How to handle timeout in FreeRTOS - wake up task from interrupt before vTaskDelay expires?

Question

Can I wake up task before vTaskDelay expires?

I have code like this:

In the task (hnd_uart_task) code:

transmit_frame();
vTaskDelay(100);  // task should wait 100 ticks or be woken up by uart ISR
parse_response();

UART Interrupt:

// if byte was received
BaseType_t xYieldRequired = xTaskResumeFromISR(hnd_uart_task);
portYIELD_FROM_ISR(xYieldRequired);

Answer 1

Instead of using vTaskDelay(), you can use task notifications with timeout.

USART Interrupt:

// if byte was received
BaseType_t xHigherPriorityTaskWoken = pdFALSE;
vTaskNotifyGiveFromISR(hnd_uart_task, &xHigherPriorityTaskWoken);
portYIELD_FROM_ISR(xHigherPriorityTaskWoken);

Task Code:

transmit_frame();
ulTaskNotifyTake(pdTRUE, 100);
parse_response();

ulTaskNotifyTake(pdTRUE, 100) returns when a task notification is received from the ISR, or when 100 tick timeout period elapses.

But as @Jacek Ślimok pointed out, a byte-by-byte parsing may not be good idea. The exact method depends on the protocol used. But in general, you set up your DMA or interrupts to fill a reception buffer with incoming bytes. For example, when parsing Modbus frames, you can use idle line detection hardware interrupt and give notification to a task which parses the RX buffer.