Queues Example

Queue Message Passing

Run producer and consumer tasks that exchange timestamped messages through a bounded queue.

Board LPCXpresso51U68 EVB OM40005

Status Verified

Download lpc51u68_cleveros_queue_demo_main.c

Run It

Use these commands from the COS workspace when the board and serial adapter are attached.

make -C firmware/lpc51u68_cleveros_queue_demo clean allmake -C firmware/lpc51u68_cleveros_queue_demo flashmake -C firmware/lpc51u68_cleveros_queue_demo verify flashpython3 tools/uart_viewer.py --device <serial-device> --baud 9600

What To Look For

Producer sends two messages per second.
Consumer receives every 400 ms.
Queue depth and message age are visible in serial output.

Download Code From This Website Open Repository

#include <stdint.h>

#include "cos_lpc51u68_bsp.h"
#include "cos_lpc51u68_rtos.h"

#define QUEUE_CAPACITY 4u

typedef struct {
    uint32_t id;
    uint32_t produced_ms;
} queue_message_t;

static queue_message_t g_queue[QUEUE_CAPACITY];
static uint32_t g_queue_head;
static uint32_t g_queue_tail;
static uint32_t g_queue_count;

static uint32_t queue_try_send(queue_message_t message, uint32_t *depth)
{
    uint32_t sent = 0u;

    rtos_critical_enter();
    if (g_queue_count < QUEUE_CAPACITY) {
        g_queue[g_queue_tail] = message;
        g_queue_tail = (g_queue_tail + 1u) & (QUEUE_CAPACITY - 1u);
        g_queue_count++;
        sent = 1u;
    }
    *depth = g_queue_count;
    rtos_critical_exit();

    return sent;
}

static uint32_t queue_try_recv(queue_message_t *message, uint32_t *depth)
{
    uint32_t received = 0u;

    rtos_critical_enter();
    if (g_queue_count != 0u) {
        *message = g_queue[g_queue_head];
        g_queue_head = (g_queue_head + 1u) & (QUEUE_CAPACITY - 1u);
        g_queue_count--;
        received = 1u;
    }
    *depth = g_queue_count;
    rtos_critical_exit();

    return received;
}

static void task_producer(void)
{
    uint32_t message_id = 0u;

    for (;;) {
        queue_message_t message = {
            .id = message_id++,
            .produced_ms = rtos_tick_ms(),
        };
        uint32_t depth = 0u;
        while (queue_try_send(message, &depth) == 0u) {
            rtos_delay_ticks(100u);
        }
        rtos_delay_ticks(500u);
    }
}

static void task_consumer(void)
{
    for (;;) {
        queue_message_t message = {0u, 0u};
        uint32_t depth = 0u;

        if (queue_try_recv(&message, &depth) != 0u) {
            cos_lpc51u68_led_step_t step = (cos_lpc51u68_led_step_t)(message.id & 0x3u);
            rtos_set_led_step(step);
            cos_lpc51u68_uart0_puts("queue cons tick ");
            cos_lpc51u68_uart0_put_hex32(rtos_tick_ms());
            cos_lpc51u68_uart0_puts(" msg ");
            cos_lpc51u68_uart0_put_hex32(message.id);
            cos_lpc51u68_uart0_puts(" depth ");
            cos_lpc51u68_uart0_put_hex32(depth);
            cos_lpc51u68_uart0_puts("\r\n");
        }

        rtos_delay_ticks(400u);
    }
}