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4nes4snes/usbdrv/usbdrvasm12.S

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/* Name: usbdrvasm12.S
* Project: AVR USB driver
* Author: Christian Starkjohann
* Creation Date: 2004-12-29
* Tabsize: 4
* Copyright: (c) 2007 by OBJECTIVE DEVELOPMENT Software GmbH
* License: GNU GPL v2 (see License.txt) or proprietary (CommercialLicense.txt)
* This Revision: $Id: usbdrvasm12.S,v 1.1 2013-04-25 02:18:15 cvs Exp $
*/
/* Do not link this file! Link usbdrvasm.S instead, which includes the
* appropriate implementation!
*/
/*
General Description:
This file is the 12 MHz version of the asssembler part of the USB driver. It
requires a 12 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!
Timing constraints according to spec (in bit times):
timing subject min max CPUcycles
---------------------------------------------------------------------------
EOP of OUT/SETUP to sync pattern of DATA0 (both rx) 2 16 16-128
EOP of IN to sync pattern of DATA0 (rx, then tx) 2 7.5 16-60
DATAx (rx) to ACK/NAK/STALL (tx) 2 7.5 16-60
*/
;Software-receiver engine. Strict timing! Don't change unless you can preserve timing!
;interrupt response time: 4 cycles + insn running = 7 max if interrupts always enabled
;max allowable interrupt latency: 34 cycles -> max 25 cycles interrupt disable
;max stack usage: [ret(2), YL, SREG, YH, shift, x1, x2, x3, cnt, x4] = 11 bytes
;Numbers in brackets are maximum cycles since SOF.
USB_INTR_VECTOR:
;order of registers pushed: YL, SREG [sofError], YH, shift, x1, x2, x3, cnt
push YL ;2 [35] push only what is necessary to sync with edge ASAP
in YL, SREG ;1 [37]
push YL ;2 [39]
;----------------------------------------------------------------------------
; 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
;first part has no timeout because it waits for IDLE or SE1 (== disconnected)
waitForJ:
sbis USBIN, USBMINUS ;1 [40] wait for D- == 1
rjmp waitForJ ;2
waitForK:
;The following code results in a sampling window of 1/4 bit which meets the spec.
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 */
rjmp sofError
foundK:
;{3, 5} after falling D- edge, average delay: 4 cycles [we want 4 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 YH ;2 [2]
lds YL, usbInputBufOffset;2 [4]
clr YH ;1 [5]
subi YL, lo8(-(usbRxBuf));1 [6]
sbci YH, hi8(-(usbRxBuf));1 [7]
sbis USBIN, USBMINUS ;1 [8] we want two bits K [sample 1 cycle too early]
rjmp haveTwoBitsK ;2 [10]
pop YH ;2 [11] undo the push from before
rjmp waitForK ;2 [13] this was not the end of sync, retry
haveTwoBitsK:
;----------------------------------------------------------------------------
; push more registers and initialize values while we sample the first bits:
;----------------------------------------------------------------------------
push shift ;2 [16]
push x1 ;2 [12]
push x2 ;2 [14]
in x1, USBIN ;1 [17] <-- sample bit 0
ldi shift, 0xff ;1 [18]
bst x1, USBMINUS ;1 [19]
bld shift, 0 ;1 [20]
push x3 ;2 [22]
