tsb: vendor the fixed-baud assembly oracle as the size/feature bar

The Seed Robotics native-UART fixed-baud TinySafeBoot (GPLv3), reference
only — not built. Assembles to 500 B with the full feature set, proving
≤512 B and full feature parity are simultaneously reachable. Also drops the
stale empty stk500v2/ leftover.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
This commit is contained in:
2026-07-19 15:29:58 +02:00
parent f32a27ff15
commit 04c04abe3e
2 changed files with 823 additions and 0 deletions

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oracle/tsb-fixedbaud.asm Normal file
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;***********************************************************************
;***********************************************************************
;***********************************************************************
; TinySafeBoot - The Universal Bootloader for AVR ATmegas
;***********************************************************************
;***********************************************************************
;***********************************************************************
;
;-----------------------------------------------------------------------
; 2020 - Version using native UART, Fixed Baud by Seed Robotics in 2020
;-----------------------------------------------------------------------
; meant for use on ATMEGA devices only (with native UART - UART0)
;
; Main differences to Regular TSB Bootloader:
; - Uses a native UART (UART0); therefore not compatible with ATTINY
; - Baud rate is fixed (set by a macro in the code). No auto bauding.
; - Disables TX while not transmitting to allow for one wire flashing
; (where RX and TX are shorted, for a multi drop bus)
; - Also works with separate RX and TX; however an external pull up
; on TX _may_ be required; alternatively you can modify the code
; in the ReceiveByte routine so that it won't disable TX.
; - FIXES:
; - situations where booting onto a bus with active communication could
; lock the autobauding feature
; - times out and boots to application code if the host stops interacting
; with the bootloader
;
;-----------------------------------------------------------------------
; Extended by Seed Robotics from 2017
;-----------------------------------------------------------------------
; Seed Robotics contributions are available from the Github
; repository github.com/seedrobotics
; The License and conditions remain as stated below, in the
; original notice.
;
;
;-----------------------------------------------------------------------
; Written in 2011-2015 by Julien Thomas
;
; This program is free software; you can redistribute it and/or
; modify it under the terms of the GNU General Public License
; as published by the Free Software Foundation; either version 3
; of the License, or (at your option) any later version.
; This program is distributed in the hope that it will be useful,
; but WITHOUT ANY WARRANTY; without even the implied warranty
; of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
; See the GNU General Public License for more details.
; You should have received a copy of the GNU General Public License
; along with this program; if not, see:
; http://www.gnu.org/licenses/
;-----------------------------------------------------------------------
;
;
;
;***********************************************************************
; OVERVIEW
;***********************************************************************
;
; TSB assembly source is organized in 4 segments (approx. line numbers)
;
; ~ 50 ... Global definitions
; ~ ... TSB for ATmegas
;
;***********************************************************************
; ADJUSTMENTS FOR INDIVIDUAL ASSEMBLY
;***********************************************************************
;
; This Sourcecode is directly compatible to: AVRASM2, GAVRASM
;
.nolist
;
;-----------------------------------------------------------------------
; SPECIFY TARGET AVR
;-----------------------------------------------------------------------
;
; Comment in and provide def.inc file for target device
;
; [Examples]
;
;.include "tn2313def.inc"
;.include "tn85def.inc"
;.include "m8515def.inc"
;.include "m168def.inc"
;.include "m161def.inc"
;.include "m324Adef.inc"
;.include "m328Pdef.inc"
;.include "tn441def.inc"
;.include "tn167def.inc"
;.include "tn861def.inc"
;.include "tn841def.inc"
;.include "tn84def.inc"
;.include "m8def.inc"
;.include "m644PAdef.inc"
;.include "m644def.inc"
;.include "tn167def.inc"
;.include "tn25def.inc"
;
; [...]
