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359
usbdrv/usbdrvasm20.inc
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359
usbdrv/usbdrvasm20.inc
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/* Name: usbdrvasm20.inc
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* Project: V-USB, virtual USB port for Atmel's(r) AVR(r) microcontrollers
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* Author: Jeroen Benschop
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* Based on usbdrvasm16.inc from Christian Starkjohann
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* Creation Date: 2008-03-05
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* Tabsize: 4
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* Copyright: (c) 2008 by Jeroen Benschop and OBJECTIVE DEVELOPMENT Software GmbH
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* License: GNU GPL v2 (see License.txt), GNU GPL v3 or proprietary (CommercialLicense.txt)
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*/
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/* Do not link this file! Link usbdrvasm.S instead, which includes the
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* appropriate implementation!
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*/
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/*
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General Description:
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This file is the 20 MHz version of the asssembler part of the USB driver. It
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requires a 20 MHz crystal (not a ceramic resonator and not a calibrated RC
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oscillator).
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See usbdrv.h for a description of the entire driver.
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Since almost all of this code is timing critical, don't change unless you
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really know what you are doing! Many parts require not only a maximum number
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of CPU cycles, but even an exact number of cycles!
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*/
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#define leap2 x3
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#ifdef __IAR_SYSTEMS_ASM__
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#define nextInst $+2
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#else
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#define nextInst .+0
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#endif
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;max stack usage: [ret(2), YL, SREG, YH, bitcnt, shift, x1, x2, x3, x4, cnt] = 12 bytes
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;nominal frequency: 20 MHz -> 13.333333 cycles per bit, 106.666667 cycles per byte
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; Numbers in brackets are clocks counted from center of last sync bit
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; when instruction starts
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;register use in receive loop:
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; shift assembles the byte currently being received
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; x1 holds the D+ and D- line state
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; x2 holds the previous line state
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; x4 (leap) is used to add a leap cycle once every three bytes received
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; X3 (leap2) is used to add a leap cycle once every three stuff bits received
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; bitcnt is used to determine when a stuff bit is due
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; cnt holds the number of bytes left in the receive buffer
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USB_INTR_VECTOR:
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;order of registers pushed: YL, SREG YH, [sofError], bitcnt, shift, x1, x2, x3, x4, cnt
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push YL ;[-28] push only what is necessary to sync with edge ASAP
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in YL, SREG ;[-26]
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push YL ;[-25]
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push YH ;[-23]
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;----------------------------------------------------------------------------
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; Synchronize with sync pattern:
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;----------------------------------------------------------------------------
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;sync byte (D-) pattern LSb to MSb: 01010100 [1 = idle = J, 0 = K]
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;sync up with J to K edge during sync pattern -- use fastest possible loops
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;The first part waits at most 1 bit long since we must be in sync pattern.
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;YL is guarenteed to be < 0x80 because I flag is clear. When we jump to
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;waitForJ, ensure that this prerequisite is met.
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waitForJ:
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inc YL
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sbis USBIN, USBMINUS
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brne waitForJ ; just make sure we have ANY timeout
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waitForK:
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;The following code results in a sampling window of < 1/4 bit which meets the spec.
