Summary

I have been writing a bunch of articles about implementing PSoC FreeRTOS so, this morning I was reading the FreeRTOS manual (yes I am one of those…) and I noticed a section in the API guide that I hadn’t see before… Task Notifications.  Every task in the FreeRTOS has a built in 32-bit integer notification value.  This value is super light weight and can be used like a task specific counting semaphore, or a signaling bit mask, or binary semaphore.  The API includes:

• xTaskNotifyGive()
• vTaskNotifyGiveFromISR()
• ulTaskNotifyTake()
• xTaskNotify()
• xTaskNotifyAndQuery()
• xTaskNotifyAndQueryFromISR()
• xTaskNotifyFromISR()
• xTaskNotifyWait()
• xTaskNotifyStateClear()

It seems like this API is good for the situations when your Semaphore has a specific task target in mind.  I thought that this would be a perfect scheme to have a PSoC FreeRTOS UART ISR signal the UART Handling task that there is data available to do something with.

Setup the PSoC FreeRTOS Project

I start this process by making a copy of “1-BlinkingLED” (which already has all of the FreeRTOS stuff in it) and naming it “9-TaskNotify”.  Then I add a UART to the schematic and name it “UART”

I attach the UART to the right pins on the CY8CKIT-044 kit.

Next I turn on the interrupt which will be called when there is data in the receive FIFO.

PSoC FreeRTOS UART Code

Now that the schematic is all configured I update my firmware.  The function “uartHandler” is called when there is data in the UART RX FIFO.  It turns of the interrupts for the UART (which I will turn back on after I have cleared the data in the input buffer), clears the interrupt  (so that it will stop pending) and then sends the notification to the UART_Task.

The UART Task just registers the handler… then while(1)’s until the end of time.  It waits for a notification, then reads data out of the RX fifo and puts out,  then re-enables the interrupts.

CY_ISR(uartHandler)
{
    BaseType_t xHigherPriorityTaskWoken;

    // disable the interrupt
    UART_SetRxInterruptMode(0);
    vTaskNotifyGiveFromISR(uartTaskHandle,&xHigherPriorityTaskWoken);
    portYIELD_FROM_ISR( xHigherPriorityTaskWoken );
}

void UART_Task( void *arg)
{
    (void)arg;
    char c;
    UART_Start();
    UART_SetCustomInterruptHandler(uartHandler);
    while(1)
    {
        ulTaskNotifyTake(pdTRUE,portMAX_DELAY);
        while(UART_SpiUartGetRxBufferSize())
        {
            c = UART_UartGetChar();
            UART_UartPutChar(c);
        }
        // clear & re-enable the interrupt
        UART_ClearRxInterruptSource(UART_INTR_RX_NOT_EMPTY);
        UART_SetRxInterruptMode(UART_INTR_RX_NOT_EMPTY);
    }
}