;
;
.list
;
;-----------------------------------------------------------------------
; BUILD INFO
;-----------------------------------------------------------------------
; YY = Year - MM = Month - DD = Day
.set YY = 21
.set MM = 12
.set DD = 21
;
.set BUILDSTATE = $F3 ; F1 fixed baud, pull up, derived from original (modified for fixed baud)
; F2 fixed baud, pull up, guaranteed minimum activation timeout in case of userpage data corruption
; F3 adds a CONSTANT with clock speed (Mhz) as word in the last page of memory (clock speed our defined CONSTANT)
;
;-----------------------------------------------------------------------
; TSB / TSB-INSTALLER SWITCH
;-----------------------------------------------------------------------
; 0 = Regular assembly to target address
; Other value = NOT SUPPORTED
;
.set TSBINSTALLER = 0
;
;-----------------------------------------------------------------------
; F_CPU and Baud rate setting
;-----------------------------------------------------------------------
.equ F_CPU = 20000000
.equ BAUD = 33333 ; baudrate (notice some possible wrong cals: example for 56K, it is actually 55,555, so for BAUD_PRESC give an INT result of 8, we must set BAUD to 55500)
.equ BAUD_PRESCx10 = (F_CPU * 10/16/BAUD) - 10 ; baud prescale (regular formula = F_CPU * 10/16/BAUD - 1 but we do it x10 to check the rounding)
; arredondar acima se necesssario
.if BAUD_PRESCx10 - ( (BAUD_PRESCx10 / 10) * 10 ) >= 5 ; calculate the remainder: we rely on the fact these are integer divisions. Therefore, dividing by 10, rounds DOWN in integer division
.equ BAUD_PRESC = (F_CPU/16/BAUD)
.warning "Incrementing default BAUD_PRESC formula by 1 due to rounding."
.else
.equ BAUD_PRESC = (F_CPU/16/BAUD) - 1
.warning "Using default BAUD_PRESC formula (no rounding up)"
.endif
.if BAUD_PRESC > 255
.error "ERROR: BAUD RATE TOO LOW. WE ONLY WRITE THE UBRRL REGISTER, SO UBRR MUST BE <255 FOR THIS CLOCK FREQ AND BAUD"
.endif
;***********************************************************************
; AUTO-ADJUST FOR DIFFERENT ASSEMBLY OPTIONS
;***********************************************************************
;
; Always set TINYMEGA=1 bc this code only supports ATMEGA
.equ TINYMEGA=1
.if FLASHEND > ($7fff)
.error "SORRY! DEVICES OVER 64 KB NOT SUPPORTED YET."
.exit
.endif
;-----------------------------------------------------------------------
; Workarounds for devices with renamed or missing definitions
;-----------------------------------------------------------------------
;
.ifndef SPMCSR ; SPMEN / PGERS / ...
.equ SPMCSR = SPMCR
.endif
.ifndef MCUSR ; PORF / EXTRF / BORF / WDRF
.equ MCUSR = MCUCSR
.endif
; Detect Attiny441/841 to amend missing pagesize and apply 4-page mode
.set FOURPAGES = 0
.if ((SIGNATURE_000 == $1E) && (SIGNATURE_002 == $15) && (SIGNATURE_001 == $92))
.equ PAGESIZE = 32
.set FOURPAGES = 1
.message "ATTINY441: 4-PAGE-ERASE MODE"
.endif
.if ((SIGNATURE_000 == $1E) && (SIGNATURE_002 == $15) && (SIGNATURE_001 == $93))
.equ PAGESIZE = 32
.set FOURPAGES = 1
.message "ATTINY841: 4-PAGE-ERASE MODE"
.endif
;-----------------------------------------------------------------------
; Universal Constants and Registers
;-----------------------------------------------------------------------
.equ REQUEST = '?' ; request / answer / go on
.equ CONFIRM = '!' ; confirm / attention
; Current bootloader date coded into 16-bit number
.equ BUILDDATE = YY * 512 + MM * 32 + DD
; Other
.equ INFOLEN = 8 ; *Words* of Device Info
.equ BUFFER = SRAM_START
; Registers (in use by TSB-Firmware and TSB-Installer for ATtinys)
.def avecl = r4 ; application vector temp low
.def avech = r5 ; application vector temp high
.def tmp1 = r16 ; these are
.def tmp2 = r17 ; universal
.def tmp3 = r18 ; temporary
.def tmp4 = r19 ; registers
.def bcnt = r20 ; page bytecounter
.def cntr1 = r21 ; timeout counter
.def rxen = r22 ; check if RX enabled (meaning TX disabled)
.def utimeoutH = r23 ; user timeout High byte
; special purpose registers start at R26
;
;
;***********************************************************************
;***********************************************************************
;***********************************************************************
; START OF TSB FOR ATMEGAS
;***********************************************************************
;***********************************************************************
;***********************************************************************
;
; TSB for ATmegas is always coded directly to target address.
