CAN System

Overview

The CanSystem implements the ICanSystem interface for the NUCLEO-G474RE using the STM32G474RE’s FDCAN1 peripheral. It manages a single FdCanTransceiver (CAN_0), participates in the lifecycle as a SingleContextLifecycleComponent running in the TASK_CAN context, and provides the extern "C" ISR trampolines. It is registered as an etl::singleton so the ISR handlers can reach the instance without global variables.

Hardware Configuration

FDCAN1 uses PA11 (RX) and PA12 (TX), alternate function AF9. An external CAN transceiver is required to drive the bus. Bit timing at 170 MHz kernel clock: prescaler 20 (8.5 MHz time quantum), 17 TQ per bit (1 sync + 14 seg1 + 2 seg2), giving 500 kbit/s with a sample point of 88.2 %.

Lifecycle

init() only signals transitionDone() - the peripheral is untouched until run(), which:

1. Enables the CanRxRunnable.

2. Initializes and opens the FdCanTransceiver (FDCAN1 register setup, accept-all filter, normal mode).

3. Enables the RX FIFO 0 interrupt and configures the NVIC:

   FDCAN1->IE  = FDCAN_IE_RF0NE;
   FDCAN1->ILS = 0U;
   FDCAN1->ILE = FDCAN_ILE_EINT0;
   
   NVIC_SetPriority(FDCAN1_IT0_IRQn, FDCAN_IRQ_PRIORITY);
   NVIC_SetPriority(FDCAN1_IT1_IRQn, FDCAN_IRQ_PRIORITY);
   NVIC_ClearPendingIRQ(FDCAN1_IT0_IRQn);
   NVIC_ClearPendingIRQ(FDCAN1_IT1_IRQn);
   NVIC_EnableIRQ(FDCAN1_IT0_IRQn);
   NVIC_EnableIRQ(FDCAN1_IT1_IRQn);
   

   Under FreeRTOS, FDCAN_IRQ_PRIORITY must stay numerically greater than or equal to configLIBRARY_MAX_SYSCALL_INTERRUPT_PRIORITY so the ISRs can safely use FromISR APIs.

4. Schedules a periodic 50 ms timer that runs the CanTxRunnable.

shutdown() closes and shuts down the transceiver and disables the RX runnable.

Interrupt Handling

With ILS = 0 all FDCAN1 interrupt sources are routed to interrupt line 0 (only EINT0 is enabled), so FDCAN1_IT0_IRQHandler handles both RX and TX events while FDCAN1_IT1_IRQHandler / call_can_isr_TX() are empty. call_can_isr_RX() reads FDCAN1->IR once and:

• on RF0N, reads pending frames from the hardware FIFO into the software queue under lock (FdCanTransceiver::receiveInterrupt) and, if frames were received, dispatches the CanRxRunnable into the TASK_CAN context;

• on TC, forwards the TX-complete event to FdCanTransceiver::transmitInterrupt.

The CanRxRunnable calls receiveTask(), which drains the software queue and notifies the registered frame listeners. The CanTxRunnable calls FdCanTransceiver::pollTxCallback(CAN_0), which invokes the sent listener of completed transmissions; the 50 ms timer guarantees this poll runs even when a dispatch from the ISR is dropped by the async dedup logic.