OSAL的消息机制触发事件流程
定时器触发事件一般为程序内部触发，若外部触发事件，可以用系统消息触发，以按键触发为例。
在初始化时候，InitBoard()中，注册了按键回调函数
HalKeyConfig( OnboardKeyIntEnable, OnBoard_KeyCallback);
该函数中注册按键回调函数到pHalKeyProcessFunction，并启动定时器事件，ID为HAL层ID，事件为按键事件，调用HalKeyPoll(),启动按键轮询，等待按键触发。
halProcessKeyInterrupt()通过HAL_ISR_FUNCTION()注册到OSAL的中断机制中，此部分代码没有公开，可能是底层按键触发中断，然后调用halProcessKeyInterrupt()上报事件，HalKeyPoll()中调用初始化时候注册的按键回调函数(pHalKeyProcessFunction) ()进行处理;
在回调函数中，调用OnBoard_SendKeys()函数发送系统消息，消息结构如下
typedef struct
{
void *next;
uint16 len;
uint8 dest_id;
} osal_msg_hdr_t;
typedef struct
{
uint8 event;
uint8 status;
} osal_event_hdr_t;
typedef struct
{
osal_event_hdr_t hdr;
uint8 state;
uint8 keys;
} keyChange_t;
回调函数OnBoard_SendKeys()原型如下：
1 /********************************************************************* 2 3 * @fn OnBoard_SendKeys 4 5 * 6 7 * @brief Send "Key Pressed" message to application. 8 9 * 10 11 * @param keys - keys that were pressed 12 13 * state - shifted 14 15 * 16 17 * @return status 18 19 *********************************************************************/ 20 21 uint8 OnBoard_SendKeys( uint8 keys, uint8 state ) 22 23 { 24 25 keyChange_t *msgPtr; 26 27 if ( registeredKeysTaskID != NO_TASK_ID ) 28 29 { 30 31 // Send the address to the task 32 33 msgPtr = (keyChange_t *)osal_msg_allocate( sizeof(keyChange_t) ); 34 35 if ( msgPtr ) 36 37 { 38 39 msgPtr->hdr.event = KEY_CHANGE; 40 41 msgPtr->state = state; 42 43 msgPtr->keys = keys; 44 45 46 osal_msg_send( registeredKeysTaskID, (uint8 *)msgPtr ); 47 48 } 49 50 return ( SUCCESS ); 51 52 } 53 54 else 55 56 return ( FAILURE ); 57 58 }
在OnBoard_SendKeys()函数中，调用osal_msg_allocate()函数申请一块内存,
1 /********************************************************************* 2 3 * @fn osal_msg_allocate 4 5 * 6 7 * @brief 8 9 * 10 11 * This function is called by a task to allocate a message buffer 12 13 * into which the task will encode the particular message it wishes 14 15 * to send. This common buffer scheme is used to strictly limit the 16 17 * creation of message buffers within the system due to RAM size 18 19 * limitations on the microprocessor. Note that all message buffers 20 21 * are a fixed size (at least initially). The parameter len is kept 22 23 * in case a message pool with varying fixed message sizes is later 24 25 * created (for example, a pool of message buffers of size LARGE, 26 27 * MEDIUM and SMALL could be maintained and allocated based on request 28 29 * from the tasks). 30 31 * 32 33 * 34 35 * @param uint8 len - wanted buffer length 36 37 * 38 39 * 40 41 * @return pointer to allocated buffer or NULL if allocation failed. 42 43 */ 44 45 uint8 * osal_msg_allocate( uint16 len ) 46 47 { 48 49 osal_msg_hdr_t *hdr; 50 51 52 if ( len == 0 ) 53 54 return ( NULL ); 55 56 57 58 hdr = (osal_msg_hdr_t *) osal_mem_alloc( (short)(len + sizeof( osal_msg_hdr_t )) ); 59 60 if ( hdr ) 61 62 { 63 64 hdr->next = NULL; 65 66 hdr->len = len; 67 68 hdr->dest_id = TASK_NO_TASK; 69 70 return ( (uint8 *) (hdr + 1) ); 71 72 } 73 74 else 75 76 return ( NULL ); 77 78 }
其内存布局如下：
申请成功后，返回值为keyChange_t部分的首地址，因此在随后的消息检查，填充等操作中会有结构体指针减一的操作。
消息创建完成后，调用osal_msg_send()将消息发送出去，该函数调用osal_msg_enqueue_push()，将消息发送至OSAL消息链表，并调用osal_set_event( destination_task, SYS_EVENT_MSG );向目标任务发送一个系统消息事件，在主循环中调用目标任务的回调函数，进入系统消息处理分支接收并解析处理消息。