.if TINYMEGA == 1
.message "ASSEMBLY OF TSB FOR ATMEGA"
.equ BOOTSTART = (FLASHEND+1)-256 ; = 512 Bytes
.equ LASTPAGE = BOOTSTART - PAGESIZE ; = 1 page below TSB!
.org BOOTSTART
RESET:
cli
in tmp4, MCUSR ; check reset condition
sbrc tmp4, WDRF ; in case of a Watchdog reset
rjmp APPJUMP ; immediately leave TSB
ldi tmp1, low (RAMEND) ; write ramend low
out SPL, tmp1 ; into SPL (stackpointer low)
.ifdef SPH
ldi tmp1, high(RAMEND) ; write ramend high for ATtinys
out SPH, tmp1 ; with SRAM > 256 bytes
.message "PROVIDING FOR STACK BIGGER THAN 256 BYTES"
.endif
.ifndef DDRD2
.equ DDRD2 = DDD2
.endif
;-----------------------------------------------------------------------
; ACTIVATION CHECK
;-----------------------------------------------------------------------
; Configure UART; no autobauding in this version
ldi tmp1,BAUD_PRESC ; load baud prescale
sts UBRR0L,tmp1 ; set baud prescale
; ldi tmp2,HIGH(bpsc) ; save code by not loading UBBRH
;sts UBRRH,tmp2 ; to UBRR0
;ldi tmp2,( (1<<RXEN0) ) ; enable transmiter and receiver
;sts UCSR0B,tmp2
; Enable Pull up on Port D2 (PD2)
cbi DDRD, DDRD2
sbi PORTD, PORTD2
; we will enable RNEN/TXEN in the ReceiveByte and TransmitByte routines
rcall ZtoLASTPAGE ; set Z to start'o'LASTPAGE
adiw zl, 2 ; skip first 2 bytes (APPJUMP)
lpm utimeoutH, z+ ; load TIMEOUT byte and store for use in RX byte timeout
ori utimeoutH, (F_CPU / 1000000); prevent bootloader lockout due if it gets an invalid (to small) timeout setting
; this ensures value is at least the clock rate, which shoudl give about 40ms
clr tmp2 ; apparently at times this is not set to 0 on boot? (seen while in debugWire)
clr rxen ; same as above
WRX1To:
; we'll check the X register which is where ReceibeByte controls the timeout
; the overall timeout of receive byte is the timeout set by the user
; therefore, if we get characters while X> 0 we're attempting to activate bootloader;
; if not, if X=0 we timedout and go to app start
rcall ReceiveByte
brcs WRX2To ; if X got to 0 (i.e. carry set), assume we timed out
cpi tmp1, '@' ; did we get an activation char = "@"
breq ActCharRcvd
WRX2To:
rjmp APPJUMP ; not an activation char goto APPJUMP in LASTPAGE
ActCharRcvd:
inc tmp2
cpi tmp2, 3
brne WRX1To ; branch if not yet at 3;
; otherwise fall through to password check
;-----------------------------------------------------------------------
; CHECK PASSWORD / EMERGENCY ERASE
;-----------------------------------------------------------------------
; we use the user timeout (utimeoutH) register for COMM timeout
; when we don't get valid data
; increase this value to a fixed one now, to cope
; with cases where the user timeout is set so low that we don't have time to
; do anything
ldi utimeoutH, (F_CPU / 78500) ; this should result in 255 for 20Mhz and proportionally
; less for lower Clocks, so that we get the same time approx. 2.4sec
CheckPassword:
chpw0: ser tmp4 ; tmp4 = 255 enables comparison
chpw1: lpm tmp3, z+ ; load pw character from Z
and tmp3, tmp4 ; if tmp4 = 0 disables comparison, for wrong password scenarios
cpi tmp3, 255 ; byte value 255 indicates
breq chpwx ; end of password -> success
chpw2: rcall Receivebyte ; else receive next character
cpi tmp1, 0 ; rxbyte = 0 will branch
breq chpwee ; to confirm emergency erase
cp tmp1, tmp3 ; compare password with rxbyte
breq chpw0 ; if equal check next character
clr tmp4 ; tmp4 = 0 to loop forever
rjmp chpw1 ; and smoothen power profile
chpwee:
; Fix for ISSUE #1: only check for Emergency Erase if we haven't
; gotten a wrong password; if we got a wrong password
; then we should stay in loop and not escape to Emergency
; Erase
cpi tmp4, 0 ; if tmp4=0 we are set to loop forever
breq chpw1
rcall RequestConfirm ; request confirm
brts chpa ; not confirmed, leave
rcall RequestConfirm ; request 2nd confirm
brts chpa ; can't be mistake now
rcall EmergencyErase ; go, emergency erase!
