Event Handling

✅ Open the stm32-code/standalone-app/src/bin/standalone-rtic-event.rs file.

Below the idle function you’ll see a #[task] handler, a function. This task is bound to the USART1 interrupt signal and will be executed, function-call style, every time the interrupt signal is raised by the hardware.

Add these two lines to the #[init] function:

board.usart1.configure(bsp::APB2_PERIPH_CLK_HZ);
board.usart1.rx_interrupt_enable(true);

This will configure UART and cause a UART interrupt to fire whenever the UART has data in its buffer.

✅ Run the modified standalone-rtic-event application. Then connect Serial Terminal to your board (as you did in the Green and Yellow exercise) and send some bytes to the UART.

Note that all tasks will be prioritized over the idle function so the execution of idle will be interrupted (paused) by the usart1_handler task. When the usart1_handler task finishes (returns) the execution of the idle will be resumed. This will become more obvious in the next section.

What do you observe? Will usart1_handler ever stop being called?

✅ Try this: add an infinite loop to the end of init so that it never returns. Now run the program and send some bytes to the UART. What behavior do you observe? How would you explain this behavior? (hint: look at the rtic-expansion.rs file: under what conditions is the init function executed?)