[jpieper]

Here "allocation" is all fixed size things pulled from a fixed size buffer at startup. Technically malloc is compiled in the firmware, but it isn't used for anything but some C++ runtime initialization confirmed with debugger breakpoints. The only dynamic use of memory is the call stack, which has only fixed size local variables and limited depth recursion.

Similarly, "interrupts" may not mean what you are thinking. The highest priority interrupt is one attached to the PWM timer that operates the primary control loop that operates in interrupt context. As of a few months ago this is slightly more complicated to accommodate some "soft" quadrature decoding, but the principle is still the same that all motor control is performed in an interrupt context and nearly nothing else is.

Everything else, like CAN communication, is performed in a polling manner in the "main" loop.

[zbrozek]

Are you out of timers? IIRC the STM32 series typically has timer peripherals that can be configured as encoder inputs.

[jpieper]

No, but out of pins connected to timers with the appropriate capabilities.