firmware/usbdrv/usbdrvasm20.inc

   1 /* Name: usbdrvasm20.inc
   2  * Project: V-USB, virtual USB port for Atmel's(r) AVR(r) microcontrollers
   3  * Author: Jeroen Benschop
   4  * Based on usbdrvasm16.inc from Christian Starkjohann
   5  * Creation Date: 2008-03-05
   6  * Tabsize: 4
   7  * Copyright: (c) 2008 by Jeroen Benschop and OBJECTIVE DEVELOPMENT Software GmbH
   8  * License: GNU GPL v2 (see License.txt), GNU GPL v3 or proprietary (CommercialLicense.txt)
   9  * Revision: $Id$
  10  */
  11
  12 /* Do not link this file! Link usbdrvasm.S instead, which includes the
  13  * appropriate implementation!
  14  */
  15
  16 /*
  17 General Description:
  18 This file is the 20 MHz version of the asssembler part of the USB driver. It
  19 requires a 20 MHz crystal (not a ceramic resonator and not a calibrated RC
  20 oscillator).
  21
  22 See usbdrv.h for a description of the entire driver.
  23
  24 Since almost all of this code is timing critical, don't change unless you
  25 really know what you are doing! Many parts require not only a maximum number
  26 of CPU cycles, but even an exact number of cycles!
  27 */
  28
  29 #define leap2   x3
  30 #ifdef __IAR_SYSTEMS_ASM__
  31 #define nextInst    $+2
  32 #else
  33 #define nextInst    .+0
  34 #endif
  35
  36 ;max stack usage: [ret(2), YL, SREG, YH, bitcnt, shift, x1, x2, x3, x4, cnt] = 12 bytes
  37 ;nominal frequency: 20 MHz -> 13.333333 cycles per bit, 106.666667 cycles per byte
  38 ; Numbers in brackets are clocks counted from center of last sync bit
  39 ; when instruction starts
  40 ;register use in receive loop:
  41 ; shift assembles the byte currently being received
  42 ; x1 holds the D+ and D- line state
  43 ; x2 holds the previous line state
  44 ; x4 (leap)  is used to add a leap cycle once every three bytes received
  45 ; X3 (leap2) is used to add a leap cycle once every three stuff bits received
  46 ; bitcnt is used to determine when a stuff bit is due
  47 ; cnt holds the number of bytes left in the receive buffer
  48
  49 USB_INTR_VECTOR:
  50 ;order of registers pushed: YL, SREG YH, [sofError], bitcnt, shift, x1, x2, x3, x4, cnt
  51     push    YL                  ;[-28] push only what is necessary to sync with edge ASAP
  52     in      YL, SREG            ;[-26]
  53     push    YL                  ;[-25]
  54     push    YH                  ;[-23]
  55 ;----------------------------------------------------------------------------
  56 ; Synchronize with sync pattern:
  57 ;----------------------------------------------------------------------------
  58 ;sync byte (D-) pattern LSb to MSb: 01010100 [1 = idle = J, 0 = K]
  59 ;sync up with J to K edge during sync pattern -- use fastest possible loops
  60 ;The first part waits at most 1 bit long since we must be in sync pattern.
  61 ;YL is guarenteed to be < 0x80 because I flag is clear. When we jump to
  62 ;waitForJ, ensure that this prerequisite is met.
  63 waitForJ:
  64     inc     YL
  65     sbis    USBIN, USBMINUS
  66     brne    waitForJ        ; just make sure we have ANY timeout
  67 waitForK:
  68 ;The following code results in a sampling window of < 1/4 bit which meets the spec.
