- Enable CAN FD frame support and BRS.
- Optimize the message RAM usage per FDCAN instance.
- Document the usage and different sections of the Message RAM.
The original code used a independent state with regards to the interrupt.
During heavy bus error conditions the internal state could become
out-of-sync with the interrupts.
Further explanation: during the development of an application using CAN
communication, a interrupt-run-away was found in some situations. It was
found that the error interrupt triggered (Warning, Passive or Bus-Off, all
triggered it) the run-away. The only recovery was a reset.
Two problems were found:
- the error interrupt is enabled but not cleared in the interrupt routine;
- an internal variable 'State' that was used to track the message received
state (empty, new, full, overflow) that was not directly related to
interrupt that indicated the state.
In this commit these issues are fixed by adding more values for the
interrupt reason (warning, passive, bus off) and clearing the error
interrupts, and making the internal state directly dependent on the
interrupt state for received messages.
Furthermore, introducing the FIFO1 in the CAN receive stage, another issue
existed. Even if the messages are received into the FIFO1 (by selecting
message filtering for FIFO0 and FIFO1), the interrupt firing was indicating
FIFO0 Rx. The configuration of the interrupts for this is now also fixed.
The CAN peripheral has 2 interrupt lines going into the NVIC controller.
The assignment of the interrupt reasons to these 2 interrupt lines was
missing. Now the reception of FIFO1 messages triggers the second interrupt
line. Other interrupts (Rx FIFO0 and bus error) are assigned to the first
interrupt line.
Tested on a Nucleo-G474, and also checked the HAL function to work with the
H7 family.
The new fdcan.c file provides the low-level C interface to the FDCAN
peripheral, and pyb_can.c is updated to support both traditional CAN and
FDCAN, depending on the MCU being compiled for.
