======================================================

  ATMEL AVR UART Bootloader for AVR-GCC/avr-libc
  based on the AVR Butterfly bootloader code

  by Martin Thomas, Kaiserslautern, Germany
  mthomas@rhrk.uni-kl.de 
  eversmith@heizung-thomas.de

  http://www.siwawi.arubi.uni-kl.de/avr_projects

======================================================


18. Aug. 2005 - Version 0.74

* AT90CAN128 support contributed by Uwe Bonnes
* Makefile modifications contributed by Uwe Bonnes

23. Feb. 2005 - Version 0.7

* (Version 0.6 has never been available on the web-page)
* ATmega128 support
* code cleanup
* Tested with ATmega8, ATmega32 and ATmega128

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
  reliably before
* 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 
more.

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:
www.siwawi.arubi.uni-kl.de/avr_projects

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 Makefile, this
  bootloader is larger than 512 words (1024 bytes), 
  so select at least _B1024!

- Change the XTAL in Makefile 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 Makefile. Default
  is: enter bootloader if Pin A7 is connected to
  GND during reset/startup

- Please use at least avr-gcc 3.3.1/avr-libc 1.0 
  or WINAVR Sept. 2003 or later to compile and link 
  the bootloader.

- upload the hex-File to the AVR (STK500, STK200, SP12
  etc.)

- 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-
  plugin)

- 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
  PA7 now

- 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.
Martin