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FreeRTOS Symmetric Multiprocessing (SMP) is a version of the RTOS that can schedule tasks across multiple controller cores.
It's a very simple example - on purpose. With a few lines of code, we can make jobs run on either Pico ARM core. |
Download and install FreeRTOS
Clone FreeRTOS if you don't have it yet. The SMP part is recently added to FreeRTOS proper. The version that comes with Pico C SDK 1.5 doesn't have it yet.
git clone https://github.com/FreeRTOS/FreeRTOS.git --recurse-submodules
We'll tell our project later where it can find the RTOS.
The Double Blinky example
Goal: run two FreeRTOS tasks. Both on a different core.
The base for my code is the CORTEX_M0+_RP2040 SMP blinky demo code. You can find it in the FreeRTOS\FreeRTOS\Demo\ThirdParty\Community-Supported-Demos\CORTEX_M0+_RP2040\Standard_smp folder.
I added support for controlling what core to run a task on (instead of letting the scheduler decide).
FreeRTOSConfig.h is set up to use 2 cores, and to allow "core affinity"
#define configNUMBER_OF_CORES 2 #define configTICK_CORE 0 #define configRUN_MULTIPLE_PRIORITIES 0 // ... /* RP2040 specific */ #define configSUPPORT_PICO_SYNC_INTEROP 1 #define configSUPPORT_PICO_TIME_INTEROP 1 // ... /* SMP Related config. */ #define configUSE_PASSIVE_IDLE_HOOK 0 #define portSUPPORT_SMP 1 #define configUSE_CORE_AFFINITY 1
The LED blink task is virtually the same as the one from the demo. I used the parameter to tell which LED to blink
static void prvLedTask(void *pvParameters) {
TickType_t xNextWakeTime;
xNextWakeTime = xTaskGetTickCount();
for( ;; ) {
vTaskDelayUntil( &xNextWakeTime, mainLED_FREQUENCY_MS );
gpio_xor_mask(1u << (uint32_t)pvParameters);
}
}
The main code schedules two of those tasks. Tells each of them to blink a different LED, and run on a different core:
TaskHandle_t xHandle;
xTaskCreate(prvLedTask, "LED", configMINIMAL_STACK_SIZE, (void *)mainTASK_LED1, mainLED_TASK_PRIORITY, &(xHandle) );
// Define the core affinity mask such that this task can only run on core 0
vTaskCoreAffinitySet(xHandle, (1 << 0));
xTaskCreate(prvLedTask, "LED2", configMINIMAL_STACK_SIZE, (void *)mainTASK_LED2, mainLED_TASK_PRIORITY, &(xHandle) );
// Define the core affinity mask such that this task can only run on core 1
vTaskCoreAffinitySet(xHandle, (1 << 1));
vTaskStartScheduler();
Result:
"Hey, my code can't find (the right) FreeRTOS on my disk?"
The project includes a file in the CMake script that 'll help you to find the RTOS: FreeRTOS_Kernel_import.cmake.
Define a variable FREERTOS_KERNEL_PATH that points to the install (in my case, C:/Users/jancu/Documents/git/git_freertos/FreeRTOS/FreeRTOS/Source).
You can set it as an OS variable, or use the functionality of your IDE. Here's how I did that in VSCode:
Enjoy the FreeRTOS SMP double blinky. The download below includes the .uf2 file, that can be copied directly onto the Pico. LEDs will flash after you flash the firmware.
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