  69     sbis    USBIN, USBMINUS     ;[-19]
  70     rjmp    foundK              ;[-18]
  71     sbis    USBIN, USBMINUS
  72     rjmp    foundK
  73     sbis    USBIN, USBMINUS
  74     rjmp    foundK
  75     sbis    USBIN, USBMINUS
  76     rjmp    foundK
  77     sbis    USBIN, USBMINUS
  78     rjmp    foundK
  79     sbis    USBIN, USBMINUS
  80     rjmp    foundK
  81     sbis    USBIN, USBMINUS
  82     rjmp    foundK
  83     sbis    USBIN, USBMINUS
  84     rjmp    foundK
  85     sbis    USBIN, USBMINUS
  86     rjmp    foundK
  87 #if USB_COUNT_SOF
  88     lds     YL, usbSofCount
  89     inc     YL
  90     sts     usbSofCount, YL
  91 #endif  /* USB_COUNT_SOF */
  92 #ifdef USB_SOF_HOOK
  93     USB_SOF_HOOK
  94 #endif
  95     rjmp    sofError
  96 foundK:                         ;[-16]
  97 ;{3, 5} after falling D- edge, average delay: 4 cycles
  98 ;bit0 should be at 34 for center sampling. Currently at 4 so 30 cylces till bit 0 sample
  99 ;use 1 bit time for setup purposes, then sample again. Numbers in brackets
 100 ;are cycles from center of first sync (double K) bit after the instruction
 101     push    bitcnt              ;[-16]
 102 ;   [---]                       ;[-15]
 103     lds     YL, usbInputBufOffset;[-14]
 104 ;   [---]                       ;[-13]
 105     clr     YH                  ;[-12]
 106     subi    YL, lo8(-(usbRxBuf));[-11] [rx loop init]
 107     sbci    YH, hi8(-(usbRxBuf));[-10] [rx loop init]
 108     push    shift               ;[-9]
 109 ;   [---]                       ;[-8]
 110     ldi     shift,0x40          ;[-7] set msb to "1" so processing bit7 can be detected
 111     nop2                        ;[-6]
 112 ;   [---]                       ;[-5]
 113     ldi     bitcnt, 5           ;[-4] [rx loop init]
 114     sbis    USBIN, USBMINUS     ;[-3] we want two bits K (sample 3 cycles too early)
 115     rjmp    haveTwoBitsK        ;[-2]
 116     pop     shift               ;[-1] undo the push from before
 117     pop     bitcnt              ;[1]
 118     rjmp    waitForK            ;[3] this was not the end of sync, retry
 119 ; The entire loop from waitForK until rjmp waitForK above must not exceed two
 120 ; bit times (= 27 cycles).
 121
 122 ;----------------------------------------------------------------------------
 123 ; push more registers and initialize values while we sample the first bits:
 124 ;----------------------------------------------------------------------------
 125 haveTwoBitsK:
 126     push    x1                  ;[0]
 127     push    x2                  ;[2]
 128     push    x3                  ;[4] (leap2)
 129     ldi     leap2, 0x55         ;[6] add leap cycle on 2nd,5th,8th,... stuff bit
 130     push    x4                  ;[7] == leap
 131     ldi     leap, 0x55          ;[9] skip leap cycle on 2nd,5th,8th,... byte received
 132     push    cnt                 ;[10]
 133     ldi     cnt, USB_BUFSIZE    ;[12] [rx loop init]
 134     ldi     x2, 1<<USBPLUS      ;[13] current line state is K state. D+=="1", D-=="0"
 135 bit0:
 136     in      x1, USBIN           ;[0] sample line state
 137     andi    x1, USBMASK         ;[1] filter only D+ and D- bits
 138     rjmp    handleBit           ;[2] make bit0 14 cycles long
 139
 140 ;----------------------------------------------------------------------------
 141 ; Process bit7. However, bit 6 still may need unstuffing.
 142 ;----------------------------------------------------------------------------
 143
 144 b6checkUnstuff:
 145     dec     bitcnt              ;[9]
 146     breq    unstuff6            ;[10]
 147 bit7:
 148     subi    cnt, 1              ;[11] cannot use dec becaus it does not affect the carry flag
 149     brcs    overflow            ;[12] Too many bytes received. Ignore packet
 150     in      x1, USBIN           ;[0] sample line state
 151     andi    x1, USBMASK         ;[1] filter only D+ and D- bits
 152     cpse    x1, x2              ;[2] when previous line state equals current line state, handle "1"
 153     rjmp    b7handle0           ;[3] when line state differs, handle "0"
 154     sec                         ;[4]
 155     ror     shift               ;[5] shift "1" into the data
 156     st      y+, shift           ;[6] store the data into the buffer
 157     ldi     shift, 0x40         ;[7] reset data for receiving the next byte
 158     subi    leap, 0x55          ;[9] trick to introduce a leap cycle every 3 bytes
 159     brcc    nextInst            ;[10 or 11] it will fail after 85 bytes. However low speed can only receive 11
 160     dec     bitcnt              ;[11 or 12]
 161     brne    bit0                ;[12 or 13]
 162     ldi     x1, 1               ;[13 or 14] unstuffing bit 7
 163     in      bitcnt, USBIN       ;[0] sample stuff bit
 164     rjmp    unstuff             ;[1]
 165
 166 b7handle0:
 167     mov     x2,x1               ;[5] Set x2 to current line state
 168     ldi     bitcnt, 6           ;[6]
 169     lsr     shift               ;[7] shift "0" into the data
 170     st      y+, shift           ;[8] store data into the buffer
 171     ldi     shift, 0x40         ;[10] reset data for receiving the next byte
 172     subi    leap, 0x55          ;[11] trick to introduce a leap cycle every 3 bytes
 173     brcs    bit0                ;[12] it will fail after 85 bytes. However low speed can only receive 11
