cgo: add more FreeRTOS compatibility

This commit implements:

  * xTaskCreate
  * vTaskDelay
  * xSemaphoreCreateCounting (partially)
  * xSemaphoreTake
  * xSemaphoreGive
  * xQueueCreate
  * vQueueDelete
  * xQueueReceive
  * xQueueSend
  * uxQueueMessagesWaiting

Author: aykevl

src/compat/freertos/freertos.c

@@ -0,0 +1,6 @@
+#include "freertos/FreeRTOS.h"
+#include "freertos/task.h"
+
+void freertos_callFunction(void (*function)(void *), void *parameter) {
+    function(parameter);
+}

src/compat/freertos/freertos.go

@@ -4,11 +4,14 @@
 package freertos
 
 // #include <freertos/FreeRTOS.h>
+// #include <freertos/queue.h>
 // #include <freertos/semphr.h>
 // #include <freertos/task.h>
+// void freertos_callFunction(void (*function)(void *), void *parameter);
 import "C"
 import (
 	"sync"
+	"time"
 	"unsafe"
 
 	"internal/task"
@@ -19,30 +22,66 @@ func xTaskGetCurrentTaskHandle() C.TaskHandle_t {
 	return C.TaskHandle_t(task.Current())
 }
 
+//export xTaskCreate
+func xTaskCreate(pvTaskCode C.TaskFunction_t, pcName *C.char, usStackDepth uintptr, pvParameters unsafe.Pointer, uxPriority C.UBaseType_t, pxCreatedTask *C.TaskHandle_t) C.BaseType_t {
+	go func() {
+		C.freertos_callFunction(pvTaskCode, pvParameters)
+	}()
+	if pxCreatedTask != nil {
+		// Code expectes there to be *something*.
+		var tcb int
+		*pxCreatedTask = unsafe.Pointer(&tcb)
+	}
+	return 1 // pdPASS
+}
+
+//export vTaskDelay
+func vTaskDelay(xTicksToDelay C.TickType_t) {
+	// The default tick rate appears to be 100Hz (10ms per tick).
+	time.Sleep(time.Duration(xTicksToDelay) * C.portTICK_PERIOD_MS * time.Millisecond)
+}
+
 type Semaphore struct {
 	lock  sync.Mutex // the lock itself
 	task  *task.Task // the task currently locking this semaphore
 	count uint32     // how many times this semaphore is locked
 }
 
+//export xSemaphoreCreateCounting
+func xSemaphoreCreateCounting(uxMaxCount C.UBaseType_t, uxInitialCount C.UBaseType_t) C.SemaphoreHandle_t {
+	if uxMaxCount != 1 || uxInitialCount != 0 {
+		println("TODO: xSemaphoreCreateCounting that's not a mutex")
+		return nil
+	}
+	mutex := Semaphore{}
+	return C.SemaphoreHandle_t(&mutex)
+}
+
 //export xSemaphoreCreateRecursiveMutex
 func xSemaphoreCreateRecursiveMutex() C.SemaphoreHandle_t {
 	var mutex Semaphore
-	return (C.SemaphoreHandle_t)(unsafe.Pointer(&mutex))
+	return (C.SemaphoreHandle_t)(&mutex)
 }
 
 //export vSemaphoreDelete
 func vSemaphoreDelete(xSemaphore C.SemaphoreHandle_t) {
-	mutex := (*Semaphore)(unsafe.Pointer(xSemaphore))
+	mutex := (*Semaphore)(xSemaphore)
 	if mutex.task != nil {
 		panic("vSemaphoreDelete: still locked")
 	}
 }
 