push cnt ;2 [24]
in x2, USBIN ;1 [25] <-- sample bit 1
ser x3 ;1 [26] [inserted init instruction]
eor x1, x2 ;1 [27]
bst x1, USBMINUS ;1 [28]
bld shift, 1 ;1 [29]
ldi cnt, USB_BUFSIZE;1 [30] [inserted init instruction]
rjmp rxbit2 ;2 [32]
;----------------------------------------------------------------------------
; Receiver loop (numbers in brackets are cycles within byte after instr)
;----------------------------------------------------------------------------
unstuff0: ;1 (branch taken)
andi x3, ~0x01 ;1 [15]
mov x1, x2 ;1 [16] x2 contains last sampled (stuffed) bit
in x2, USBIN ;1 [17] <-- sample bit 1 again
ori shift, 0x01 ;1 [18]
rjmp didUnstuff0 ;2 [20]
unstuff1: ;1 (branch taken)
mov x2, x1 ;1 [21] x1 contains last sampled (stuffed) bit
andi x3, ~0x02 ;1 [22]
ori shift, 0x02 ;1 [23]
nop ;1 [24]
in x1, USBIN ;1 [25] <-- sample bit 2 again
rjmp didUnstuff1 ;2 [27]
unstuff2: ;1 (branch taken)
andi x3, ~0x04 ;1 [29]
ori shift, 0x04 ;1 [30]
mov x1, x2 ;1 [31] x2 contains last sampled (stuffed) bit
nop ;1 [32]
in x2, USBIN ;1 [33] <-- sample bit 3
rjmp didUnstuff2 ;2 [35]
unstuff3: ;1 (branch taken)
in x2, USBIN ;1 [34] <-- sample stuffed bit 3 [one cycle too late]
andi x3, ~0x08 ;1 [35]
ori shift, 0x08 ;1 [36]
rjmp didUnstuff3 ;2 [38]
unstuff4: ;1 (branch taken)
andi x3, ~0x10 ;1 [40]
in x1, USBIN ;1 [41] <-- sample stuffed bit 4
ori shift, 0x10 ;1 [42]
rjmp didUnstuff4 ;2 [44]
unstuff5: ;1 (branch taken)
andi x3, ~0x20 ;1 [48]
in x2, USBIN ;1 [49] <-- sample stuffed bit 5
ori shift, 0x20 ;1 [50]
rjmp didUnstuff5 ;2 [52]
unstuff6: ;1 (branch taken)
andi x3, ~0x40 ;1 [56]
in x1, USBIN ;1 [57] <-- sample stuffed bit 6
ori shift, 0x40 ;1 [58]
rjmp didUnstuff6 ;2 [60]
; extra jobs done during bit interval:
; bit 0: store, clear [SE0 is unreliable here due to bit dribbling in hubs]
; bit 1: se0 check
; bit 2: overflow check
; bit 3: recovery from delay [bit 0 tasks took too long]
; bit 4: none
; bit 5: none
; bit 6: none
; bit 7: jump, eor
rxLoop:
eor x3, shift ;1 [0] reconstruct: x3 is 0 at bit locations we changed, 1 at others
in x1, USBIN ;1 [1] <-- sample bit 0
st y+, x3 ;2 [3] store data
ser x3 ;1 [4]
nop ;1 [5]
eor x2, x1 ;1 [6]
bst x2, USBMINUS;1 [7]
bld shift, 0 ;1 [8]
in x2, USBIN ;1 [9] <-- sample bit 1 (or possibly bit 0 stuffed)
andi x2, USBMASK ;1 [10]
breq se0 ;1 [11] SE0 check for bit 1
andi shift, 0xf9 ;1 [12]
didUnstuff0:
breq unstuff0 ;1 [13]
eor x1, x2 ;1 [14]
bst x1, USBMINUS;1 [15]
bld shift, 1 ;1 [16]
rxbit2:
in x1, USBIN ;1 [17] <-- sample bit 2 (or possibly bit 1 stuffed)
andi shift, 0xf3 ;1 [18]
breq unstuff1 ;1 [19] do remaining work for bit 1
didUnstuff1:
subi cnt, 1 ;1 [20]
brcs overflow ;1 [21] loop control
eor x2, x1 ;1 [22]
bst x2, USBMINUS;1 [23]
bld shift, 2 ;1 [24]
in x2, USBIN ;1 [25] <-- sample bit 3 (or possibly bit 2 stuffed)
andi shift, 0xe7 ;1 [26]
breq unstuff2 ;1 [27]
didUnstuff2:
eor x1, x2 ;1 [28]
bst x1, USBMINUS;1 [29]
bld shift, 3 ;1 [30]
didUnstuff3:
andi shift, 0xcf ;1 [31]
breq unstuff3 ;1 [32]
