Added rudimentary FreeRTOS implementation

Mostly based on the *FromISR set of functions to be compatible with
critical sections/interrupt contexts.

equeue_tick  = xTaskGetTickCountFromISR
equeue_mutex = taskENTER_CRITICAL_FROM_ISR
equeue_sema  = xSemaphoreCreateBinaryStatic

equeue_freertos.c

@@ -0,0 +1,61 @@
+/*
+ * Implementation for the mbed library
+ * https://github.com/mbedmicro/mbed
+ *
+ * Copyright (c) 2016 Christopher Haster
+ * Distributed under the MIT license
+ */
+#include "equeue_tick.h"
+#include "equeue_sema.h"
+#include "equeue_mutex.h"
+
+#if defined(EQUEUE_PLATFORM_FREERTOS)
+
+#include "task.h"
+
+
+// Ticker operations
+unsigned equeue_tick(void) {
+    return xTaskGetTickCountFromISR() * portTICK_PERIOD_MS;
+}
+
+
+// Mutex operations
+int equeue_mutex_create(equeue_mutex_t *m) { return 0; }
+void equeue_mutex_destroy(equeue_mutex_t *m) { }
+
+void equeue_mutex_lock(equeue_mutex_t *m) {
+    *m = taskENTER_CRITICAL_FROM_ISR();
+}
+
+void equeue_mutex_unlock(equeue_mutex_t *m) {
+    taskEXIT_CRITICAL_FROM_ISR(*m);
+}
+
+
+// Semaphore operations
+int equeue_sema_create(equeue_sema_t *s) {
+    s->handle = xSemaphoreCreateBinaryStatic(&s->buffer);
+    return s->handle ? 0 : -1;
+}
+
+void equeue_sema_destroy(equeue_sema_t *s) {
+    vSemaphoreDelete(s->handle);
+}
+
+void equeue_sema_signal(equeue_sema_t *s) {
+    xSemaphoreGiveFromISR(s->handle, NULL);
+}
+
+bool equeue_sema_wait(equeue_sema_t *s, int ms) {
+    if (ms < 0) {
+        ms = portMAX_DELAY;
+    } else {
+        ms = ms / portTICK_PERIOD_MS;
+    }
+
+    return xSemaphoreTake(s->handle, ms);
+}
+
+
+#endif

equeue_mutex.h

@@ -27,6 +27,9 @@ typedef pthread_mutex_t equeue_mutex_t;
 typedef CRITICAL_SECTION equeue_mutex_t;
 #elif defined(__MBED__)
 typedef unsigned equeue_mutex_t;
+#elif defined(EQUEUE_PLATFORM_FREERTOS)
+#include "FreeRTOS.h"
+typedef UBaseType_t equeue_mutex_t;
 #endif
 
 

equeue_sema.h

@@ -39,6 +39,13 @@ typedef HANDLE equeue_sema_t;
 typedef unsigned equeue_sema_t[8];
 #elif defined(__MBED__)
 typedef volatile int equeue_sema_t;
+#elif defined(EQUEUE_PLATFORM_FREERTOS)
+#include "FreeRTOS.h"
+#include "semphr.h"
+typedef struct equeue_sema {
+    SemaphoreHandle_t handle;
+    StaticSemaphore_t buffer;
+} equeue_sema_t;
 #endif