mirror of
https://github.com/raphnet/dreamcast_usb
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707 lines
30 KiB
PHP
707 lines
30 KiB
PHP
/* Name: usbdrvasm18.inc
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* Project: V-USB, virtual USB port for Atmel's(r) AVR(r) microcontrollers
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* Author: Lukas Schrittwieser (based on 20 MHz usbdrvasm20.inc by Jeroen Benschop)
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* Creation Date: 2009-01-20
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* Tabsize: 4
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* Copyright: (c) 2008 by Lukas Schrittwieser 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 18 MHz version of the asssembler part of the USB driver. It
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requires a 18 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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;max stack usage: [ret(2), YL, SREG, YH, [sofError], bitcnt(x5), shift, x1, x2, x3, x4, cnt, ZL, ZH] = 14 bytes
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;nominal frequency: 18 MHz -> 12 cycles per bit
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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 to receive the data bytes:
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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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; cnt holds the number of bytes left in the receive buffer
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; x3 holds the higher crc byte (see algorithm below)
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; x4 is used as temporary register for the crc algorithm
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; x5 is used for unstuffing: when unstuffing the last received bit is inverted in shift (to prevent further
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; unstuffing calls. In the same time the corresponding bit in x5 is cleared to mark the bit as beening iverted
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; zl lower crc value and crc table index
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; zh used for crc table accesses
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;--------------------------------------------------------------------------------------------------------------
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; CRC mods:
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; table driven crc checker, Z points to table in prog space
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; ZL is the lower crc byte, x3 is the higher crc byte
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; x4 is used as temp register to store different results
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; the initialization of the crc register is not 0xFFFF but 0xFE54. This is because during the receipt of the
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; first data byte an virtual zero data byte is added to the crc register, this results in the correct initial
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; value of 0xFFFF at beginning of the second data byte before the first data byte is added to the crc.
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; The magic number 0xFE54 results form the crc table: At tabH[0x54] = 0xFF = crcH (required) and
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; tabL[0x54] = 0x01 -> crcL = 0x01 xor 0xFE = 0xFF
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; bitcnt is renamed to x5 and is used for unstuffing purposes, the unstuffing works like in the 12MHz version
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;--------------------------------------------------------------------------------------------------------------
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; CRC algorithm:
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; The crc register is formed by x3 (higher byte) and ZL (lower byte). The algorithm uses a 'reversed' form
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; i.e. that it takes the least significant bit first and shifts to the right. So in fact the highest order
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; bit seen from the polynomial devision point of view is the lsb of ZL. (If this sounds strange to you i
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; propose a research on CRC :-) )
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; Each data byte received is xored to ZL, the lower crc byte. This byte now builds the crc
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; table index. Next the new high byte is loaded from the table and stored in x4 until we have space in x3
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; (its destination).
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; Afterwards the lower table is loaded from the table and stored in ZL (the old index is overwritten as
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; we don't need it anymore. In fact this is a right shift by 8 bits.) Now the old crc high value is xored
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; to ZL, this is the second shift of the old crc value. Now x4 (the temp reg) is moved to x3 and the crc
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; calculation is done.
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; Prior to the first byte the two CRC register have to be initialized to 0xFFFF (as defined in usb spec)
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; however the crc engine also runs during the receipt of the first byte, therefore x3 and zl are initialized
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; to a magic number which results in a crc value of 0xFFFF after the first complete byte.