rjmp Mainloop
chpa:
rjmp APPJUMP ; start application
chpwx:
; rjmp SendDeviceInfo ; go on to SendDeviceInfo
;-----------------------------------------------------------------------
; SEND DEVICEINFO
;-----------------------------------------------------------------------
SendDeviceInfo:
ldi zl, low (DEVICEINFO*2) ; load address of deviceinfo
ldi zh, high(DEVICEINFO*2) ; low and highbyte
ldi bcnt, INFOLEN*2
rcall SendFromFlash
;-----------------------------------------------------------------------
; MAIN LOOP TO RECEIVE AND EXECUTE COMMANDS
;-----------------------------------------------------------------------
Mainloop:
clr zl ; clear Z pointer
clr zh ; which is frequently used
rcall SendConfirm ; send CONFIRM via RS232
rcall Receivebyte ; receive command via RS232
rcall CheckCommands ; check command letter
rjmp Mainloop ; and loop on
;-----------------------------------------------------------------------
; CHANGE USER DATA IN LASTPAGE
;-----------------------------------------------------------------------
ChangeSettings:
rcall GetNewPage ; get new LASTPAGE contents
brtc ChangeS0 ; from Host (if confirmed)
ret
ChangeS0:
rcall ZtoLASTPAGE ; re-write LASTPAGE
rcall EraseFlashPage
rcall WritePage ; erase and write LASTPAGE
;-----------------------------------------------------------------------
; SEND USER DATA FROM LASTPAGE
;-----------------------------------------------------------------------
ControlSettings:
rcall ZtoLASTPAGE ; point to LASTPAGE
; rcall SendPageFromFlash
;-----------------------------------------------------------------------
; SEND DATA FROM FLASH MEMORY
;-----------------------------------------------------------------------
SendPageFromFlash:
ldi bcnt, low (PAGESIZE*2) ; whole Page to send
SendFromFlash:
rcall SPMwait ; (re)enable RWW read access
lpm tmp1, z+ ; read directly from flash
rcall Transmitbyte ; and send out to RS232
dec bcnt ; bcnt is number of bytes
brne SendFromFlash
ret
;-----------------------------------------------------------------------
; READ APPLICATION FLASH
;-----------------------------------------------------------------------
; read and transmit application flash area (pagewise)
ReadAppFlash:
RAF0:
rcall RwaitConfirm
brts RAFx
rcall SendPageFromFlash
RAF1:
cpi zl, low (LASTPAGE*2) ; count up to last byte
brne RAF0 ; below LASTPAGE
cpi zh, high(LASTPAGE*2)
brne RAF0
RAFx:
ret
;-----------------------------------------------------------------------
; WRITE APPLICATION FLASH
;-----------------------------------------------------------------------
; Write Appflash pagewise, don't modify anything for ATmegas
WriteAppFlash:
rcall EraseAppFlash ; Erase whole app flash
Flash2:
rcall GetNewPage ; get next page from host
brts FlashX ; stop on user's behalf
Flash3:
rcall WritePage ; write page data into flash
Flash4:
cpi zh, high(LASTPAGE*2-1) ; end of available Appflash?
brne Flash2 ; if Z reached last location
cpi zl, low (LASTPAGE*2-1) ; then we are finished
brne Flash2 ; else go on
FlashX:
ret ; we're already finished!
