ChibiOS Free Embedded RTOS

Yes, using the provided callbacks is what I meant, but I'm assuming they're called in a ISR context, right? So I'm not able to use the synchronous message API, and doing SPI from an interrupt context (concurrently with a thread) sounds not so great

I'm building an USB frontend to some kind of (SPI) chipset and I'm planning to implement some non standard (control) requests through EP0 to expose some chipset registers ; keeping EP1 for bulk data. Currently, from my understanding, the USB requests hook is supposed to call usbSetupTransfer() macro ...