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;
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; This algorithm is split into the extra cycles of the different bits:
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; bit7: XOR the received byte to ZL
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; bit5: load the new high byte to x4
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; bit6: load the lower xor byte from the table, xor zl and x3, store result in zl (=the new crc low value)
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; move x4 (the new high byte) to x3, the crc value is ready
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;
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macro POP_STANDARD ; 18 cycles
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pop ZH
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pop ZL
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pop cnt
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pop x5
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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 x4
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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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macro CRC_CLEANUP_AND_CHECK
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; the last byte has already been xored with the lower crc byte, we have to do the table lookup and xor
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; x3 is the higher crc byte, zl the lower one
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ldi ZH, hi8(usbCrcTableHigh);[+1] get the new high byte from the table
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lpm x2, Z ;[+2][+3][+4]
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ldi ZH, hi8(usbCrcTableLow);[+5] get the new low xor byte from the table
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lpm ZL, Z ;[+6][+7][+8]
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eor ZL, x3 ;[+7] xor the old high byte with the value from the table, x2:ZL now holds the crc value
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cpi ZL, 0x01 ;[+8] if the crc is ok we have a fixed remainder value of 0xb001 in x2:ZL (see usb spec)
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brne ignorePacket ;[+9] detected a crc fault -> paket is ignored and retransmitted by the host
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cpi x2, 0xb0 ;[+10]
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brne ignorePacket ;[+11] detected a crc fault -> paket is ignored and retransmitted by the host
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endm
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USB_INTR_VECTOR:
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;order of registers pushed: YL, SREG, YH, [sofError], x4, shift, x1, x2, x3, x5, cnt, ZL, ZH
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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 ;[-17]
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rjmp foundK ;[-16]
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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: ;[-15]
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;{3, 5} after falling D- edge, average delay: 4 cycles
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;bit0 should be at 30 (2.5 bits) for center sampling. Currently at 4 so 26 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 x4 ;[-14]
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; [---] ;[-13]
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lds YL, usbInputBufOffset;[-12] used to toggle the two usb receive buffers
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; [---] ;[-11]
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clr YH ;[-10]
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subi YL, lo8(-(usbRxBuf));[-9] [rx loop init]
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sbci YH, hi8(-(usbRxBuf));[-8] [rx loop init]
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push shift ;[-7]
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; [---] ;[-6]
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ldi shift, 0x80 ;[-5] the last bit is the end of byte marker for the pid receiver loop
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clc ;[-4] the carry has to be clear for receipt of pid bit 0
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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 x4 ;[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 (= 24 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] crc high byte
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ldi x2, 1<<USBPLUS ;[6] [rx loop init] current line state is K state. D+=="1", D-=="0"
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push x5 ;[7]
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push cnt ;[9]
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ldi cnt, USB_BUFSIZE ;[11]
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;--------------------------------------------------------------------------------------------------------------
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; receives the pid byte
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; there is no real unstuffing algorithm implemented here as a stuffing bit is impossible in the pid byte.
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; That's because the last four bits of the byte are the inverted of the first four bits. If we detect a
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; unstuffing condition something went wrong and abort
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; shift has to be initialized to 0x80
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;--------------------------------------------------------------------------------------------------------------
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; pid bit 0 - used for even more register saving (we need the z pointer)
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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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eor x2, x1 ;[2] generate inverted of actual bit
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sbrc x2, USBMINUS ;[3] if the bit is set we received a zero
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sec ;[4]
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ror shift ;[5] we perform no unstuffing check here as this is the first bit
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mov x2, x1 ;[6]
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push ZL ;[7]
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;[8]
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push ZH ;[9]
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;[10]
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ldi x3, 0xFE ;[11] x3 is the high order crc value
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bitloopPid:
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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 nse0 ;[2] both lines are low so handle se0
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eor x2, x1 ;[3] generate inverted of actual bit
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sbrc x2, USBMINUS ;[4] set the carry if we received a zero
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sec ;[5]
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ror shift ;[6]
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ldi ZL, 0x54 ;[7] ZL is the low order crc value
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ser x4 ;[8] the is no bit stuffing check here as the pid bit can't be stuffed. if so
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; some error occured. In this case the paket is discarded later on anyway.
