[avrdude-dev] Serial programming AVR with FTDI FT232BM Bit Bang Mode

[Johnathan Corgan]

This is my first AVR project.

I have built a board which uses an ATMega8 and an FTDI FT232BM USB to 
serial converter chip.

For normal operation, the FT232BM serial TXD and RXD are routed to the 
appropriate serial port pins on the ATMega8.

For programming, I have routed four pins from the FT232BM to RESET, 
MISO, MOSI, and SCLK, so I can use the bit bang mode of the part for 
programming operations.

I have started work on a programming library under Windows with Cygwin, 
that encapsulates the FTDI driver DLL with the routines for sending and 
receiving data over the SPI interface.  I've verified I can put the 
ATMega8 into serial programming mode, read the device signature, erase 
the chip, and read/write fuse bits.  So I'm pretty confident the 
low-level SPI interface works well.

At this point, I was going to start building actual Flash and EEPROM 
programming routines.  The end goal would be a standalone "updater" 
program specifically for the project/device I'm building.

However, might it be possible to modify avrdude to use my routines for 
the low-level SPI protocol?  I'd avoid massively reinventing the wheel...

I don't have any experience with avrdude itself, this being my first AVR 
project.  Nor would I have any familiarity with the avrdude source code 
structure, or how it might be modularized to accommodate replacing its 
existing low-level routines with mine.  (Of course I have a long 
background in C programming and microcontrollers, just new to AVR and 
avrdude.)

Right now, my library is hard coded for the ATMega8 and the particular 
pin mapping from the FT232BM USB chip to the SPI interface.  It would be 
fairly easy to make the pin mapping configurable.

Anyway, I'm at a point where I need to decide what is easier:  write my 
own special purpose, limited functionality programmer on top of my 
library, or figure out how to add my library to avrdude and get all the 
creamy richness of a mature programmer code base.  If I did the latter 
then my "updater" program would simply be a script that invokes avrdude 
with the right command line parameters.

Suggestions?

-Johnathan