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/* Name: usbdrvasm16.inc
* Project: V-USB, virtual USB port for Atmel's(r) AVR(r) microcontrollers
* Author: Christian Starkjohann
* Creation Date: 2007-06-15
* Tabsize: 4
* Copyright: (c) 2007 by OBJECTIVE DEVELOPMENT Software GmbH
* License: GNU GPL v2 (see License.txt), GNU GPL v3 or proprietary (CommercialLicense.txt)
* Revision: $Id: usbdrvasm16.inc 760 2009-08-09 18:59:43Z cs $
*/
/* Do not link this file! Link usbdrvasm.S instead, which includes the
* appropriate implementation!
*/
/*
General Description:
This file is the 16 MHz version of the asssembler part of the USB driver. It
requires a 16 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, bitcnt, shift, x1, x2, x3, x4, cnt] = 12 bytes
;nominal frequency: 16 MHz -> 10.6666666 cycles per bit, 85.333333333 cycles per byte
; Numbers in brackets are clocks counted from center of last sync bit
; when instruction starts
USB_INTR_VECTOR:
;order of registers pushed: YL, SREG YH, [sofError], bitcnt, shift, x1, x2, x3, x4, cnt
push YL ;[-25] push only what is necessary to sync with edge ASAP
in YL, SREG ;[-23]
push YL ;[-22]
push YH ;[-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 bitcnt ;[-12]
; [---] ;[-11]
lds YL, usbInputBufOffset;[-10]
; [---] ;[-9]
clr YH ;[-8]
subi YL, lo8(-(usbRxBuf));[-7] [rx loop init]
sbci YH, hi8(-(usbRxBuf));[-6] [rx loop init]
push shift ;[-5]
; [---] ;[-4]
ldi bitcnt, 0x55 ;[-3] [rx loop init]
sbis USBIN, USBMINUS ;[-2] we want two bits K (sample 2 cycles too early)
rjmp haveTwoBitsK ;[-1]
pop shift ;[0] undo the push from before
pop bitcnt ;[2] undo the push from before
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 (= 21 cycles).
;----------------------------------------------------------------------------
; push more registers and initialize values while we sample the first bits:
;----------------------------------------------------------------------------
haveTwoBitsK:
push x1 ;[1]
push x2 ;[3]
push x3 ;[5]
ldi shift, 0 ;[7]
ldi x3, 1<<4 ;[8] [rx loop init] first sample is inverse bit, compensate that
push x4 ;[9] == leap
in x1, USBIN ;[11] <-- sample bit 0
andi x1, USBMASK ;[12]
bst x1, USBMINUS ;[13]
bld shift, 7 ;[14]
push cnt ;[15]
ldi leap, 0 ;[17] [rx loop init]
ldi cnt, USB_BUFSIZE;[18] [rx loop init]
rjmp rxbit1 ;[19] arrives at [21]
;----------------------------------------------------------------------------
; Receiver loop (numbers in brackets are cycles within byte after instr)
;----------------------------------------------------------------------------
; duration of unstuffing code should be 10.66666667 cycles. We adjust "leap"
; accordingly to approximate this value in the long run.
unstuff6:
andi x2, USBMASK ;[03]
ori x3, 1<<6 ;[04] will not be shifted any more
andi shift, ~0x80;[05]
mov x1, x2 ;[06] sampled bit 7 is actually re-sampled bit 6
subi leap, -1 ;[07] total duration = 11 bits -> subtract 1/3
rjmp didUnstuff6 ;[08]
unstuff7:
ori x3, 1<<7 ;[09] will not be shifted any more
in x2, USBIN ;[00] [10] re-sample bit 7
andi x2, USBMASK ;[01]
andi shift, ~0x80;[02]
subi leap, 2 ;[03] total duration = 10 bits -> add 1/3
rjmp didUnstuff7 ;[04]
unstuffEven:
ori x3, 1<<6 ;[09] will be shifted right 6 times for bit 0
in x1, USBIN ;[00] [10]
andi shift, ~0x80;[01]
andi x1, USBMASK ;[02]
breq se0 ;[03]
subi leap, -1 ;[04] total duration = 11 bits -> subtract 1/3
nop2 ;[05]
rjmp didUnstuffE ;[06]
unstuffOdd:
ori x3, 1<<5 ;[09] will be shifted right 4 times for bit 1
in x2, USBIN ;[00] [10]
andi shift, ~0x80;[01]
andi x2, USBMASK ;[02]
breq se0 ;[03]
subi leap, -1 ;[04] total duration = 11 bits -> subtract 1/3
nop2 ;[05]