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mov x2, x1 ;[9] prepare for the next cycle
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brcc bitloopPid ;[10] while 0s drop out of shift we get the next bit
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eor x4, shift ;[11] invert all bits in shift and store result in x4
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;--------------------------------------------------------------------------------------------------------------
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; receives data bytes and calculates the crc
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; the last USBIN state has to be in x2
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; this is only the first half, due to branch distanc limitations the second half of the loop is near the end
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; of this asm file
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;--------------------------------------------------------------------------------------------------------------
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rxDataStart:
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in x1, USBIN ;[0] sample line state (note: a se0 check is not useful due to bit dribbling)
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ser x5 ;[1] prepare the unstuff marker register
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eor x2, x1 ;[2] generates the inverted of the actual bit
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bst x2, USBMINUS ;[3] copy the bit from x2
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bld shift, 0 ;[4] and store it in shift
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mov x2, shift ;[5] make a copy of shift for unstuffing check
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andi x2, 0xF9 ;[6] mask the last six bits, if we got six zeros (which are six ones in fact)
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breq unstuff0 ;[7] then Z is set now and we branch to the unstuffing handler
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didunstuff0:
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subi cnt, 1 ;[8] cannot use dec because it doesn't affect the carry flag
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brcs nOverflow ;[9] Too many bytes received. Ignore packet
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st Y+, x4 ;[10] store the last received byte
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;[11] st needs two cycles
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; bit1
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in x2, USBIN ;[0] sample line state
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andi x1, USBMASK ;[1] check for se0 during bit 0
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breq nse0 ;[2]
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andi x2, USBMASK ;[3] check se0 during bit 1
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breq nse0 ;[4]
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eor x1, x2 ;[5]
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bst x1, USBMINUS ;[6]
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bld shift, 1 ;[7]
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mov x1, shift ;[8]
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andi x1, 0xF3 ;[9]
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breq unstuff1 ;[10]
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didunstuff1:
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nop ;[11]
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; bit2
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in x1, USBIN ;[0] sample line state
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andi x1, USBMASK ;[1] check for se0 (as there is nothing else to do here
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breq nOverflow ;[2]
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eor x2, x1 ;[3] generates the inverted of the actual bit
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bst x2, USBMINUS ;[4]
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bld shift, 2 ;[5] store the bit
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mov x2, shift ;[6]
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andi x2, 0xE7 ;[7] if we have six zeros here (which means six 1 in the stream)
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breq unstuff2 ;[8] the next bit is a stuffing bit
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didunstuff2:
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nop2 ;[9]
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;[10]
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nop ;[11]
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; bit3
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in x2, USBIN ;[0] sample line state
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andi x2, USBMASK ;[1] check for se0
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breq nOverflow ;[2]
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eor x1, x2 ;[3]