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sbis USBIN, USBMINUS ;[-19]
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rjmp foundK ;[-18]
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sbis USBIN, USBMINUS
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rjmp foundK
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sbis USBIN, USBMINUS
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rjmp foundK
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sbis USBIN, USBMINUS
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rjmp foundK
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sbis USBIN, USBMINUS
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rjmp foundK
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sbis USBIN, USBMINUS
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rjmp foundK
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sbis USBIN, USBMINUS
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rjmp foundK
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sbis USBIN, USBMINUS
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rjmp foundK
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sbis USBIN, USBMINUS
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rjmp foundK
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#if USB_COUNT_SOF
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lds YL, usbSofCount
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inc YL
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sts usbSofCount, YL
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#endif /* USB_COUNT_SOF */
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#ifdef USB_SOF_HOOK
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USB_SOF_HOOK
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#endif
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rjmp sofError
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foundK: ;[-16]
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;{3, 5} after falling D- edge, average delay: 4 cycles
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;bit0 should be at 34 for center sampling. Currently at 4 so 30 cylces till bit 0 sample
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;use 1 bit time for setup purposes, then sample again. Numbers in brackets
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;are cycles from center of first sync (double K) bit after the instruction
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push bitcnt ;[-16]
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; [---] ;[-15]
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lds YL, usbInputBufOffset;[-14]
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; [---] ;[-13]
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clr YH ;[-12]
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subi YL, lo8(-(usbRxBuf));[-11] [rx loop init]
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sbci YH, hi8(-(usbRxBuf));[-10] [rx loop init]
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push shift ;[-9]
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; [---] ;[-8]
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ldi shift,0x40 ;[-7] set msb to "1" so processing bit7 can be detected
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nop2 ;[-6]
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; [---] ;[-5]
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ldi bitcnt, 5 ;[-4] [rx loop init]
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sbis USBIN, USBMINUS ;[-3] we want two bits K (sample 3 cycles too early)
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rjmp haveTwoBitsK ;[-2]
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pop shift ;[-1] undo the push from before
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pop bitcnt ;[1]
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rjmp waitForK ;[3] this was not the end of sync, retry
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; The entire loop from waitForK until rjmp waitForK above must not exceed two
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; bit times (= 27 cycles).
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;----------------------------------------------------------------------------
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; push more registers and initialize values while we sample the first bits:
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;----------------------------------------------------------------------------
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haveTwoBitsK:
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push x1 ;[0]
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push x2 ;[2]
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push x3 ;[4] (leap2)
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ldi leap2, 0x55 ;[6] add leap cycle on 2nd,5th,8th,... stuff bit
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push x4 ;[7] == leap
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ldi leap, 0x55 ;[9] skip leap cycle on 2nd,5th,8th,... byte received
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push cnt ;[10]
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ldi cnt, USB_BUFSIZE ;[12] [rx loop init]
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ldi x2, 1<<USBPLUS ;[13] current line state is K state. D+=="1", D-=="0"
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bit0:
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in x1, USBIN ;[0] sample line state
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andi x1, USBMASK ;[1] filter only D+ and D- bits
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rjmp handleBit ;[2] make bit0 14 cycles long
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;----------------------------------------------------------------------------
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; Process bit7. However, bit 6 still may need unstuffing.
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;----------------------------------------------------------------------------
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b6checkUnstuff:
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dec bitcnt ;[9]
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breq unstuff6 ;[10]
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bit7:
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subi cnt, 1 ;[11] cannot use dec becaus it does not affect the carry flag
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brcs overflow ;[12] Too many bytes received. Ignore packet
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in x1, USBIN ;[0] sample line state
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andi x1, USBMASK ;[1] filter only D+ and D- bits
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cpse x1, x2 ;[2] when previous line state equals current line state, handle "1"
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rjmp b7handle0 ;[3] when line state differs, handle "0"
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sec ;[4]
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ror shift ;[5] shift "1" into the data
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st y+, shift ;[6] store the data into the buffer
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ldi shift, 0x40 ;[7] reset data for receiving the next byte
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subi leap, 0x55 ;[9] trick to introduce a leap cycle every 3 bytes
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brcc nextInst ;[10 or 11] it will fail after 85 bytes. However low speed can only receive 11
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dec bitcnt ;[11 or 12]
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brne bit0 ;[12 or 13]
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ldi x1, 1 ;[13 or 14] unstuffing bit 7
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in bitcnt, USBIN ;[0] sample stuff bit
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rjmp unstuff ;[1]
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b7handle0:
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mov x2,x1 ;[5] Set x2 to current line state
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ldi bitcnt, 6 ;[6]
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lsr shift ;[7] shift "0" into the data
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st y+, shift ;[8] store data into the buffer
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ldi shift, 0x40 ;[10] reset data for receiving the next byte
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subi leap, 0x55 ;[11] trick to introduce a leap cycle every 3 bytes
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brcs bit0 ;[12] it will fail after 85 bytes. However low speed can only receive 11
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rjmp bit0 ;[13]