 174     rjmp    bit0                ;[13]
 175
 176
 177 ;----------------------------------------------------------------------------
 178 ; Handle unstuff
 179 ; x1==0xFF indicate unstuffing bit6
 180 ;----------------------------------------------------------------------------
 181
 182 unstuff6:
 183     ldi     x1,0xFF             ;[12] indicate unstuffing bit 6
 184     in      bitcnt, USBIN       ;[0]  sample stuff bit
 185     nop                         ;[1]  fix timing
 186 unstuff:                        ;b0-5  b6   b7
 187     mov     x2,bitcnt           ;[3]  [2]  [3]  Set x2 to match line state
 188     subi    leap2, 0x55         ;[4]  [3]  [4]  delay loop
 189     brcs    nextInst            ;[5]  [4]  [5]  add one cycle every three stuff bits
 190     sbci    leap2,0             ;[6]  [5]  [6]
 191     ldi     bitcnt,6            ;[7]  [6]  [7]  reset bit stuff counter
 192     andi    x2, USBMASK         ;[8]  [7]  [8] only keep D+ and D-
 193     cpi     x1,0                ;[9]  [8]  [9]
 194     brmi    bit7                ;[10] [9]  [10] finished unstuffing bit6 When x1<0
 195     breq    bitloop             ;[11] ---  [11] finished unstuffing bit0-5 when x1=0
 196     nop                         ;---  ---  [12]
 197     in      x1, USBIN           ;---  ---  [0] sample line state for bit0
 198     andi    x1, USBMASK         ;---  ---  [1] filter only D+ and D- bits
 199     rjmp    handleBit           ;---  ---  [2] make bit0 14 cycles long
 200
 201 ;----------------------------------------------------------------------------
 202 ; Receiver loop (numbers in brackets are cycles within byte after instr)
 203 ;----------------------------------------------------------------------------
 204 bitloop:
 205     in      x1, USBIN           ;[0] sample line state
 206     andi    x1, USBMASK         ;[1] filter only D+ and D- bits
 207     breq    se0                 ;[2] both lines are low so handle se0
 208 handleBit:
 209     cpse    x1, x2              ;[3] when previous line state equals current line state, handle "1"
 210     rjmp    handle0             ;[4] when line state differs, handle "0"
 211     sec                         ;[5]
 212     ror     shift               ;[6] shift "1" into the data
 213     brcs    b6checkUnstuff      ;[7] When after shift C is set, next bit is bit7
 214     nop2                        ;[8]
 215     dec     bitcnt              ;[10]
 216     brne    bitloop             ;[11]
 217     ldi     x1,0                ;[12] indicate unstuff for bit other than bit6 or bit7
 218     in      bitcnt, USBIN       ;[0] sample stuff bit
 219     rjmp    unstuff             ;[1]
 220
 221 handle0:
 222     mov     x2, x1              ;[6] Set x2 to current line state
 223     ldi     bitcnt, 6           ;[7] reset unstuff counter.
 224     lsr     shift               ;[8] shift "0" into the data
 225     brcs    bit7                ;[9] When after shift C is set, next bit is bit7
 226     nop                         ;[10]
 227     rjmp    bitloop             ;[11]
 228
 229 ;----------------------------------------------------------------------------
 230 ; End of receive loop. Now start handling EOP
 231 ;----------------------------------------------------------------------------
 232
 233 macro POP_STANDARD ; 14 cycles
 234     pop     cnt
 235     pop     x4
 236     pop     x3
 237     pop     x2
 238     pop     x1
 239     pop     shift
 240     pop     bitcnt
 241     endm
 242 macro POP_RETI     ; 7 cycles
 243     pop     YH
 244     pop     YL
 245     out     SREG, YL
 246     pop     YL
 247     endm
 248
 249
 250
 251 #include "asmcommon.inc"
 252
 253 ; USB spec says:
 254 ; idle = J
 255 ; J = (D+ = 0), (D- = 1)
 256 ; K = (D+ = 1), (D- = 0)
 257 ; Spec allows 7.5 bit times from EOP to SOP for replies
 258 ; 7.5 bit times is 100 cycles. This implementation arrives a bit later at se0
 259 ; then specified in the include file but there is plenty of time
 260
 261 bitstuffN:
 262     eor     x1, x4          ;[8]
 263     ldi     x2, 0           ;[9]
 264     nop2                    ;[10]
 265     out     USBOUT, x1      ;[12] <-- out
 266     rjmp    didStuffN       ;[0]
 267
 268 bitstuff7:
 269     eor     x1, x4          ;[6]
 270     ldi     x2, 0           ;[7] Carry is zero due to brcc
 271     rol     shift           ;[8] compensate for ror shift at branch destination
 272     nop2                    ;[9]
 273     rjmp    didStuff7       ;[11]
 274
 275 sendNakAndReti:
 276     ldi     x3, USBPID_NAK  ;[-18]
 277     rjmp    sendX3AndReti   ;[-17]
 278 sendAckAndReti:
 279     ldi     cnt, USBPID_ACK ;[-17]
 280 sendCntAndReti:
 281     mov     x3, cnt         ;[-16]
 282 sendX3AndReti:
 283     ldi     YL, 20          ;[-15] x3==r20 address is 20
 284     ldi     YH, 0           ;[-14]
 285     ldi     cnt, 2          ;[-13]
 286 ;   rjmp    usbSendAndReti      fallthrough
 287
 288 ;usbSend:
 289 ;pointer to data in 'Y'
 290 ;number of bytes in 'cnt' -- including sync byte [range 2 ... 12]
 291 ;uses: x1...x4, btcnt, shift, cnt, Y
 292 ;Numbers in brackets are time since first bit of sync pattern is sent
 293 ;We don't match the transfer rate exactly (don't insert leap cycles every third
 294 ;byte) because the spec demands only 1.5% precision anyway.