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bst x1, USBMINUS ;[4]
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bld shift, 3 ;[5]
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mov x1, shift ;[6]
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andi x1, 0xCF ;[7]
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breq unstuff3 ;[8]
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didunstuff3:
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nop ;[9]
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rjmp rxDataBit4 ;[10]
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;[11]
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; the avr branch instructions allow an offset of +63 insturction only, so we need this
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; 'local copy' of se0
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nse0:
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rjmp se0 ;[4]
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;[5]
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; the same same as for se0 is needed for overflow and StuffErr
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nOverflow:
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stuffErr:
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rjmp overflow
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unstuff0: ;[8] this is the branch delay of breq unstuffX
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andi x1, USBMASK ;[9] do an se0 check here (if the last crc byte ends with 5 one's we might end up here
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breq didunstuff0 ;[10] event tough the message is complete -> jump back and store the byte
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ori shift, 0x01 ;[11] invert the last received bit to prevent furhter unstuffing
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in x2, USBIN ;[0] we have some free cycles so we could check for bit stuffing errors
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andi x5, 0xFE ;[1] mark this bit as inverted (will be corrected before storing shift)
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eor x1, x2 ;[2] x1 and x2 have to be different because the stuff bit is always a zero
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andi x1, USBMASK ;[3] mask the interesting bits
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breq stuffErr ;[4] if the stuff bit is a 1-bit something went wrong
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mov x1, x2 ;[5] the next bit expects the last state to be in x1
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rjmp didunstuff0 ;[6]
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;[7] jump delay of rjmp didunstuffX
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unstuff1: ;[11] this is the jump delay of breq unstuffX
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in x1, USBIN ;[0] we have some free cycles so we could check for bit stuffing errors
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ori shift, 0x02 ;[1] invert the last received bit to prevent furhter unstuffing
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andi x5, 0xFD ;[2] mark this bit as inverted (will be corrected before storing shift)
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eor x2, x1 ;[3] x1 and x2 have to be different because the stuff bit is always a zero
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andi x2, USBMASK ;[4] mask the interesting bits
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breq stuffErr ;[5] if the stuff bit is a 1-bit something went wrong
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mov x2, x1 ;[6] the next bit expects the last state to be in x2
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nop2 ;[7]
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;[8]
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rjmp didunstuff1 ;[9]
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;[10] jump delay of rjmp didunstuffX
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unstuff2: ;[9] this is the jump delay of breq unstuffX
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ori shift, 0x04 ;[10] invert the last received bit to prevent furhter unstuffing
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andi x5, 0xFB ;[11] mark this bit as inverted (will be corrected before storing shift)
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in x2, USBIN ;[0] we have some free cycles so we could check for bit stuffing errors
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eor x1, x2 ;[1] x1 and x2 have to be different because the stuff bit is always a zero
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andi x1, USBMASK ;[2] mask the interesting bits
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breq stuffErr ;[3] if the stuff bit is a 1-bit something went wrong
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mov x1, x2 ;[4] the next bit expects the last state to be in x1
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nop2 ;[5]
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;[6]
