
lsl shift ;[-1] compensate ror after rjmp stuffDelay
nop ;[00] stuffing consists of just waiting 8 cycles
rjmp stuffN1Delay ;[01] after ror, C bit is reliably clear
sendNakAndReti: ;0 [-19] 19 cycles until SOP
ldi x3, USBPID_NAK ;1 [-18]
rjmp usbSendX3 ;2 [-16]
sendAckAndReti: ;0 [-19] 19 cycles until SOP
ldi x3, USBPID_ACK ;1 [-18]
rjmp usbSendX3 ;2 [-16]
sendCntAndReti: ;0 [-17] 17 cycles until SOP
mov x3, cnt ;1 [-16]
usbSendX3: ;0 [-16]
ldi YL, 20 ;1 [-15] 'x3' is R20
ldi YH, 0 ;1 [-14]
ldi cnt, 2 ;1 [-13]
; 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' -- including sync byte
;uses: x1...x2, x4, shift, cnt, Y [x1 = mirror USBOUT, x2 = USBMASK, x4 = bitstuff cnt]
;Numbers in brackets are time since first bit of sync pattern is sent (start of instruction)
usbSendAndReti:
in x2, USBDDR ;[-12] 12 cycles until SOP
ori x2, USBMASK ;[-11]
sbi USBOUT, USBMINUS ;[-10] prepare idle state; D+ and D- must have been 0 (no pullups)
out USBDDR, x2 ;[-8] <--- acquire bus
in x1, USBOUT ;[-7] port mirror for tx loop
ldi shift, 0x40 ;[-6] sync byte is first byte sent (we enter loop after ror)
ldi x2, USBMASK ;[-5]
push x4 ;[-4]
doExorN1:
eor x1, x2 ;[-2] [06] [62]
ldi x4, 6 ;[-1] [07] [63]
commonN1:
stuffN2Delay:
out USBOUT, x1 ;[00] [08] [64] <--- set bit
ror shift ;[01]
brcc doExorN2 ;[02]
subi x4, 1 ;[03]
brne commonN2 ;[04]
lsl shift ;[05] compensate ror after rjmp stuffDelay
rjmp stuffN2Delay ;[06] after ror, C bit is reliably clear
doExorN2:
eor x1, x2 ;[04] [12]
ldi x4, 6 ;[05] [13]
commonN2:
nop ;[06] [14]
subi cnt, 171 ;[07] [15] trick: (3 * 171) & 0xff = 1
out USBOUT, x1 ;[08] [16] <--- set bit
brcs txBitloop ;[09] [25] [41]
stuff6Delay:
ror shift ;[42] [50]
brcc doExor6 ;[43]
subi x4, 1 ;[44]
brne common6 ;[45]
lsl shift ;[46] compensate ror after rjmp stuffDelay
nop ;[47] stuffing consists of just waiting 8 cycles
rjmp stuff6Delay ;[48] after ror, C bit is reliably clear
doExor6:
eor x1, x2 ;[45] [53]
ldi x4, 6 ;[46]
common6:
stuff7Delay:
ror shift ;[47] [55]
out USBOUT, x1 ;[48] <--- set bit
brcc doExor7 ;[49]
subi x4, 1 ;[50]
brne common7 ;[51]
lsl shift ;[52] compensate ror after rjmp stuffDelay
rjmp stuff7Delay ;[53] after ror, C bit is reliably clear
doExor7:
eor x1, x2 ;[51] [59]
ldi x4, 6 ;[52]
common7:
ld shift, y+ ;[53]
tst cnt ;[55]
out USBOUT, x1 ;[56] <--- set bit
brne txByteLoop ;[57]
;make SE0:
cbr x1, USBMASK ;[58] prepare SE0 [spec says EOP may be 15 to 18 cycles]
lds x2, usbNewDeviceAddr;[59]
lsl x2 ;[61] we compare with left shifted address
subi YL, 2 + 20 ;[62] Only assign address on data packets, not ACK/NAK in x3
sbci YH, 0 ;[63]
out USBOUT, x1 ;[00] <-- out SE0 -- from now 2 bits = 16 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
breq skipAddrAssign ;[01]
sts usbDeviceAddr, x2 ; if not skipped: SE0 is one cycle longer
skipAddrAssign:
;end of usbDeviceAddress transfer
ldi x2, 1<<USB_INTR_PENDING_BIT;[03] int0 occurred during TX -- clear pending flag
USB_STORE_PENDING(x2) ;[04]
ori x1, USBIDLE ;[05]
in x2, USBDDR ;[06]
cbr x2, USBMASK ;[07] set both pins to input
mov x3, x1 ;[08]
cbr x3, USBMASK ;[09] configure no pullup on both pins
pop x4 ;[10]
nop2 ;[12]
nop2 ;[14]
out USBOUT, x1 ;[16] <-- out J (idle) -- end of SE0 (EOP signal)
out USBDDR, x2 ;[17] <-- release bus now
out USBOUT, x3 ;[18] <-- ensure no pull-up resistors are active
rjmp doReturn
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