;-----------------------------------------------------------------------
; WRITE FLASH PAGE FROM BUFFER, VERIFYING AND VERIFY-ERROR-HANDLING
;-----------------------------------------------------------------------
WritePage:
rcall YtoBUFFER ; Y=BUFFER, bcnt=PAGESIZE*2
WrPa1:
ld r0, y+ ; fill R0/R1 with word
ld r1, y+ ; from buffer position Y / Y+1
ldi tmp1, 0b00000001 ; set only SPMEN in SPMCSR
out SPMCSR, tmp1 ; to activate page buffering
spm ; store word in page buffer
adiw zl, 2 ; and forward to next word
subi bcnt, 2
brne WrPa1
; Z = start of next page now
subi zl, low (PAGESIZE*2) ; point back Z to
sbci zh, high(PAGESIZE*2) ; start of current page
; Z = back on current page's start
WrPa2:
ldi tmp1, 0b00000101 ; enable PRWRT + SPMEN
out SPMCSR, tmp1 ; in SPMCSR
spm ; write whole page to flash
WrPa3:
in tmp1, SPMCSR ; wait for flash write finished
sbrc tmp1, 0 ; skip if SPMEN (bit0) cleared
rjmp WrPa3 ; ITS BEEN WRITTEN
subi zl, low (-PAGESIZE*2) ; same effect as
sbci zh, high(-PAGESIZE*2) ; Z = Z + PAGESIZE*2
ret
;-----------------------------------------------------------------------
; CHECK COMMANDS
;-----------------------------------------------------------------------
CheckCommands:
cpi tmp1, 'c' ; read LASTPAGE
breq ControlSettings
cpi tmp1, 'C' ; write LASTPAGE
breq ChangeSettings
cpi tmp1, 'f' ; read Appflash
breq ReadAppFlash
cpi tmp1, 'F' ; write Appflash
breq WriteAppFlash
cpi tmp1, 'e' ; read EEPROM
breq EepromRead
cpi tmp1, 'E' ; write EEPROM
breq EEpromWrite
rjmp APPJUMP ; else start application
;-----------------------------------------------------------------------
; EEPROM READ/WRITE ACCESS
;-----------------------------------------------------------------------
EepromWrite:
EEWr0:
rcall GetNewPage ; get EEPROM datablock
brts EERWFx ; or abort on host's demand
EEWr1:
rcall YtoBUFFER ; Y = Buffer and Bcnt = blocksize
EEWr2:
ld tmp1, y+ ; read EEPROM byte from buffer
rcall EEWriteByte
dec bcnt ; count down block byte counter
brne EEWr2 ; loop on if block not finished
rjmp EeWr0
;-----------------------------------------------------------------------
EEpromRead:
EeRe1:
rcall RwaitConfirm ; wait to confirm
brts EERWFx ; else we are finished
ldi bcnt, low(PAGESIZE*2) ; again PAGESIZE*2 is blocksize
EERe2:
out EEARL, zl ; current EEPROM address low
.ifdef EEARH
out EEARH, zh ; current EEPROM address high
.endif
sbi EECR, 0 ; set EERE - EEPROM read enable
in tmp1, EEDR ; read byte from current address
rcall Transmitbyte ; send out to RS232
adiw zl,1 ; count up EEPROM address
dec bcnt ; count down block byte counter
brne EERe2 ; loop on if block not finished
rjmp EERe1
EERWFx:
ret
;-----------------------------------------------------------------------
EEWriteByte:
out EEDR, tmp1 ; write to EEPROM data register
out EEARL, zl ; current EEPROM address low
.ifdef EEARH
out EEARH, zh ; high EEARH for some attinys
.endif
sbi EECR, 2 ; EEPROM master prog enable
sbi EECR, 1 ; EEPE initiate prog cycle
EeWB:
sbic EECR, 1 ; wait write cycle to complete
rjmp EeWB ; before we can go on
adiw zl,1 ; count up EEPROM address
ret
;-----------------------------------------------------------------------
; GET NEW PAGE
;-----------------------------------------------------------------------
GetNewPage:
rcall RequestConfirm ; check for Confirm
brts GNPx ; abort if not confirmed
GNP0:
rcall YtoBUFFER ; Y = BUFFER, bcnt = PAGESIZE*2
GNP1:
rcall ReceiveByte ; receive serial byte