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rjmp didunstuff2 ;[7]
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;[8] jump delay of rjmp didunstuffX
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unstuff3: ;[9] this is the jump delay of breq unstuffX
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ori shift, 0x08 ;[10] invert the last received bit to prevent furhter unstuffing
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andi x5, 0xF7 ;[11] mark this bit as inverted (will be corrected before storing shift)
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in x1, USBIN ;[0] we have some free cycles so we could check for bit stuffing errors
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eor x2, x1 ;[1] x1 and x2 have to be different because the stuff bit is always a zero
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andi x2, USBMASK ;[2] mask the interesting bits
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breq stuffErr ;[3] if the stuff bit is a 1-bit something went wrong
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mov x2, x1 ;[4] the next bit expects the last state to be in x2
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nop2 ;[5]
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;[6]
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rjmp didunstuff3 ;[7]
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;[8] jump delay of rjmp didunstuffX
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; the include has to be here due to branch distance restirctions
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#define __USE_CRC__
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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 90 cycles. ...there is plenty of time
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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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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 ;[-6] <- acquire bus
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ldi x2, 0 ;[-6] init x2 (bitstuff history) because sync starts with 0
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ldi x4, USBMASK ;[-5] exor mask
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ldi shift, 0x80 ;[-4] sync byte is first byte sent
|
|
txByteLoop:
|
|
ldi bitcnt, 0x40 ;[-3]=[9] binary 01000000
|
|
txBitLoop: ; the loop sends the first 7 bits of the byte
|
|
sbrs shift, 0 ;[-2]=[10] if we have to send a 1 don't change the line state
|
|
eor x1, x4 ;[-1]=[11]
|
|
out USBOUT, x1 ;[0]
|
|
ror shift ;[1]
|
|
ror x2 ;[2] transfers the last sent bit to the stuffing history
|
|
didStuffN:
|
|
nop ;[3]
|
|
nop ;[4]
|
|
cpi x2, 0xfc ;[5] if we sent six consecutive ones
|
|
brcc bitstuffN ;[6]
|
|
lsr bitcnt ;[7]
|
|
brne txBitLoop ;[8] restart the loop while the 1 is still in the bitcount
|
|
|
|
; transmit bit 7
|
|
sbrs shift, 0 ;[9]
|
|
eor x1, x4 ;[10]
|
|
didStuff7:
|
|
ror shift ;[11]
|
|
out USBOUT, x1 ;[0] transfer bit 7 to the pins
|
|
ror x2 ;[1] move the bit into the stuffing history
|
|
cpi x2, 0xfc ;[2]
|
|
brcc bitstuff7 ;[3]
|
|
ld shift, y+ ;[4] get next byte to transmit
|
|
dec cnt ;[5] decrement byte counter
|
|
brne txByteLoop ;[7] if we have more bytes start next one
|
|
;[8] branch delay
|
|
|
|
;make SE0:
|
|
cbr x1, USBMASK ;[8] prepare SE0 [spec says EOP may be 25 to 30 cycles]
|
|
lds x2, usbNewDeviceAddr;[9]
|
|
lsl x2 ;[11] we compare with left shifted address
|
|
out USBOUT, x1 ;[0] <-- out SE0 -- from now 2 bits = 24 cycles until bus idle
|
|
subi YL, 20 + 2 ;[1] Only assign address on data packets, not ACK/NAK in x3
|
|
sbci YH, 0 ;[2]
|
|
;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 ;[3]
|
|
sts usbDeviceAddr, x2 ; if not skipped: SE0 is one cycle longer
|
|
skipAddrAssign:
|
|
;end of usbDeviceAddress transfer
|
|
ldi x2, 1<<USB_INTR_PENDING_BIT;[5] int0 occurred during TX -- clear pending flag
|
|
USB_STORE_PENDING(x2) ;[6]
|
|
ori x1, USBIDLE ;[7]
|
|
in x2, USBDDR ;[8]
|
|
cbr x2, USBMASK ;[9] set both pins to input
|
|
mov x3, x1 ;[10]
|
|
cbr x3, USBMASK ;[11] configure no pullup on both pins
|
|
ldi x4, 4 ;[12]
|
|
se0Delay:
|
|
dec x4 ;[13] [16] [19] [22]
|
|
brne se0Delay ;[14] [17] [20] [23]
|
|
out USBOUT, x1 ;[24] <-- out J (idle) -- end of SE0 (EOP signal)
|
|
out USBDDR, x2 ;[25] <-- release bus now
|
|
out USBOUT, x3 ;[26] <-- ensure no pull-up resistors are active
|
|
rjmp doReturn
|
|
|
|
bitstuffN:
|
|
eor x1, x4 ;[8] generate a zero
|
|
ldi x2, 0 ;[9] reset the bit stuffing history
|
|
nop2 ;[10]
|
|
out USBOUT, x1 ;[0] <-- send the stuffing bit
|
|
rjmp didStuffN ;[1]
|
|
|
|
bitstuff7:
|
|
eor x1, x4 ;[5]
|
|
ldi x2, 0 ;[6] reset bit stuffing history
|
|
clc ;[7] fill a zero into the shift register
|
|
rol shift ;[8] compensate for ror shift at branch destination
|
|
rjmp didStuff7 ;[9]
|
|
;[10] jump delay
|
|
|
|
;--------------------------------------------------------------------------------------------------------------
|
|
; receives data bytes and calculates the crc
|
|
; second half of the data byte receiver loop
|
|
; most parts of the crc algorithm are here
|
|