in x1, USBIN ;1 [33] <-- sample bit 4
eor x2, x1 ;1 [34]
bst x2, USBMINUS;1 [35]
bld shift, 4 ;1 [36]
didUnstuff4:
andi shift, 0x9f ;1 [37]
breq unstuff4 ;1 [38]
nop2 ;2 [40]
in x2, USBIN ;1 [41] <-- sample bit 5
eor x1, x2 ;1 [42]
bst x1, USBMINUS;1 [43]
bld shift, 5 ;1 [44]
didUnstuff5:
andi shift, 0x3f ;1 [45]
breq unstuff5 ;1 [46]
nop2 ;2 [48]
in x1, USBIN ;1 [49] <-- sample bit 6
eor x2, x1 ;1 [50]
bst x2, USBMINUS;1 [51]
bld shift, 6 ;1 [52]
didUnstuff6:
cpi shift, 0x02 ;1 [53]
brlo unstuff6 ;1 [54]
nop2 ;2 [56]
in x2, USBIN ;1 [57] <-- sample bit 7
eor x1, x2 ;1 [58]
bst x1, USBMINUS;1 [59]
bld shift, 7 ;1 [60]
didUnstuff7:
cpi shift, 0x04 ;1 [61]
brsh rxLoop ;2 [63] loop control
unstuff7:
andi x3, ~0x80 ;1 [63]
ori shift, 0x80 ;1 [64]
in x2, USBIN ;1 [65] <-- sample stuffed bit 7
nop ;1 [66]
rjmp didUnstuff7 ;2 [68]
;----------------------------------------------------------------------------
; Processing of received packet (numbers in brackets are cycles after end of SE0)
;----------------------------------------------------------------------------
;This is the only non-error exit point for the software receiver loop
;we don't check any CRCs here because there is no time left.
#define token x1
se0: ; [0]
subi cnt, USB_BUFSIZE ;1 [1]
neg cnt ;1 [2]
cpi cnt, 3 ;1 [3]
ldi x2, 1<<USB_INTR_PENDING_BIT ;1 [4]
USB_STORE_PENDING(x2) ;1 [5] clear pending intr and check flag later. SE0 should be over.
brlo doReturn ;1 [6] this is probably an ACK, NAK or similar packet
sub YL, cnt ;1 [7]
sbci YH, 0 ;1 [8]
ld token, y ;2 [10]
cpi token, USBPID_DATA0 ;1 [11]
breq handleData ;1 [12]
cpi token, USBPID_DATA1 ;1 [13]
breq handleData ;1 [14]
ldd x2, y+1 ;2 [16] ADDR and 1 bit endpoint number
mov x3, x2 ;1 [17] store for endpoint number
andi x2, 0x7f ;1 [18] x2 is now ADDR
lds shift, usbDeviceAddr;2 [20]
cp x2, shift ;1 [21]
overflow: ; This is a hack: brcs overflow will never have Z flag set
brne ignorePacket ;1 [22] packet for different address
cpi token, USBPID_IN ;1 [23]
breq handleIn ;1 [24]
cpi token, USBPID_SETUP ;1 [25]
breq handleSetupOrOut ;1 [26]
cpi token, USBPID_OUT ;1 [27]
breq handleSetupOrOut ;1 [28]
; rjmp ignorePacket ;fallthrough, should not happen anyway.
ignorePacket:
clr shift
sts usbCurrentTok, shift
doReturn:
pop cnt
pop x3
pop x2
pop x1
pop shift
pop YH
sofError:
pop YL
out SREG, YL
pop YL
reti
#if USB_CFG_HAVE_INTRIN_ENDPOINT && USB_CFG_HAVE_INTRIN_ENDPOINT3
handleIn3: ;1 [38] (branch taken)
lds cnt, usbTxLen3 ;2 [40]
sbrc cnt, 4 ;2 [42]
rjmp sendCntAndReti ;0 43 + 17 = 60 until SOP
sts usbTxLen3, x1 ;2 [44] x1 == USBPID_NAK from above
ldi YL, lo8(usbTxBuf3) ;1 [45]
ldi YH, hi8(usbTxBuf3) ;1 [46]
rjmp usbSendAndReti ;2 [48] + 13 = 61 until SOP (violates the spec by 1 cycle)
#endif
;Setup and Out are followed by a data packet two bit times (16 cycles) after
;the end of SE0. The sync code allows up to 40 cycles delay from the start of
;the sync pattern until the first bit is sampled. That's a total of 56 cycles.
