usbdrv/usbdrvasm16.inc@99a5439f349f
usbdrv/usbdrvasm16.inc
Thu, 16 Feb 2017 16:24:25 +0100
- author
- Malte Di Donato <mdd@neo-soft.org>
- date
- Thu, 16 Feb 2017 16:24:25 +0100
- changeset 4
- 99a5439f349f
- parent 0
- 9e9b2c78bd31
- permissions
- -rw-r--r--
calibration tests added
/* 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) */ /* 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