;--------------------------------------------------------------------------------------------------------------
|
|
|
|
nOverflow2:
|
|
rjmp overflow
|
|
|
|
rxDataBit4:
|
|
in x1, USBIN ;[0] sample line state
|
|
andi x1, USBMASK ;[1] check for se0
|
|
breq nOverflow2 ;[2]
|
|
eor x2, x1 ;[3]
|
|
bst x2, USBMINUS ;[4]
|
|
bld shift, 4 ;[5]
|
|
mov x2, shift ;[6]
|
|
andi x2, 0x9F ;[7]
|
|
breq unstuff4 ;[8]
|
|
didunstuff4:
|
|
nop2 ;[9][10]
|
|
nop ;[11]
|
|
|
|
; bit5
|
|
in x2, USBIN ;[0] sample line state
|
|
ldi ZH, hi8(usbCrcTableHigh);[1] use the table for the higher byte
|
|
eor x1, x2 ;[2]
|
|
bst x1, USBMINUS ;[3]
|
|
bld shift, 5 ;[4]
|
|
mov x1, shift ;[5]
|
|
andi x1, 0x3F ;[6]
|
|
breq unstuff5 ;[7]
|
|
didunstuff5:
|
|
lpm x4, Z ;[8] load the higher crc xor-byte and store it for later use
|
|
;[9] lpm needs 3 cycles
|
|
;[10]
|
|
ldi ZH, hi8(usbCrcTableLow);[11] load the lower crc xor byte adress
|
|
|
|
; bit6
|
|
in x1, USBIN ;[0] sample line state
|
|
eor x2, x1 ;[1]
|
|
bst x2, USBMINUS ;[2]
|
|
bld shift, 6 ;[3]
|
|
mov x2, shift ;[4]
|
|
andi x2, 0x7E ;[5]
|
|
breq unstuff6 ;[6]
|
|
didunstuff6:
|
|
lpm ZL, Z ;[7] load the lower xor crc byte
|
|
;[8] lpm needs 3 cycles
|
|
;[9]
|
|
eor ZL, x3 ;[10] xor the old high crc byte with the low xor-byte
|
|
mov x3, x4 ;[11] move the new high order crc value from temp to its destination
|
|
|
|
; bit7
|
|
in x2, USBIN ;[0] sample line state
|
|
eor x1, x2 ;[1]
|
|
bst x1, USBMINUS ;[2]
|
|
bld shift, 7 ;[3] now shift holds the complete but inverted data byte
|
|
mov x1, shift ;[4]
|
|
andi x1, 0xFC ;[5]
|
|
breq unstuff7 ;[6]
|
|
didunstuff7:
|
|
eor x5, shift ;[7] x5 marks all bits which have not been inverted by the unstuffing subs
|
|
mov x4, x5 ;[8] keep a copy of the data byte it will be stored during next bit0
|
|
eor ZL, x4 ;[9] feed the actual byte into the crc algorithm
|
|
rjmp rxDataStart ;[10] next byte
|
|
;[11] during the reception of the next byte this one will be fed int the crc algorithm
|
|
|
|
unstuff4: ;[9] this is the jump delay of rjmp unstuffX
|
|
ori shift, 0x10 ;[10] invert the last received bit to prevent furhter unstuffing
|
|
andi x5, 0xEF ;[11] mark this bit as inverted (will be corrected before storing shift)
|
|
in x2, USBIN ;[0] we have some free cycles so we could check for bit stuffing errors
|
|
eor x1, x2 ;[1] x1 and x2 have to be different because the stuff bit is always a zero
|
|
andi x1, USBMASK ;[2] mask the interesting bits
|
|
breq stuffErr2 ;[3] if the stuff bit is a 1-bit something went wrong
|
|
mov x1, x2 ;[4] the next bit expects the last state to be in x1
|
|
nop2 ;[5]
|
|
;[6]
|
|
rjmp didunstuff4 ;[7]
|
|
;[8] jump delay of rjmp didunstuffX
|
|
|
|
unstuff5: ;[8] this is the jump delay of rjmp unstuffX
|
|
nop ;[9]
|
|
ori shift, 0x20 ;[10] invert the last received bit to prevent furhter unstuffing
|
|
andi x5, 0xDF ;[11] mark this bit as inverted (will be corrected before storing shift)
|
|
in x1, USBIN ;[0] we have some free cycles so we could check for bit stuffing errors
|
|
eor x2, x1 ;[1] x1 and x2 have to be different because the stuff bit is always a zero
|
|
andi x2, USBMASK ;[2] mask the interesting bits
|
|
breq stuffErr2 ;[3] if the stuff bit is a 1-bit something went wrong
|
|
mov x2, x1 ;[4] the next bit expects the last state to be in x2
|
|
nop ;[5]
|
|
rjmp didunstuff5 ;[6]
|
|
;[7] jump delay of rjmp didunstuffX
|
|
|
|
unstuff6: ;[7] this is the jump delay of rjmp unstuffX
|
|
nop2 ;[8]
|
|
;[9]
|
|
ori shift, 0x40 ;[10] invert the last received bit to prevent furhter unstuffing
|
|
andi x5, 0xBF ;[11] mark this bit as inverted (will be corrected before storing shift)
|
|
in x2, USBIN ;[0] we have some free cycles so we could check for bit stuffing errors
|
|
eor x1, x2 ;[1] x1 and x2 have to be different because the stuff bit is always a zero
|
|
andi x1, USBMASK ;[2] mask the interesting bits
|
|
breq stuffErr2 ;[3] if the stuff bit is a 1-bit something went wrong
|
|
mov x1, x2 ;[4] the next bit expects the last state to be in x1
|
|
rjmp didunstuff6 ;[5]
|
|
;[6] jump delay of rjmp didunstuffX
|
|
|
|
unstuff7: ;[7] this is the jump delay of rjmp unstuffX
|
|
nop ;[8]
|
|
nop ;[9]
|
|
ori shift, 0x80 ;[10] invert the last received bit to prevent furhter unstuffing
|
|
andi x5, 0x7F ;[11] mark this bit as inverted (will be corrected before storing shift)
|
|
in x1, USBIN ;[0] we have some free cycles so we could check for bit stuffing errors
|
|
eor x2, x1 ;[1] x1 and x2 have to be different because the stuff bit is always a zero
|
|
andi x2, USBMASK ;[2] mask the interesting bits
|
|
breq stuffErr2 ;[3] if the stuff bit is a 1-bit something went wrong
|
|
mov x2, x1 ;[4] the next bit expects the last state to be in x2
|
|
rjmp didunstuff7 ;[5]
|
|
;[6] jump delay of rjmp didunstuff7
|
|
|
|
; local copy of the stuffErr desitnation for the second half of the receiver loop
|
|
stuffErr2:
|
|
rjmp stuffErr
|
|
|
|
;--------------------------------------------------------------------------------------------------------------
|
|
; The crc table follows. It has to be aligned to enable a fast loading of the needed bytes.
|
|
; There are two tables of 256 entries each, the low and the high byte table.