handleSetupOrOut: ;1 [29] (branch taken)
#if USB_CFG_IMPLEMENT_FN_WRITEOUT /* if we have data for second OUT endpoint, set usbCurrentTok to -1 */
sbrc x3, 7 ;1 [30] skip if endpoint 0
ldi token, -1 ;1 [31] indicate that this is endpoint 1 OUT
#endif
sts usbCurrentTok, token;2 [33]
pop cnt ;2 [35]
pop x3 ;2 [37]
pop x2 ;2 [39]
pop x1 ;2 [41]
pop shift ;2 [43]
pop YH ;2 [45]
USB_LOAD_PENDING(YL) ;1 [46]
sbrc YL, USB_INTR_PENDING_BIT;1 [47] check whether data is already arriving
rjmp waitForJ ;2 [49] save the pops and pushes -- a new interrupt is aready pending
rjmp sofError ;2 not an error, but it does the pops and reti we want
handleData: ;1 [15] (branch taken)
lds token, usbCurrentTok;2 [17]
tst token ;1 [18]
breq doReturn ;1 [19]
lds x2, usbRxLen ;2 [21]
tst x2 ;1 [22]
brne sendNakAndReti ;1 [23]
; 2006-03-11: The following two lines fix a problem where the device was not
; recognized if usbPoll() was called less frequently than once every 4 ms.
cpi cnt, 4 ;1 [24] zero sized data packets are status phase only -- ignore and ack
brmi sendAckAndReti ;1 [25] keep rx buffer clean -- we must not NAK next SETUP
sts usbRxLen, cnt ;2 [27] store received data, swap buffers
sts usbRxToken, token ;2 [29]
lds x2, usbInputBufOffset;2 [31] swap buffers
ldi cnt, USB_BUFSIZE ;1 [32]
sub cnt, x2 ;1 [33]
sts usbInputBufOffset, cnt;2 [35] buffers now swapped
rjmp sendAckAndReti ;2 [37] + 19 = 56 until SOP
handleIn: ;1 [25] (branch taken)
;We don't send any data as long as the C code has not processed the current
;input data and potentially updated the output data. That's more efficient
;in terms of code size than clearing the tx buffers when a packet is received.
lds x1, usbRxLen ;2 [27]
cpi x1, 1 ;1 [28] negative values are flow control, 0 means "buffer free"
brge sendNakAndReti ;1 [29] unprocessed input packet?
ldi x1, USBPID_NAK ;1 [30] prepare value for usbTxLen
#if USB_CFG_HAVE_INTRIN_ENDPOINT
sbrc x3, 7 ;2 [33] x3 contains addr + endpoint
rjmp handleIn1 ;0
#endif
lds cnt, usbTxLen ;2 [34]
sbrc cnt, 4 ;2 [36] all handshake tokens have bit 4 set
rjmp sendCntAndReti ;0 37 + 17 = 54 until SOP
sts usbTxLen, x1 ;2 [38] x1 == USBPID_NAK from above
ldi YL, lo8(usbTxBuf) ;1 [39]
ldi YH, hi8(usbTxBuf) ;1 [40]
rjmp usbSendAndReti ;2 [42] + 14 = 56 until SOP
; Comment about when to set usbTxLen to USBPID_NAK:
; We should set it back when we receive the ACK from the host. This would
; be simple to implement: One static variable which stores whether the last
; tx was for endpoint 0 or 1 and a compare in the receiver to distinguish the
; ACK. However, we set it back immediately when we send the package,
; assuming that no error occurs and the host sends an ACK. We save one byte
; RAM this way and avoid potential problems with endless retries. The rest of
; the driver assumes error-free transfers anyway.
