ATMEL AVR UART Bootloader for AVR-GCC/avr-libc
based on the AVR Butterfly bootloader code
by Martin Thomas, Kaiserslautern, Germany
This is an adapted version which has been tested
with the ATmega16 but should work with the ATmega8,
ATmega169 and ATmega32. The bootloader uses block/
page write for flash and is fast.
7. Apr. 2004 - Version 0.5
* added different startup-methods
* compatible with ATmega8 now
* included makefile adopted to ATmega8 now
(ATmega16 options still available)
* fixed jump to application which did not work
* tested with ATmega8
* minimal options and startup-code result in
bootloader-size < 512 words
6. Apr. 2004 - Version 0.4
* Buffered read of chars from UART during programming
since eeprom-write is too slow for unbuffered
operation. So EEPROM-upload does work now.
* Added BOOTICE-mode to flash JTAGICE-compatible
hardware (ATmega16@7,3Mhz) (if you know about BOOTICE,
you may unterstand why this has been added, if not
just keep the option disabled)
* small changes in (my)boot.h (lock-bit-mask) found
out during the development of the STK-500-compatible
bootloader. But setting lock-bits still does not
work with this bootloader.
* read of the low-fuse byte works (high byte still TODO)
* read of the lock-byte works (write still TODO)
27. Mar 2004 - Version 0.3
Felt that as much functions from avr-libc's boot.h
as possible should be used without modifications.
Latest CVS-version of boot.h is included.
Only the read-routine is still "self-made" based
on ATMELs assembler-code.
EEPROM write on Mega16 does not work (and did not
work with V0.2 too). May be caused by my old Mega16
chip. Needs testing. Flash read/write and EEPROM
read works. Still only tested with ATmega16.
This version may not work with the ATmega169 any
24. Mar 2004 - Version 0.2
During the development of a data-logger application
with the AVR-Butterfly there was a need to make
some changes in the bootloader. The same problem
again: no IAR compiler. The same way to solve the
problem: a port of the code to avr-gcc/avr-libc.
So this code is based on the ATMEL Butterfly
bootloader source code Rev 0.2 for IAR.
The bootloader-port for the Butterfly which mimics
the complete functionality of the original
BF-bootloader is availabe at:
Atmel used a separate "lib" written in "pure"
assembly to access the low-level functions
for flash read/write. Well, so far I
don't know how to use "mixed language sources"
with the avr-gcc toolchain, so the low-level
routines have been implemented as inline assembler.
The avr-libc boot.h module written by Eric
Weddington served as a template Three of the four
low-level routines found in lowlevel.c come from
boot.h with minimal changes. The read routine has
been developed based on the ATMEL assembler code.
Ignore the fuse and lock-bit readout. Read and Set is
not enabled (TODO).
--------------- Installation -----------------
- Change the MCU type in the makefile (so far
ATmega16 has been tested, ATmega169, ATmega8
and ATmega32 should be o.k. too.
- Change the boot(loader)-size in main.c, this
bootloader is larger than 512 words (1024 bytes),
so select at least _B1024!
- Change the XTAL in main.c to the clock-frequency
of your board (keep BAUDRATE at 19200). See
the datasheet for frequencies with minimum
error at 19200bps and select Crystal/Oscillator
to get minimum errors.
- Change the start-condition in main.c. Default
is: enter bootloader if Pin A7 is connected to
GND during reset/startup
- Edit the value MT_BOOTLOADER_ADDRESS in the
makefile according to the selected bootloader
size. Keep in mind that this value has to be
given in bytes (not words) in the linker options.
i.e. ATMega16, boot-size 1024 words, see
datasheet and find "Boot Reset Adress" for
"Boot Size" 1024 words is 1C00. 1C00 is given
in words, so set MT_BOOTLOADER_ADDRESS to
- Please use at least avr-gcc 3.3.1/avr-libc 1.0
or WINAVR Sept. 2003 or later to compile and link
- upload the hex-File to the AVR (STK500, STK200, SP12
- program the "Boot Flash section size" (BOOTSZ fuses)
according to the boot-size selected in main.c
i.e. BOOTSZ=00 for boot-size 1024 words on ATmega16
- enable the BOOT Reset Vector (BOOTTRST=0)
- Set the lock bits to protect the bootloader from
SPM-writes (Boot Loader Protection Mode 2 in STK500-
- Connect the AVR UART Pins via level-shifter/inverter
(i.e. MAX232) to you PCs Com-Port.
- Reset the AVR while fullfilling the bootloader start-
condition. Which means connect PA7 to GND in the default
config during reste/power-cycle. Keep the connection
or hold the key down until you see the AVRPROG dialog!
- Start AVRPROG (AVRStuido/Tools or stand-alone) -
keep PA7 grounded!
- AVRPROG will detect the bootloader, you may release
- see AVRStuido online-help for more information how
to use AVRPROG
- make sure to EXIT from AVRPROG (button) to start
your main-application (or toogle power/reset)
good luck, feedback welcome.