+//export xSemaphoreTake
+func xSemaphoreTake(xSemaphore C.QueueHandle_t, xTicksToWait C.TickType_t) C.BaseType_t {
+	mutex := (*Semaphore)(xSemaphore)
+	mutex.lock.Lock()
+	return 1 // pdTRUE
+}
+
 //export xSemaphoreTakeRecursive
 func xSemaphoreTakeRecursive(xMutex C.SemaphoreHandle_t, xTicksToWait C.TickType_t) C.BaseType_t {
 	// TODO: implement xTickToWait, or at least when xTicksToWait equals 0.
-	mutex := (*Semaphore)(unsafe.Pointer(xMutex))
+	mutex := (*Semaphore)(xMutex)
 	if mutex.task == task.Current() {
 		// Already locked.
 		mutex.count++
@@ -54,9 +93,16 @@ func xSemaphoreTakeRecursive(xMutex C.SemaphoreHandle_t, xTicksToWait C.TickType
 	return 1 // pdTRUE
 }
 
+//export xSemaphoreGive
+func xSemaphoreGive(xSemaphore C.QueueHandle_t) C.BaseType_t {
+	mutex := (*Semaphore)(xSemaphore)
+	mutex.lock.Unlock()
+	return 1 // pdTRUE
+}
+
 //export xSemaphoreGiveRecursive
 func xSemaphoreGiveRecursive(xMutex C.SemaphoreHandle_t) C.BaseType_t {
-	mutex := (*Semaphore)(unsafe.Pointer(xMutex))
+	mutex := (*Semaphore)(xMutex)
 	if mutex.task == task.Current() {
 		// Already locked.
 		mutex.count--
@@ -67,3 +113,44 @@ func xSemaphoreGiveRecursive(xMutex C.SemaphoreHandle_t) C.BaseType_t {
 	}
 	panic("xSemaphoreGiveRecursive: not locked by this task")
 }
+
+//export xQueueCreate
+func xQueueCreate(uxQueueLength C.UBaseType_t, uxItemSize C.UBaseType_t) C.QueueHandle_t {
+	return chanMakeUnsafePointer(uintptr(uxItemSize), uintptr(uxQueueLength))
+}
+
+//export vQueueDelete
+func vQueueDelete(xQueue C.QueueHandle_t) {
+	// TODO: close the channel
+}
+
+//export xQueueReceive
+func xQueueReceive(xQueue C.QueueHandle_t, pvBuffer unsafe.Pointer, xTicksToWait C.TickType_t) C.BaseType_t {
+	// Note: xTicksToWait is ignored.
+	chanRecvUnsafePointer(xQueue, pvBuffer)
+	return 1 // pdTRUE
+}
+
+//export xQueueSend
+func xQueueSend(xQueue C.QueueHandle_t, pvBuffer unsafe.Pointer, xTicksToWait C.TickType_t) C.BaseType_t {
+	// Note: xTicksToWait is ignored.
+	chanSendUnsafePointer(xQueue, pvBuffer)
+	return 1 // pdTRUE
+}
+
+//export uxQueueMessagesWaiting
+func uxQueueMessagesWaiting(xQueue C.QueueHandle_t) C.UBaseType_t {
+	return C.UBaseType_t(chanLenUnsafePointer(xQueue))
+}
+
+//go:linkname chanMakeUnsafePointer runtime.chanMakeUnsafePointer
+func chanMakeUnsafePointer(elementSize uintptr, bufSize uintptr) unsafe.Pointer
+
+//go:linkname chanLenUnsafePointer runtime.chanLenUnsafePointer
+func chanLenUnsafePointer(ch unsafe.Pointer) int
+
+//go:linkname chanSendUnsafePointer runtime.chanSendUnsafePointer
+func chanSendUnsafePointer(ch, value unsafe.Pointer)
+
+//go:linkname chanRecvUnsafePointer runtime.chanRecvUnsafePointer
+func chanRecvUnsafePointer(ch, value unsafe.Pointer)

src/compat/freertos/include/freertos/FreeRTOS.h

@@ -6,4 +6,6 @@ typedef uint32_t     TickType_t;
 typedef int          BaseType_t;
 typedef unsigned int UBaseType_t;
 