#if USB_CFG_HAVE_INTRIN_ENDPOINT /* placed here due to relative jump range */
handleIn1: ;1 [33] (branch taken)
#if USB_CFG_HAVE_INTRIN_ENDPOINT3
; 2006-06-10 as suggested by O.Tamura: support second INTR IN / BULK IN endpoint
ldd x2, y+2 ;2 [35]
sbrc x2, 0 ;2 [37]
rjmp handleIn3 ;0
#endif
lds cnt, usbTxLen1 ;2 [39]
sbrc cnt, 4 ;2 [41] all handshake tokens have bit 4 set
rjmp sendCntAndReti ;0 42 + 17 = 59 until SOP
sts usbTxLen1, x1 ;2 [43] x1 == USBPID_NAK from above
ldi YL, lo8(usbTxBuf1) ;1 [44]
ldi YH, hi8(usbTxBuf1) ;1 [45]
rjmp usbSendAndReti ;2 [47] + 13 = 60 until SOP
#endif
;----------------------------------------------------------------------------
; Transmitting data
;----------------------------------------------------------------------------
bitstuff0: ;1 (for branch taken)
eor x1, x4 ;1
ldi x2, 0 ;1
out USBOUT, x1 ;1 <-- out
rjmp didStuff0 ;2 branch back 2 cycles earlier
bitstuff1: ;1 (for branch taken)
eor x1, x4 ;1
rjmp didStuff1 ;2 we know that C is clear, jump back to do OUT and ror 0 into x2
bitstuff2: ;1 (for branch taken)
eor x1, x4 ;1
rjmp didStuff2 ;2 jump back 4 cycles earlier and do out and ror 0 into x2
bitstuff3: ;1 (for branch taken)
eor x1, x4 ;1
rjmp didStuff3 ;2 jump back earlier and ror 0 into x2
bitstuff4: ;1 (for branch taken)
eor x1, x4 ;1
ldi x2, 0 ;1
out USBOUT, x1 ;1 <-- out
rjmp didStuff4 ;2 jump back 2 cycles earlier
sendNakAndReti: ;0 [-19] 19 cycles until SOP
ldi x3, USBPID_NAK ;1 [-18]
rjmp usbSendX3 ;2 [-16]
sendAckAndReti: ;0 [-19] 19 cycles until SOP
ldi x3, USBPID_ACK ;1 [-18]
rjmp usbSendX3 ;2 [-16]
sendCntAndReti: ;0 [-17] 17 cycles until SOP
mov x3, cnt ;1 [-16]
usbSendX3: ;0 [-16]
ldi YL, 20 ;1 [-15] 'x3' is R20
ldi YH, 0 ;1 [-14]
ldi cnt, 2 ;1 [-13]
; rjmp usbSendAndReti fallthrough
; USB spec says:
; idle = J
; J = (D+ = 0), (D- = 1) or USBOUT = 0x01
; K = (D+ = 1), (D- = 0) or USBOUT = 0x02
; Spec allows 7.5 bit times from EOP to SOP for replies (= 60 cycles)
;usbSend:
;pointer to data in 'Y'
;number of bytes in 'cnt' -- including sync byte
;uses: x1...x4, shift, cnt, Y
;Numbers in brackets are time since first bit of sync pattern is sent
usbSendAndReti: ;0 [-13] timing: 13 cycles until SOP
in x2, USBDDR ;1 [-12]
ori x2, USBMASK ;1 [-11]
sbi USBOUT, USBMINUS;2 [-9] prepare idle state; D+ and D- must have been 0 (no pullups)
in x1, USBOUT ;1 [-8] port mirror for tx loop
out USBDDR, x2 ;1 [-7] <- acquire bus
; need not init x2 (bitstuff history) because sync starts with 0
push x4 ;2 [-5]
ldi x4, USBMASK ;1 [-4] exor mask
ldi shift, 0x80 ;1 [-3] sync byte is first byte sent
txLoop: ; [62]
sbrs shift, 0 ;1 [-2] [62]
eor x1, x4 ;1 [-1] [63]
