CmsisRtos2Threads.ino

Runs threads with ARM's CMSIS-RTOS2 API, which works the same on any CMSIS-RTOS2 system. Needs Tools > Operating System > FreeRTOS (SMP) + CMSIS-RTOS2.

The kernel is already running when setup() starts, so osKernelInitialize() and osKernelStart() are not needed. setup() prints the kernel's name (osKernelGetInfo()) and starts two threads with osThreadNew(): one blinks the LED with osDelay(), the other reads A0 exactly every 100 ms (osDelayUntil()) and puts each reading in a message queue. The sampling thread runs at osPriorityAboveNormal, above loop()'s osPriorityNormal, so its timing holds while loop() waits for readings with osMessageQueueGet() and prints them. See CMSIS-RTOS2.

Wiring

A voltage to measure on A0, e.g. a potentiometer wiper (0-3.3 V).

Output

Serial Monitor at 115200 baud; the LED flashes once a second:

Kernel: FreeRTOS V11.1.0+
1203 ms: A0 = 1650 mV
1303 ms: A0 = 1651 mV

// Runs threads with ARM's CMSIS-RTOS2 API, which works the same on any
// CMSIS-RTOS2 system (Keil RTX, Zephyr, other FreeRTOS boards).
// Needs Tools > Operating System > FreeRTOS (SMP) + CMSIS-RTOS2.
//
// The kernel is already running when setup() starts, so osKernelInitialize()
// and osKernelStart() are not needed. setup() starts two threads: one blinks
// the LED, the other reads A0 every 100 ms and puts each reading in a message
// queue. loop() is a thread too: it waits for readings and prints them.
 
#include <cmsis_os2.h>
 
struct Reading {
    uint32_t time_ms;
    uint32_t millivolts;
};
 
osMessageQueueId_t readings;
 
void blinkThread(void*) {
    for (;;) {
        digitalWrite(LED_BUILTIN, HIGH);
        osDelay(100);  // in ticks: 1 tick = 1 ms
        digitalWrite(LED_BUILTIN, LOW);
        osDelay(900);
    }
}
 
void sampleThread(void*) {
    uint32_t wake = osKernelGetTickCount();
    for (;;) {
        const Reading r = {osKernelGetTickCount(), analogReadMillivolts(A0)};
        if (osMessageQueuePut(readings, &r, 0, 0) != osOK) {
            Serial.println("Queue full: reading dropped");
        }
        wake += 100;
        osDelayUntil(wake);  // every 100 ms, however long the work took
    }
}
 
void setup() {
    Serial.begin(115200);
    while (!Serial) {}
    pinMode(LED_BUILTIN, OUTPUT);
 
    char kernel[32];
    osKernelGetInfo(nullptr, kernel, sizeof(kernel));
    Serial.print("Kernel: ");
    Serial.println(kernel);
 
    readings = osMessageQueueNew(20, sizeof(Reading), nullptr);
 
    osThreadAttr_t blink = {};  // unset fields: defaults (osPriorityNormal, like loop())
    blink.name = "blink";
    blink.stack_size = 1024;    // bytes
    osThreadNew(blinkThread, nullptr, &blink);
 
    osThreadAttr_t sample = {};
    sample.name = "sample";
    sample.stack_size = 2048;
    sample.priority = osPriorityAboveNormal;  // above loop(), so its timing holds
    osThreadNew(sampleThread, nullptr, &sample);
}
 
void loop() {
    Reading r;
    if (osMessageQueueGet(readings, &r, nullptr, osWaitForever) == osOK) {  // waits for a reading
        Serial.print(r.time_ms);
        Serial.print(" ms: A0 = ");
        Serial.print(r.millivolts);
        Serial.println(" mV");
    }
}