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

[Johnathan Corgan]

Michael Holzt wrote:

> As you've probably seen, i'm currently working on adding serial bitbang and
> moving bitbang code into a more general approach. It might be a good idea to
> add your adapter as just another flavor of bitbanging...

I haven't looked at your patch yet, but I suspect there would be a 
"abstraction mismatch" with how my code works.  See my previous post on 
how the bit banging mode of the FT232BM is designed.  One doesn't toggle 
bits so much as build a buffer of data to send as a batch.

The lowest level primitive in my library is 'ftavr_send_32bits_fast' 
which builds a 64 byte buffer, based on a supplied 32 bit command value, 
to send over the USB bit banged  This is used for sending commands one 
at a time, when one doesn't need to read the result, e.g., erase_chip().

Another one is 'ftavr_send_32_slow', which sends 32 bits over SPI and 
returns the value clocked out by the AVR.  This is very slow over USB 
but is how commands like set_spi_pgm_mode(), read_signature_byte(), 
read_fuse_bits_low(), etc., are implemented.

I'm in the middle of implementing an arbitrary length data send, which 
expands a supplied buffer of data into the necessary bit bang bytes (per 
my previous email) and sends them over USB.  This would be the case if 
you wanted to send multiple commands back-to-back with no delay in between.

> Do you have some working code and schematic of your approach?

Working code, yes.  The schematic is basically the FT232BM reference 
design with TXD, RXD, RTS, and DTR pins wired to an ATMega8 MISO, MOSI, 
SCLK, and RESET pins.

-Johnathan