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:

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”

PSoC FreeRTOS Schematic

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

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

PSoC UART Configuration


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.

    BaseType_t xHigherPriorityTaskWoken;

    // disable the interrupt
    portYIELD_FROM_ISR( xHigherPriorityTaskWoken );

void UART_Task( void *arg)
    char c;
            c = UART_UartGetChar();
        // clear & re-enable the interrupt

Topic Description
FreeRTOS: A PSoC4 FreeRTOS Port An introduction to making FreeRTOS work on PSoC 4
FreeRTOS PSoC Examples Using multiple tasks in FreeRTOS
FreeRTOS Queue Example Using a queue to communicate between tasks
PSoC 6 FreeRTOS - The First Example Booting FreeRTOS on PSoC 6
FreeRTOS Binary Semaphore An first example of a binary semaphore
FreeRTOS Binary Semaphore (Part 2) Removing polling in the UART Task
FreeRTOS Counting Semaphore An example using a counting semaphore
PSoC FreeRTOS Reading I2C Sensors with a shared I2C Bus
PSoC FreeRTOS Task Notify A light weight scheme to replace Semaphores
PSoC FreeRTOS Task Notification Values A very light weight method to transfer one word of information into a task

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