-#define portMAX_DELAY (TickType_t)0xffffffffUL
+#define portMAX_DELAY        (TickType_t)0xffffffffUL
+#define portTICK_PERIOD_MS   (10)
+#define configMAX_PRIORITIES (25)

src/compat/freertos/include/freertos/queue.h

@@ -1,3 +1,10 @@
 #pragma once
 
-typedef struct QueueDefinition * QueueHandle_t;
+typedef void * QueueHandle_t;
+
+QueueHandle_t xQueueCreate(UBaseType_t uxQueueLength, UBaseType_t uxItemSize);
+void vQueueDelete(QueueHandle_t xQueue);
+
+BaseType_t xQueueReceive(QueueHandle_t xQueue, void *pvBuffer, TickType_t xTicksToWait);
+BaseType_t xQueueSend(QueueHandle_t xQueue, void *pvBuffer, TickType_t xTicksToWait);
+UBaseType_t uxQueueMessagesWaiting(QueueHandle_t xQueue);

src/compat/freertos/include/freertos/semphr.h

@@ -1,12 +1,17 @@
 #pragma once
 
 // Note: in FreeRTOS, SemaphoreHandle_t is an alias for QueueHandle_t.
-typedef struct SemaphoreDefinition * SemaphoreHandle_t;
+typedef void * SemaphoreHandle_t;
 
+SemaphoreHandle_t xSemaphoreCreateCounting(UBaseType_t uxMaxCount, UBaseType_t uxInitialCount);
 SemaphoreHandle_t xSemaphoreCreateRecursiveMutex(void);
 
 void vSemaphoreDelete(SemaphoreHandle_t xSemaphore);
 
 // Note: these two functions are macros in FreeRTOS.
 BaseType_t xSemaphoreTakeRecursive(SemaphoreHandle_t xMutex, TickType_t xTicksToWait);
 BaseType_t xSemaphoreGiveRecursive(SemaphoreHandle_t xMutex);
+
+// Note: these functions are macros in FreeRTOS.
+BaseType_t xSemaphoreTake(QueueHandle_t xSemaphore, TickType_t xTicksToWait);
+BaseType_t xSemaphoreGive(QueueHandle_t xSemaphore);

src/compat/freertos/include/freertos/task.h

@@ -1,5 +1,10 @@
 #pragma once
 
 typedef void * TaskHandle_t;
+typedef void (*TaskFunction_t)(void *);
 
 TaskHandle_t xTaskGetCurrentTaskHandle(void);
+
+BaseType_t xTaskCreate(TaskFunction_t pvTaskCode, const char * const pcName, uintptr_t usStackDepth, void *pvParameters, UBaseType_t uxPriority, TaskHandle_t *pxCreatedTask);
+
+void vTaskDelay(const TickType_t xTicksToDelay);

src/runtime/chan.go

@@ -127,6 +127,10 @@ type channel struct {
 	buf         unsafe.Pointer // pointer to first element of buffer
 }
 
+func chanMakeUnsafePointer(elementSize, bufSize uintptr) unsafe.Pointer {
+	return unsafe.Pointer(chanMake(elementSize, bufSize))
+}
+
 // chanMake creates a new channel with the given element size and buffer length in number of elements.
 // This is a compiler intrinsic.
 func chanMake(elementSize uintptr, bufSize uintptr) *channel {
@@ -495,6 +499,11 @@ func chanSend(ch *channel, value unsafe.Pointer, blockedlist *channelBlockedList
 	sender.Ptr = nil
 }
 
+func chanSendUnsafePointer(ch, value unsafe.Pointer) {
+	var blockedlist channelBlockedList
+	chanSend((*channel)(ch), value, &blockedlist)
+}
+
 // chanRecv receives a single value over a channel.
 // It blocks if there is no available value to recieve.
 // The recieved value is copied into the value pointer.
@@ -532,6 +541,11 @@ func chanRecv(ch *channel, value unsafe.Pointer, blockedlist *channelBlockedList
 	return ok
 }
 
+func chanRecvUnsafePointer(ch, value unsafe.Pointer) {
+	var blockedlist channelBlockedList
+	chanRecv((*channel)(ch), value, &blockedlist)
+}
+
 // chanClose closes the given channel. If this channel has a receiver or is
 // empty, it closes the channel. Else, it panics.
 func chanClose(ch *channel) {