 295 usbSendAndReti:             ; 12 cycles until SOP
 296     in      x2, USBDDR      ;[-12]
 297     ori     x2, USBMASK     ;[-11]
 298     sbi     USBOUT, USBMINUS;[-10] prepare idle state; D+ and D- must have been 0 (no pullups)
 299     in      x1, USBOUT      ;[-8] port mirror for tx loop
 300     out     USBDDR, x2      ;[-7] <- acquire bus
 301 ; need not init x2 (bitstuff history) because sync starts with 0
 302     ldi     x4, USBMASK     ;[-6] exor mask
 303     ldi     shift, 0x80     ;[-5] sync byte is first byte sent
 304 txByteLoop:
 305     ldi     bitcnt, 0x49    ;[-4]        [10] binary 01001001
 306 txBitLoop:
 307     sbrs    shift, 0        ;[-3] [10]   [11]
 308     eor     x1, x4          ;[-2] [11]   [12]
 309     out     USBOUT, x1      ;[-1] [12]   [13]   <-- out N
 310     ror     shift           ;[0]  [13]   [14]
 311     ror     x2              ;[1]
 312 didStuffN:
 313     nop2                    ;[2]
 314     nop                     ;[4]
 315     cpi     x2, 0xfc        ;[5]
 316     brcc    bitstuffN       ;[6]
 317     lsr     bitcnt          ;[7]
 318     brcc    txBitLoop       ;[8]
 319     brne    txBitLoop       ;[9]
 320
 321     sbrs    shift, 0        ;[10]
 322     eor     x1, x4          ;[11]
 323 didStuff7:
 324     out     USBOUT, x1      ;[-1] [13] <-- out 7
 325     ror     shift           ;[0] [14]
 326     ror     x2              ;[1]
 327     nop                     ;[2]
 328     cpi     x2, 0xfc        ;[3]
 329     brcc    bitstuff7       ;[4]
 330     ld      shift, y+       ;[5]
 331     dec     cnt             ;[7]
 332     brne    txByteLoop      ;[8]
 333 ;make SE0:
 334     cbr     x1, USBMASK     ;[9] prepare SE0 [spec says EOP may be 25 to 30 cycles]
 335     lds     x2, usbNewDeviceAddr;[10]
 336     lsl     x2              ;[12] we compare with left shifted address
 337     out     USBOUT, x1      ;[13] <-- out SE0 -- from now 2 bits = 22 cycles until bus idle
 338     subi    YL, 20 + 2      ;[0] Only assign address on data packets, not ACK/NAK in x3
 339     sbci    YH, 0           ;[1]
 340 ;2006-03-06: moved transfer of new address to usbDeviceAddr from C-Code to asm:
 341 ;set address only after data packet was sent, not after handshake
 342     breq    skipAddrAssign  ;[2]
 343     sts     usbDeviceAddr, x2; if not skipped: SE0 is one cycle longer
 344 skipAddrAssign:
 345 ;end of usbDeviceAddress transfer
 346     ldi     x2, 1<<USB_INTR_PENDING_BIT;[4] int0 occurred during TX -- clear pending flag
 347     USB_STORE_PENDING(x2)   ;[5]
 348     ori     x1, USBIDLE     ;[6]
 349     in      x2, USBDDR      ;[7]
 350     cbr     x2, USBMASK     ;[8] set both pins to input
 351     mov     x3, x1          ;[9]
 352     cbr     x3, USBMASK     ;[10] configure no pullup on both pins
 353     ldi     x4, 5           ;[11]
 354 se0Delay:
 355     dec     x4              ;[12] [15] [18] [21] [24]
 356     brne    se0Delay        ;[13] [16] [19] [22] [25]
 357     out     USBOUT, x1      ;[26] <-- out J (idle) -- end of SE0 (EOP signal)
 358     out     USBDDR, x2      ;[27] <-- release bus now
 359     out     USBOUT, x3      ;[28] <-- ensure no pull-up resistors are active
 360     rjmp    doReturn