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;----------------------------------------------------------------------------
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; Handle unstuff
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; x1==0xFF indicate unstuffing bit6
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;----------------------------------------------------------------------------
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unstuff6:
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ldi x1,0xFF ;[12] indicate unstuffing bit 6
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in bitcnt, USBIN ;[0] sample stuff bit
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nop ;[1] fix timing
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unstuff: ;b0-5 b6 b7
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mov x2,bitcnt ;[3] [2] [3] Set x2 to match line state
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subi leap2, 0x55 ;[4] [3] [4] delay loop
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brcs nextInst ;[5] [4] [5] add one cycle every three stuff bits
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sbci leap2,0 ;[6] [5] [6]
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ldi bitcnt,6 ;[7] [6] [7] reset bit stuff counter
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andi x2, USBMASK ;[8] [7] [8] only keep D+ and D-
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cpi x1,0 ;[9] [8] [9]
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brmi bit7 ;[10] [9] [10] finished unstuffing bit6 When x1<0
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breq bitloop ;[11] --- [11] finished unstuffing bit0-5 when x1=0
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nop ;--- --- [12]
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in x1, USBIN ;--- --- [0] sample line state for bit0
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andi x1, USBMASK ;--- --- [1] filter only D+ and D- bits
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rjmp handleBit ;--- --- [2] make bit0 14 cycles long
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;----------------------------------------------------------------------------
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; Receiver loop (numbers in brackets are cycles within byte after instr)
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;----------------------------------------------------------------------------
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bitloop:
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in x1, USBIN ;[0] sample line state
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andi x1, USBMASK ;[1] filter only D+ and D- bits
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breq se0 ;[2] both lines are low so handle se0
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handleBit:
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cpse x1, x2 ;[3] when previous line state equals current line state, handle "1"
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rjmp handle0 ;[4] when line state differs, handle "0"
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sec ;[5]
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ror shift ;[6] shift "1" into the data
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brcs b6checkUnstuff ;[7] When after shift C is set, next bit is bit7
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nop2 ;[8]
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dec bitcnt ;[10]
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brne bitloop ;[11]
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ldi x1,0 ;[12] indicate unstuff for bit other than bit6 or bit7
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in bitcnt, USBIN ;[0] sample stuff bit
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rjmp unstuff ;[1]
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handle0:
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mov x2, x1 ;[6] Set x2 to current line state
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ldi bitcnt, 6 ;[7] reset unstuff counter.
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lsr shift ;[8] shift "0" into the data
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brcs bit7 ;[9] When after shift C is set, next bit is bit7
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nop ;[10]
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rjmp bitloop ;[11]
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;----------------------------------------------------------------------------
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; End of receive loop. Now start handling EOP
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;----------------------------------------------------------------------------
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macro POP_STANDARD ; 14 cycles
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pop cnt
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pop x4
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pop x3
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pop x2
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pop x1
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pop shift
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pop bitcnt
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endm
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macro POP_RETI ; 7 cycles
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pop YH
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pop YL
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out SREG, YL
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pop YL
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endm
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#include "asmcommon.inc"
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; USB spec says:
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; idle = J
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; J = (D+ = 0), (D- = 1)
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; K = (D+ = 1), (D- = 0)
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; Spec allows 7.5 bit times from EOP to SOP for replies
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; 7.5 bit times is 100 cycles. This implementation arrives a bit later at se0
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; then specified in the include file but there is plenty of time
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bitstuffN:
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eor x1, x4 ;[8]
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ldi x2, 0 ;[9]
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nop2 ;[10]
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out USBOUT, x1 ;[12] <-- out
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rjmp didStuffN ;[0]
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bitstuff7:
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eor x1, x4 ;[6]
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ldi x2, 0 ;[7] Carry is zero due to brcc
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rol shift ;[8] compensate for ror shift at branch destination
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nop2 ;[9]
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rjmp didStuff7 ;[11]
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sendNakAndReti:
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ldi x3, USBPID_NAK ;[-18]
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rjmp sendX3AndReti ;[-17]
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sendAckAndReti:
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ldi cnt, USBPID_ACK ;[-17]
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sendCntAndReti:
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mov x3, cnt ;[-16]
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sendX3AndReti:
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ldi YL, 20 ;[-15] x3==r20 address is 20
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ldi YH, 0 ;[-14]
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ldi cnt, 2 ;[-13]
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; rjmp usbSendAndReti fallthrough
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;usbSend:
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;pointer to data in 'Y'
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;number of bytes in 'cnt' -- including sync byte [range 2 ... 12]
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;uses: x1...x4, btcnt, shift, cnt, Y
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;Numbers in brackets are time since first bit of sync pattern is sent
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;We don't match the transfer rate exactly (don't insert leap cycles every third
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;byte) because the spec demands only 1.5% precision anyway.