st y+, tmp1 ; and store in buffer
dec bcnt ; until full page loaded
brne GNP1 ; loop on
GNPx:
ret ; finished
;-----------------------------------------------------------------------
; REQUEST TO CONFIRM / AWAIT CONFIRM COMMAND
;-----------------------------------------------------------------------
RequestConfirm:
ldi tmp1, REQUEST ; send request character
rcall Transmitbyte ; prompt to confirm (or not)
RwaitConfirm:
rcall ReceiveByte ; get host's reply
clt ; set T=0 for confirmation
cpi tmp1, CONFIRM ; if host HAS sent CONFIRM
breq RCx ; return with the T=0
set ; else set T=1 (NOT CONFIRMED)
RCx:
ret ; whether confirmed or not
;-----------------------------------------------------------------------
; FLASH ERASE TOP-TO-BOTTOM ( (BOOTSTART-1) ... $0000)
;-----------------------------------------------------------------------
EraseAppFlash:
rcall ZtoLASTPAGE ; point Z to LASTPAGE, directly
EAF0:
subi zl, low (PAGESIZE*2)
sbci zh, high(PAGESIZE*2)
rcall EraseFlashPage
brne EAF0 ; until first page reached
EAFx: ret ; and leave with Z = $0000
;-----------------------------------------------------------------------
; EMERGENCY ERASE OF FLASH / EEPROM / USERDATA
;-----------------------------------------------------------------------
EmergencyErase:
rcall EraseAppFlash ; erase Application Flash
ser tmp1 ; byte value for EEPROM writes
EEE0:
rcall EEWriteByte ; write EEPROM byte, Z = Z + 1
cpi zh, high(EEPROMEND+1)+2 ; EEPROMEND
brne EEE0 ; and loop on until finished
rcall ZtoLASTPAGE ; LASTPAGE is to be erased
; rcall EraseFlashPage
;-----------------------------------------------------------------------
; ERASE ONE FLASH PAGE
;-----------------------------------------------------------------------
EraseFlashPage:
ldi tmp1, 0b00000011 ; enable PGERS + SPMEN
out SPMCSR, tmp1 ; in SPMCSR and erase current
spm ; page by SPM (MCU halted)
; Waiting for SPM to be finished is *obligatory* on ATmegas!
SPMwait:
in tmp1, SPMCSR
sbrc tmp1, 0 ; wait previous SPMEN
rjmp SPMwait
ldi tmp1, 0b00010001 ; set RWWSRE and SPMEN
out SPMCSR, tmp1
spm
ret
;-----------------------------------------------------------------------
; OTHER SUBROUTINES
;-----------------------------------------------------------------------
YtoBUFFER:
ldi yl, low (BUFFER) ; reset pointer
ldi yh, high(BUFFER) ; to programming buffer
ldi bcnt, low(PAGESIZE*2) ; and often needed
ret
;-----------------------------------------------------------------------
ZtoLASTPAGE:
ldi zl, low (LASTPAGE*2) ; reset Z to LASTPAGE start
ldi zh, high(LASTPAGE*2)
ret
;-----------------------------------------------------------------------
; RS232 RECEIVE BYTE
;-----------------------------------------------------------------------
; uses: tmp1 (received data byte), cntr1 (for timeout)
; also uses utimeoutH which holds the default timeout defined by the user
; and X which is actually used to count down
SetRX:
ldi tmp1,(1<<RXEN0) ; enable receiver (Transmitter disabled)
sts UCSR0B,tmp1
ser rxen
ReceiveByte:
sbrs rxen, 0
rjmp SetRX
; outer counter
mov xh, utimeoutH
;ldi xl, 128
ReceiveByteShortTimeout:
ser cntr1 ; inner counter reset
ReceiveByteShortTimeout1:
lds tmp1, UCSR0A ; load UART status register A
sbrc tmp1, RXC0 ; if not RXComplete, skip
rjmp LoadRXByte
dec cntr1 ; if counter not zero
brne ReceiveByteShortTimeout1 ; cycle again; else fall through
sbiw xl, 1 ; dec outter counter
