You will probably want to clone the repository https://github.com/efabless/caravel_board . In that repository, find the python script

firmware/util/caravel_hkflash.py

, which will flash a hex file to the SPI flash chip using pass-through mode. The basics of pass-through mode is pretty simple: Just send the command byte

0xc4

to Caravel's housekeeping SPI, and then all data after that is communicating directly with the SPI flash until you raise CSB. Every command done that way has to be prefixed with the

0xc4

command.

This is an example bit of code I wrote that runs a simple test to check the GPIOs under management control. Configuring GPIOs 19 to 37 is straightforward. Configuring GPIOs 0 to 18 requires using the script

slippage.py

that I posted in my conversation above with Weston. I plug in the hex values I want the GPIOs to be set to, and the script gives me back the values I need to set the registers to, to get that result. For management-controlled modes, the SoC checks the local value of the configuration, so I have to rewrite all the configuration values after I do the transfer. For user-controlled modes, that's not necessary. Also, due to the bit slipping, there are some limitations on what modes neighboring GPIOs can be set to; again, the user controlled modes don't have those limitations.

Note that the

caravel_board

repository also has a few (less complicated) examples under the

firmware/

directory. I just created a new directory called

benchtest

, copied the Makefile from the

blink

directory, and changed "blink" to "benchtest" as needed.