rjmp didUnstuffO ;[06]
rxByteLoop:
andi x1, USBMASK ;[03]
eor x2, x1 ;[04]
subi leap, 1 ;[05]
brpl skipLeap ;[06]
subi leap, -3 ;1 one leap cycle every 3rd byte -> 85 + 1/3 cycles per byte
nop ;1
skipLeap:
subi x2, 1 ;[08]
ror shift ;[09]
didUnstuff6:
cpi shift, 0xfc ;[10]
in x2, USBIN ;[00] [11] <-- sample bit 7
brcc unstuff6 ;[01]
andi x2, USBMASK ;[02]
eor x1, x2 ;[03]
subi x1, 1 ;[04]
ror shift ;[05]
didUnstuff7:
cpi shift, 0xfc ;[06]
brcc unstuff7 ;[07]
eor x3, shift ;[08] reconstruct: x3 is 1 at bit locations we changed, 0 at others
st y+, x3 ;[09] store data
rxBitLoop:
in x1, USBIN ;[00] [11] <-- sample bit 0/2/4
andi x1, USBMASK ;[01]
eor x2, x1 ;[02]
andi x3, 0x3f ;[03] topmost two bits reserved for 6 and 7
subi x2, 1 ;[04]
ror shift ;[05]
cpi shift, 0xfc ;[06]
brcc unstuffEven ;[07]
didUnstuffE:
lsr x3 ;[08]
lsr x3 ;[09]
rxbit1:
in x2, USBIN ;[00] [10] <-- sample bit 1/3/5
andi x2, USBMASK ;[01]
breq se0 ;[02]
eor x1, x2 ;[03]
subi x1, 1 ;[04]
ror shift ;[05]
cpi shift, 0xfc ;[06]
brcc unstuffOdd ;[07]
didUnstuffO:
subi bitcnt, 0xab;[08] == addi 0x55, 0x55 = 0x100/3
brcs rxBitLoop ;[09]
subi cnt, 1 ;[10]
in x1, USBIN ;[00] [11] <-- sample bit 6
brcc rxByteLoop ;[01]
rjmp overflow
macro POP_STANDARD ; 14 cycles
pop cnt
pop x4
pop x3
pop x2
pop x1
pop shift
pop bitcnt
endm
macro POP_RETI ; 7 cycles
pop YH
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
bitstuffN:
eor x1, x4 ;[5]
ldi x2, 0 ;[6]
nop2 ;[7]
nop ;[9]
out USBOUT, x1 ;[10] <-- out
rjmp didStuffN ;[0]
bitstuff6:
eor x1, x4 ;[5]
ldi x2, 0 ;[6] Carry is zero due to brcc
rol shift ;[7] compensate for ror shift at branch destination
rjmp didStuff6 ;[8]
bitstuff7:
ldi x2, 0 ;[2] Carry is zero due to brcc
rjmp didStuff7 ;[3]
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
;We don't match the transfer rate exactly (don't insert leap cycles every third
;byte) because the spec demands only 1.5% precision anyway.
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
txByteLoop:
ldi bitcnt, 0x35 ;[-4] [6] binary 0011 0101
txBitLoop:
sbrs shift, 0 ;[-3] [7]
eor x1, x4 ;[-2] [8]
out USBOUT, x1 ;[-1] [9] <-- out N
ror shift ;[0] [10]
ror x2 ;[1]
didStuffN:
cpi x2, 0xfc ;[2]
brcc bitstuffN ;[3]
lsr bitcnt ;[4]
brcc txBitLoop ;[5]
brne txBitLoop ;[6]
sbrs shift, 0 ;[7]
eor x1, x4 ;[8]
didStuff6:
out USBOUT, x1 ;[-1] [9] <-- out 6
ror shift ;[0] [10]
ror x2 ;[1]
cpi x2, 0xfc ;[2]
brcc bitstuff6 ;[3]
ror shift ;[4]
didStuff7:
ror x2 ;[5]
sbrs x2, 7 ;[6]
eor x1, x4 ;[7]
nop ;[8]
cpi x2, 0xfc ;[9]
out USBOUT, x1 ;[-1][10] <-- out 7
brcc bitstuff7 ;[0] [11]
ld shift, y+ ;[1]
dec cnt ;[3]
brne txByteLoop ;[4]
;make SE0:
cbr x1, USBMASK ;[5] prepare SE0 [spec says EOP may be 21 to 25 cycles]
lds x2, usbNewDeviceAddr;[6]
lsl x2 ;[8] we compare with left shifted address
subi YL, 20 + 2 ;[9] Only assign address on data packets, not ACK/NAK in x3
sbci YH, 0 ;[10]
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
breq skipAddrAssign ;[0]
sts usbDeviceAddr, x2; if not skipped: SE0 is one cycle longer
skipAddrAssign:
;end of usbDeviceAddress transfer
ldi x2, 1<<USB_INTR_PENDING_BIT;[2] int0 occurred during TX -- clear pending flag
USB_STORE_PENDING(x2) ;[3]
ori x1, USBIDLE ;[4]
in x2, USBDDR ;[5]
cbr x2, USBMASK ;[6] set both pins to input
mov x3, x1 ;[7]
cbr x3, USBMASK ;[8] configure no pullup on both pins
ldi x4, 4 ;[9]
se0Delay:
dec x4 ;[10] [13] [16] [19]
brne se0Delay ;[11] [14] [17] [20]
out USBOUT, x1 ;[21] <-- out J (idle) -- end of SE0 (EOP signal)
out USBDDR, x2 ;[22] <-- release bus now
out USBOUT, x3 ;[23] <-- ensure no pull-up resistors are active
rjmp doReturn
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