|
|
; Table values were generated with the following C code:
|
|
/*
|
|
#include <stdio.h>
|
|
int main (int argc, char **argv)
|
|
{
|
|
int i, j;
|
|
for (i=0; i<512; i++){
|
|
unsigned short crc = i & 0xff;
|
|
for(j=0; j<8; j++) crc = (crc >> 1) ^ ((crc & 1) ? 0xa001 : 0);
|
|
if((i & 7) == 0) printf("\n.byte ");
|
|
printf("0x%02x, ", (i > 0xff ? (crc >> 8) : crc) & 0xff);
|
|
if(i == 255) printf("\n");
|
|
}
|
|
return 0;
|
|
}
|
|
|
|
// Use the following algorithm to compute CRC values:
|
|
ushort computeCrc(uchar *msg, uchar msgLen)
|
|
{
|
|
uchar i;
|
|
ushort crc = 0xffff;
|
|
for(i = 0; i < msgLen; i++)
|
|
crc = usbCrcTable16[lo8(crc) ^ msg[i]] ^ hi8(crc);
|
|
return crc;
|
|
}
|
|
*/
|
|
|
|
.balign 256
|
|
usbCrcTableLow:
|
|
.byte 0x00, 0xC1, 0x81, 0x40, 0x01, 0xC0, 0x80, 0x41
|
|
.byte 0x01, 0xC0, 0x80, 0x41, 0x00, 0xC1, 0x81, 0x40
|
|
.byte 0x01, 0xC0, 0x80, 0x41, 0x00, 0xC1, 0x81, 0x40
|
|
.byte 0x00, 0xC1, 0x81, 0x40, 0x01, 0xC0, 0x80, 0x41
|
|
.byte 0x01, 0xC0, 0x80, 0x41, 0x00, 0xC1, 0x81, 0x40
|
|
.byte 0x00, 0xC1, 0x81, 0x40, 0x01, 0xC0, 0x80, 0x41
|
|
.byte 0x00, 0xC1, 0x81, 0x40, 0x01, 0xC0, 0x80, 0x41
|
|
.byte 0x01, 0xC0, 0x80, 0x41, 0x00, 0xC1, 0x81, 0x40
|
|
.byte 0x01, 0xC0, 0x80, 0x41, 0x00, 0xC1, 0x81, 0x40
|
|
.byte 0x00, 0xC1, 0x81, 0x40, 0x01, 0xC0, 0x80, 0x41
|
|
.byte 0x00, 0xC1, 0x81, 0x40, 0x01, 0xC0, 0x80, 0x41
|
|
.byte 0x01, 0xC0, 0x80, 0x41, 0x00, 0xC1, 0x81, 0x40
|
|
.byte 0x00, 0xC1, 0x81, 0x40, 0x01, 0xC0, 0x80, 0x41
|
|
.byte 0x01, 0xC0, 0x80, 0x41, 0x00, 0xC1, 0x81, 0x40
|
|
.byte 0x01, 0xC0, 0x80, 0x41, 0x00, 0xC1, 0x81, 0x40
|
|
.byte 0x00, 0xC1, 0x81, 0x40, 0x01, 0xC0, 0x80, 0x41
|
|
.byte 0x01, 0xC0, 0x80, 0x41, 0x00, 0xC1, 0x81, 0x40
|
|
.byte 0x00, 0xC1, 0x81, 0x40, 0x01, 0xC0, 0x80, 0x41
|
|
.byte 0x00, 0xC1, 0x81, 0x40, 0x01, 0xC0, 0x80, 0x41
|
|
.byte 0x01, 0xC0, 0x80, 0x41, 0x00, 0xC1, 0x81, 0x40
|
|
.byte 0x00, 0xC1, 0x81, 0x40, 0x01, 0xC0, 0x80, 0x41
|
|
.byte 0x01, 0xC0, 0x80, 0x41, 0x00, 0xC1, 0x81, 0x40
|
|
.byte 0x01, 0xC0, 0x80, 0x41, 0x00, 0xC1, 0x81, 0x40
|
|
.byte 0x00, 0xC1, 0x81, 0x40, 0x01, 0xC0, 0x80, 0x41
|
|
.byte 0x00, 0xC1, 0x81, 0x40, 0x01, 0xC0, 0x80, 0x41
|
|
.byte 0x01, 0xC0, 0x80, 0x41, 0x00, 0xC1, 0x81, 0x40
