events: Added equeue platform timing tests

Tests the timer/semaphores at a lower level than the event queue,
which removes a layer of concerns from issues in the rtos timing.

TESTS/events/timing/main.cpp

@@ -0,0 +1,122 @@
+#include "mbed_events.h"
+#include "mbed.h"
+#include "rtos.h"
+#include "greentea-client/test_env.h"
+#include "unity.h"
+#include "utest.h"
+#include <cstdlib>
+#include <cmath>
+
+using namespace utest::v1;
+
+
+// Test delay
+#ifndef TEST_EVENTS_TIMING_TIME
+#define TEST_EVENTS_TIMING_TIME 20000
+#endif
+
+#ifndef TEST_EVENTS_TIMING_MEAN
+#define TEST_EVENTS_TIMING_MEAN 25
+#endif
+
+#ifndef M_PI
+#define M_PI 3.14159265358979323846264338327950288
+#endif
+
+// Random number generation to skew timing values
+float gauss(float mu, float sigma) {
+    float x = (float)rand() / ((float)RAND_MAX+1);
+    float y = (float)rand() / ((float)RAND_MAX+1);
+    float x2pi = x*2.0*M_PI;
+    float g2rad = sqrt(-2.0 * log(1.0-y));
+    float z = cos(x2pi) * g2rad;
+    return mu + z*sigma;
+}
+
+float chisq(float sigma) {
+    return pow(gauss(0, sqrt(sigma)), 2);
+}
+
+
+Timer timer;
+DigitalOut led(LED1);
+
+equeue_sema_t sema;
+
+// Timer timing test
+void timer_timing_test() {
+    timer.reset();
+    timer.start();
+    int prev = timer.read_us();
+
+    while (prev < TEST_EVENTS_TIMING_TIME*1000) {
+        int next = timer.read_us();
+        if (next < prev) {
+            printf("backwards drift %d -> %d (%08x -> %08x)\r\n",
+                prev, next, prev, next);
+        }
+        TEST_ASSERT(next >= prev);
+        prev = next;
+    }
+}
+
+// equeue tick timing test
+void tick_timing_test() {
+    unsigned start = equeue_tick();
+    int prev = 0;
+
+    while (prev < TEST_EVENTS_TIMING_TIME) {
+        int next = equeue_tick() - start;
+        if (next < prev) {
+            printf("backwards drift %d -> %d (%08x -> %08x)\r\n",
+                prev, next, prev, next);
+        }
+        TEST_ASSERT(next >= prev);
+        prev = next;
+    }
+}
+
+// equeue semaphore timing test
+void semaphore_timing_test() {
+    srand(0);
+    timer.reset();
+    timer.start();
+
+    int err = equeue_sema_create(&sema);
+    TEST_ASSERT_EQUAL(0, err);
+
+    while (timer.read_ms() < TEST_EVENTS_TIMING_TIME) {
+        int delay = chisq(TEST_EVENTS_TIMING_MEAN);
+
+        int start = timer.read_us();
+        equeue_sema_wait(&sema, delay);
+        int taken = timer.read_us() - start;
+
+        printf("delay %dms => error %dus\r\n", delay, abs(1000*delay - taken));
+        TEST_ASSERT_INT_WITHIN(2000, taken, delay * 1000);
+
+        led = !led;
+    }
+
+    equeue_sema_destroy(&sema);
+}
+
+
+// Test setup
+utest::v1::status_t test_setup(const size_t number_of_cases) {
+    GREENTEA_SETUP((number_of_cases+1)*TEST_EVENTS_TIMING_TIME, "default_auto");
+    return verbose_test_setup_handler(number_of_cases);
+}
+
+const Case cases[] = {
+    Case("Testing accuracy of timer", timer_timing_test),
+    Case("Testing accuracy of equeue tick", tick_timing_test),
+    Case("Testing accuracy of equeue semaphore", semaphore_timing_test),
+};
+
+Specification specification(test_setup, cases);
+
+int main() {
+    return !Harness::run(specification);
+}
+