brcc ReceiveByteShortTimeout ; continue of outter counetr still active
;ret ;
LoadRXByte:
lds tmp1, UDR0 ; load received character even if RXC is not set
ret ; (it loads 0 and UDR FIFO should recover for next char)
;-----------------------------------------------------------------------
; RS232 SEND CONFIRM CHARACTER
;-----------------------------------------------------------------------
SendConfirm:
ldi tmp1, CONFIRM
rjmp Transmitbyte
;-----------------------------------------------------------------------
; RS232 TRANSMIT BYTE
;-----------------------------------------------------------------------
; uses: tmp1 (transmit byte will be shifted out), tmp2 (bitcounter)
;
SetTX:
ldi tmp2,(1<<TXEN0) ; enable transmitter (Receiver disabled)
sts UCSR0B,tmp2
clr rxen
; wait some guard time to allow receiving devices ot transition
; from TX t RX state
ser cntr1 ; inner counter reset
SetTXShortTimeout:
nop
dec cntr1 ; if counter not zero
brne SetTXShortTimeout ; cycle again; else fall through
TransmitByte:
sbrc rxen, 0
rjmp SetTX
; no need to wait for UDRE bc we will wait for TXC on
; every char transmitted. TXC occurs later that UDRE
; so UDRE should be asserted when TXC asserts
sts UDR0, tmp1
WaitForTXC:
lds tmp2, UCSR0A ; wait for TXC (and not UDRE)
sbrs tmp2, TXC0 ; bc after this char we may transition
rjmp WaitForTXC ; to receiving chars and we want to make sure we get a clean transition
; we need to write a 1 to clear the TXC flag; otherwise the flag won't clear
sts UCSR0A, tmp2 ; tmp2 should contain an asserted TXC bit
ret
;-----------------------------------------------------------------------
; ATMEGA APPJUMP = SIMPLE JUMP TO $0000 (ORIGINAL RESET VECTOR)
;-----------------------------------------------------------------------
; Boot Reset Vector (BOOTRST) must be activated for TSB on ATmegas.
; After timeout or executing commands, TSB for ATmegas will simply
; handover to the App by a (relative or absolute) jump to $0000.
APPJUMP:
rcall SPMwait ; make sure everything's done
.if FLASHEND >= ($1fff)
jmp $0000 ; absolute jump
.else
rjmp $0000 ; relative jump
.endif
DEVICEINFO:
.message "DEVICE INFO BLOCK FOR ATMEGA"
.db "TSB", low (BUILDDATE), high (BUILDDATE), BUILDSTATE
.db SIGNATURE_000, SIGNATURE_001, SIGNATURE_002, low (PAGESIZE)
.dw BOOTSTART-PAGESIZE
.dw EEPROMEND
.db $AA, $AA
;-----------------------------------------------------------------------
; DEVICE INFO BLOCK = PERMANENT DATA
;-----------------------------------------------------------------------
; set last word with the clock speed
.org FLASHEND
.dw (F_CPU/1000000)
//.message "SAVING CLOCK SPEED IN LAST BYTE AS " (F_CPU/1000000) " Mhz"
.message "ASSEMBLY OF TSB FOR ATMEGA SUCCESSFULLY FINISHED!"
.endif ; closing TSB for ATmega sourcecode;
;***********************************************************************
; END OF TSB FOR ATMEGAS
;***********************************************************************
.exit
;***********************************************************************
;***********************************************************************
;***********************************************************************
; END OF CONDITIONAL ASSEMBLY SOURCE OF TSB FOR ATTINYS AND ATMEGAS
;***********************************************************************
;***********************************************************************
;***********************************************************************