|
|
.byte 0x01, 0xC0, 0x80, 0x41, 0x00, 0xC1, 0x81, 0x40
|
|
.byte 0x00, 0xC1, 0x81, 0x40, 0x01, 0xC0, 0x80, 0x41
|
|
.byte 0x01, 0xC0, 0x80, 0x41, 0x00, 0xC1, 0x81, 0x40
|
|
.byte 0x00, 0xC1, 0x81, 0x40, 0x01, 0xC0, 0x80, 0x41
|
|
.byte 0x00, 0xC1, 0x81, 0x40, 0x01, 0xC0, 0x80, 0x41
|
|
.byte 0x01, 0xC0, 0x80, 0x41, 0x00, 0xC1, 0x81, 0x40
|
|
|
|
; .balign 256
|
|
usbCrcTableHigh:
|
|
.byte 0x00, 0xC0, 0xC1, 0x01, 0xC3, 0x03, 0x02, 0xC2
|
|
.byte 0xC6, 0x06, 0x07, 0xC7, 0x05, 0xC5, 0xC4, 0x04
|
|
.byte 0xCC, 0x0C, 0x0D, 0xCD, 0x0F, 0xCF, 0xCE, 0x0E
|
|
.byte 0x0A, 0xCA, 0xCB, 0x0B, 0xC9, 0x09, 0x08, 0xC8
|
|
.byte 0xD8, 0x18, 0x19, 0xD9, 0x1B, 0xDB, 0xDA, 0x1A
|
|
.byte 0x1E, 0xDE, 0xDF, 0x1F, 0xDD, 0x1D, 0x1C, 0xDC
|
|
.byte 0x14, 0xD4, 0xD5, 0x15, 0xD7, 0x17, 0x16, 0xD6
|
|
.byte 0xD2, 0x12, 0x13, 0xD3, 0x11, 0xD1, 0xD0, 0x10
|
|
.byte 0xF0, 0x30, 0x31, 0xF1, 0x33, 0xF3, 0xF2, 0x32
|
|
.byte 0x36, 0xF6, 0xF7, 0x37, 0xF5, 0x35, 0x34, 0xF4
|
|
.byte 0x3C, 0xFC, 0xFD, 0x3D, 0xFF, 0x3F, 0x3E, 0xFE
|
|
.byte 0xFA, 0x3A, 0x3B, 0xFB, 0x39, 0xF9, 0xF8, 0x38
|
|
.byte 0x28, 0xE8, 0xE9, 0x29, 0xEB, 0x2B, 0x2A, 0xEA
|
|
.byte 0xEE, 0x2E, 0x2F, 0xEF, 0x2D, 0xED, 0xEC, 0x2C
|
|
.byte 0xE4, 0x24, 0x25, 0xE5, 0x27, 0xE7, 0xE6, 0x26
|
|
.byte 0x22, 0xE2, 0xE3, 0x23, 0xE1, 0x21, 0x20, 0xE0
|
|
.byte 0xA0, 0x60, 0x61, 0xA1, 0x63, 0xA3, 0xA2, 0x62
|
|
.byte 0x66, 0xA6, 0xA7, 0x67, 0xA5, 0x65, 0x64, 0xA4
|
|
.byte 0x6C, 0xAC, 0xAD, 0x6D, 0xAF, 0x6F, 0x6E, 0xAE
|
|
.byte 0xAA, 0x6A, 0x6B, 0xAB, 0x69, 0xA9, 0xA8, 0x68
|
|
.byte 0x78, 0xB8, 0xB9, 0x79, 0xBB, 0x7B, 0x7A, 0xBA
|
|
.byte 0xBE, 0x7E, 0x7F, 0xBF, 0x7D, 0xBD, 0xBC, 0x7C
|
|
.byte 0xB4, 0x74, 0x75, 0xB5, 0x77, 0xB7, 0xB6, 0x76
|
|
.byte 0x72, 0xB2, 0xB3, 0x73, 0xB1, 0x71, 0x70, 0xB0
|
|
.byte 0x50, 0x90, 0x91, 0x51, 0x93, 0x53, 0x52, 0x92
|
|
.byte 0x96, 0x56, 0x57, 0x97, 0x55, 0x95, 0x94, 0x54
|
|
.byte 0x9C, 0x5C, 0x5D, 0x9D, 0x5F, 0x9F, 0x9E, 0x5E
|
|
.byte 0x5A, 0x9A, 0x9B, 0x5B, 0x99, 0x59, 0x58, 0x98
|
|
.byte 0x88, 0x48, 0x49, 0x89, 0x4B, 0x8B, 0x8A, 0x4A
|
|
.byte 0x4E, 0x8E, 0x8F, 0x4F, 0x8D, 0x4D, 0x4C, 0x8C
|
|
.byte 0x44, 0x84, 0x85, 0x45, 0x87, 0x47, 0x46, 0x86
|
|
.byte 0x82, 0x42, 0x43, 0x83, 0x41, 0x81, 0x80, 0x40
|
|
|