max3421e <> Flipper Zero (STM32WB55RG)

[zacharyweiss]

Howdy!

I'm new to embedded development, and currently drinking from the firehose of topics, so apologies if this is a misguided line of questions.

I'm interested in building a USB host module for the Flipper Zero (based on the STM32WB55RG), and the max3421e seems a fitting option for this, which I see this project has implemented code for. As far as I understand from a skim of the docs / discussions / code, it seems you implement the SPI functions on a per-hardware basis in hw/bsp/{NAME}/family.c (eg, for the RP2040).

In Flipper-development-land, short of adding this to the firmware, apps only have access to a subset of wrapped hal functions; hence, the analogous SPI API funcs I would need to write for use in a Flipper App would be a bit different than using the low-level HAL of the STM32WB55RG itself. Given this, what would be the most appropriate way for me to implement the SPI API funcs for your max3421e code? Any way to write it that would conform to the existing approach of tinyusb for different HW, or best to cannibalize just the src/portable/analog/max3421/hcd_max3421.c file and implement those SPI API funcs locally in my project using the Flipper's API? (and more broadly, am I asking the right questions here, or misunderstanding the proper approach of using tinyusb?)

[zacharyweiss]

e.g., would it be appropriate to create a "sub-board" file in hw/bsp/stm32wb/ that specifies use of the wrapped / Flipper-Zero-Firmware-specific functions, a la BOARD=STM32WB_FLIPPERZERO?