Hello, all.
I've been playing around with buspirate and my uISP ( https://github.com/uISP/ ) dongle. Even with newer firmware buspirate is really slow, and on average, takes 3m 49s to read out a 2MiB SPI flash.
So I decided to play around and see if I can make a faster programmer with my uISP dongle. Basically it's an atmega8 with 12M crystal running vusb stack (no hardware usb). Any other similar hardware would do. This hardware is really cheap (BOM is less than 5$ including the pcb).
My first attempt was creating a serprog-compatible firmware for uISP. It can be found here:
https://github.com/uISP/uisp-app-serprog
The results weren't very exciting. It took 4m 30s to read out a 2MiB SPI flash (EN25QH16) on 12M crystal. Same for 20M crystal. It seems like it was a limitation of bulk out transfers via vusb.
The second attempt required patching flashrom itself, but resulted in a MUCH simpler firmware that fits roughly 115 lines of code (not counting vusb). It just uses control transfers for both reads and writes. With vusb long transfers enabled, 20Mhz crystal, 10Mhz SPI speed and max_data_read/max_data_write set to 4096 bytes reading a 2MiB SPI flash took only 2m 13s which I consider a WIN.
4096 is not a vusb limit. USB spec limits maximum transfers to control endpoint to 4096 bytes anyway.
Using 254 byte max_data_read/max_data_write and long transfers disabled would be slower, but it is possible to fit everything into 2K flash and use some attiny2313, which will make it even cheaper. The protocol's simple as hell, so anyone with a better hardware around (STM32, atmega8u2, pic32, whatever) can implement it with very little effort and get lighting-fast speeds. My WIP patch to flashrom's attached, although I have a few silly questions left:
* Do I need to implement SPI frequency changing via a dedicated command or is it okay to hardcode it to 10Mhz in firmware? * Right now I'm using the same spi_read as serprog does. Is okay, or should I add an option to disable it? * firmware version checking, etc. (Is it a good idea to implement?) * Is there a better way to benchmark read/write speed in flashrom, since delay loop calibration interferes with speed measurements (currently I just used "time flashrom ...")