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usbSendAndReti: ; 12 cycles until SOP
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in x2, USBDDR ;[-12]
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ori x2, USBMASK ;[-11]
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sbi USBOUT, USBMINUS;[-10] prepare idle state; D+ and D- must have been 0 (no pullups)
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in x1, USBOUT ;[-8] port mirror for tx loop
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out USBDDR, x2 ;[-7] <- acquire bus
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; need not init x2 (bitstuff history) because sync starts with 0
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ldi x4, USBMASK ;[-6] exor mask
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ldi shift, 0x80 ;[-5] sync byte is first byte sent
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txByteLoop:
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ldi bitcnt, 0x49 ;[-4] [10] binary 01001001
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txBitLoop:
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sbrs shift, 0 ;[-3] [10] [11]
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eor x1, x4 ;[-2] [11] [12]
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out USBOUT, x1 ;[-1] [12] [13] <-- out N
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ror shift ;[0] [13] [14]
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ror x2 ;[1]
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didStuffN:
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nop2 ;[2]
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nop ;[4]
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cpi x2, 0xfc ;[5]
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brcc bitstuffN ;[6]
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lsr bitcnt ;[7]
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brcc txBitLoop ;[8]
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brne txBitLoop ;[9]
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sbrs shift, 0 ;[10]
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eor x1, x4 ;[11]
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didStuff7:
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out USBOUT, x1 ;[-1] [13] <-- out 7
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ror shift ;[0] [14]
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ror x2 ;[1]
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nop ;[2]
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cpi x2, 0xfc ;[3]
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brcc bitstuff7 ;[4]
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ld shift, y+ ;[5]
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dec cnt ;[7]
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brne txByteLoop ;[8]
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;make SE0:
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cbr x1, USBMASK ;[9] prepare SE0 [spec says EOP may be 25 to 30 cycles]
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lds x2, usbNewDeviceAddr;[10]
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lsl x2 ;[12] we compare with left shifted address
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out USBOUT, x1 ;[13] <-- out SE0 -- from now 2 bits = 22 cycles until bus idle
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subi YL, 20 + 2 ;[0] Only assign address on data packets, not ACK/NAK in x3
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sbci YH, 0 ;[1]
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;2006-03-06: moved transfer of new address to usbDeviceAddr from C-Code to asm:
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;set address only after data packet was sent, not after handshake
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breq skipAddrAssign ;[2]
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sts usbDeviceAddr, x2; if not skipped: SE0 is one cycle longer
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skipAddrAssign:
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;end of usbDeviceAddress transfer
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ldi x2, 1<<USB_INTR_PENDING_BIT;[4] int0 occurred during TX -- clear pending flag
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USB_STORE_PENDING(x2) ;[5]
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ori x1, USBIDLE ;[6]
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in x2, USBDDR ;[7]
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cbr x2, USBMASK ;[8] set both pins to input
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mov x3, x1 ;[9]
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cbr x3, USBMASK ;[10] configure no pullup on both pins
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ldi x4, 5 ;[11]
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se0Delay:
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dec x4 ;[12] [15] [18] [21] [24]
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brne se0Delay ;[13] [16] [19] [22] [25]
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out USBOUT, x1 ;[26] <-- out J (idle) -- end of SE0 (EOP signal)
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out USBDDR, x2 ;[27] <-- release bus now
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out USBOUT, x3 ;[28] <-- ensure no pull-up resistors are active
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rjmp doReturn
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