out USBOUT, x1 ;1 [0] <-- out bit 0
ror shift ;1 [1]
ror x2 ;1 [2]
didStuff0:
cpi x2, 0xfc ;1 [3]
brsh bitstuff0 ;1 [4]
sbrs shift, 0 ;1 [5]
eor x1, x4 ;1 [6]
ror shift ;1 [7]
didStuff1:
out USBOUT, x1 ;1 [8] <-- out bit 1
ror x2 ;1 [9]
cpi x2, 0xfc ;1 [10]
brsh bitstuff1 ;1 [11]
sbrs shift, 0 ;1 [12]
eor x1, x4 ;1 [13]
ror shift ;1 [14]
didStuff2:
ror x2 ;1 [15]
out USBOUT, x1 ;1 [16] <-- out bit 2
cpi x2, 0xfc ;1 [17]
brsh bitstuff2 ;1 [18]
sbrs shift, 0 ;1 [19]
eor x1, x4 ;1 [20]
ror shift ;1 [21]
didStuff3:
ror x2 ;1 [22]
cpi x2, 0xfc ;1 [23]
out USBOUT, x1 ;1 [24] <-- out bit 3
brsh bitstuff3 ;1 [25]
nop2 ;2 [27]
ld x3, y+ ;2 [29]
sbrs shift, 0 ;1 [30]
eor x1, x4 ;1 [31]
out USBOUT, x1 ;1 [32] <-- out bit 4
ror shift ;1 [33]
ror x2 ;1 [34]
didStuff4:
cpi x2, 0xfc ;1 [35]
brsh bitstuff4 ;1 [36]
sbrs shift, 0 ;1 [37]
eor x1, x4 ;1 [38]
ror shift ;1 [39]
didStuff5:
out USBOUT, x1 ;1 [40] <-- out bit 5
ror x2 ;1 [41]
cpi x2, 0xfc ;1 [42]
brsh bitstuff5 ;1 [43]
sbrs shift, 0 ;1 [44]
eor x1, x4 ;1 [45]
ror shift ;1 [46]
didStuff6:
ror x2 ;1 [47]
out USBOUT, x1 ;1 [48] <-- out bit 6
cpi x2, 0xfc ;1 [49]
brsh bitstuff6 ;1 [50]
sbrs shift, 0 ;1 [51]
eor x1, x4 ;1 [52]
ror shift ;1 [53]
didStuff7:
ror x2 ;1 [54]
cpi x2, 0xfc ;1 [55]
out USBOUT, x1 ;1 [56] <-- out bit 7
brsh bitstuff7 ;1 [57]
mov shift, x3 ;1 [58]
dec cnt ;1 [59]
brne txLoop ;1/2 [60/61]
;make SE0:
cbr x1, USBMASK ;1 [61] prepare SE0 [spec says EOP may be 15 to 18 cycles]
pop x4 ;2 [63]
;brackets are cycles from start of SE0 now
out USBOUT, x1 ;1 [0] <-- out SE0 -- from now 2 bits = 16 cycles until bus idle
nop2 ;2 [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
lds x2, usbNewDeviceAddr;2 [4]
subi YL, 20 + 2 ;1 [5]
sbci YH, 0 ;1 [6]
breq skipAddrAssign ;2 [8]
sts usbDeviceAddr, x2;0 if not skipped: SE0 is one cycle longer
skipAddrAssign:
;end of usbDeviceAddress transfer
ldi x2, 1<<USB_INTR_PENDING_BIT;1 [9] int0 occurred during TX -- clear pending flag
USB_STORE_PENDING(x2) ;1 [10]
ori x1, USBIDLE ;1 [11]
in x2, USBDDR ;1 [12]
cbr x2, USBMASK ;1 [13] set both pins to input
mov x3, x1 ;1 [14]
cbr x3, USBMASK ;1 [15] configure no pullup on both pins
out USBOUT, x1 ;1 [16] <-- out J (idle) -- end of SE0 (EOP signal)
out USBDDR, x2 ;1 [17] <-- release bus now
out USBOUT, x3 ;1 [18] <-- ensure no pull-up resistors are active
rjmp doReturn
bitstuff5: ;1 (for branch taken)
eor x1, x4 ;1
rjmp didStuff5 ;2 same trick as above...
bitstuff6: ;1 (for branch taken)
eor x1, x4 ;1
rjmp didStuff6 ;2 same trick as above...
bitstuff7: ;1 (for branch taken)
eor x1, x4 ;1
rjmp didStuff7 ;2 same trick as above...
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