Initial Release

timer/periodic_sampler/periodic_sampler.c

@@ -0,0 +1,82 @@
+/**
+ * Copyright (c) 2020 Raspberry Pi (Trading) Ltd.
+ *
+ * SPDX-License-Identifier: BSD-3-Clause
+ */
+
+#include <stdio.h>
+#include "pico/stdlib.h"
+#include "pico/util/queue.h"
+
+bool timer_callback(repeating_timer_t *rt);
+
+queue_t sample_fifo;
+
+// using struct as an example, but primitive types can be used too
+typedef struct element {
+    uint value;
+} element_t;
+
+const int FIFO_LENGTH = 32;
+
+int main() {
+    stdio_init_all();
+
+    int hz = 25;
+
+    queue_init(&sample_fifo, sizeof(element_t), FIFO_LENGTH);
+
+    repeating_timer_t timer;
+
+    // negative timeout means exact delay (rather than delay between callbacks)
+    if (!add_repeating_timer_us(-1000000 / hz, timer_callback, NULL, &timer)) {
+        printf("Failed to add timer\n");
+        return 1;
+    }
+
+    // read some blocking
+
+    for (int i = 0; i < 10; i++) {
+        element_t element;
+        queue_remove_blocking(&sample_fifo, &element);
+        printf("Got %d: %d\n", i, element.value);
+    }
+
+    // now retrieve all that are available periodically (simulate polling)
+    for (int i = 0; i < 10; i++) {
+        int count = queue_get_level(&sample_fifo);
+        if (count) {
+            printf("Getting %d, %d:\n", i, count);
+            for (; count > 0; count--) {
+                element_t element;
+                queue_remove_blocking(&sample_fifo, &element);
+                printf("  got %d\n", element.value);
+            }
+        }
+        sleep_us(5000000 / hz); // sleep for 5 times the sampling period
+    }
+
+    cancel_repeating_timer(&timer);
+
+    // drain any remaining
+    element_t element;
+    while (queue_try_remove(&sample_fifo, &element)) {
+        printf("Got remaining %d\n", element.value);
+    }
+
+    queue_free(&sample_fifo);
+    printf("Done\n");
+}
+
+bool timer_callback(repeating_timer_t *rt) {
+    static int v = 100;
+    element_t element = {
+            .value = v
+    };
+    v += 100;
+
+    if (!queue_try_add(&sample_fifo, &element)) {
+        printf("FIFO was full\n");
+    }
+    return true; // keep repeating
+}