Chapter 7.1 - 消息邮箱管理
Created by : Mr Dk.
2019 / 11 / 20 11:01
Nanjing, Jiangsu, China
7.1.1 概述
邮箱是一种通信机制，使任务或中断服务向另一个任务发送一个 指针型变量，该指针指向包含消息的数据结构。使用邮箱的目的：
- 通知一个事件的发生：邮箱初始化为 NULL
- 作二值信号量用：邮箱初始化为一个非 NULL 指针
邮箱只能接受和发送一个消息，邮箱为满时，新消息丢失。邮箱相关的函数可以全部被剪裁。
7.1.2 建立消息邮箱 - OSMboxCreate() 函数
建立并初始化一个消息邮箱，可以选择带一个参数，指向消息的指针，作为邮箱中的初始消息（当然也可以初始化空邮箱）。
原理：
- 从空闲 ECB 链表中找到一个空闲 ECB
- 调整
OSEventFreeList指针指向下一个空闲 ECB - 初始化为消息邮箱 ECB，存入邮箱消息初始值
- 对等待任务列表进行初始化
- 返回 ECB 指针
/*
*********************************************************************************************************
* CREATE A MESSAGE MAILBOX
*
* Description: This function creates a message mailbox if free event control blocks are available.
*
* Arguments : pmsg is a pointer to a message that you wish to deposit in the mailbox. If
* you set this value to the NULL pointer (i.e. (void *)0) then the mailbox
* will be considered empty.
*
* Returns : != (OS_EVENT *)0 is a pointer to the event control clock (OS_EVENT) associated with the
* created mailbox
* == (OS_EVENT *)0 if no event control blocks were available
*********************************************************************************************************
*/
OS_EVENT *OSMboxCreate (void *pmsg)
{
OS_EVENT *pevent;
#if OS_CRITICAL_METHOD == 3u /* Allocate storage for CPU status register */
OS_CPU_SR cpu_sr = 0u;
#endif
#ifdef OS_SAFETY_CRITICAL_IEC61508
if (OSSafetyCriticalStartFlag == OS_TRUE) {
OS_SAFETY_CRITICAL_EXCEPTION();
}
#endif
if (OSIntNesting > 0u) { /* See if called from ISR ... */
return ((OS_EVENT *)0); /* ... can't CREATE from an ISR */
}
OS_ENTER_CRITICAL();
pevent = OSEventFreeList; /* Get next free event control block */
if (OSEventFreeList != (OS_EVENT *)0) { /* See if pool of free ECB pool was empty */
OSEventFreeList = (OS_EVENT *)OSEventFreeList->OSEventPtr;
}
OS_EXIT_CRITICAL();
if (pevent != (OS_EVENT *)0) {
pevent->OSEventType = OS_EVENT_TYPE_MBOX;
pevent->OSEventCnt = 0u;
pevent->OSEventPtr = pmsg; /* Deposit message in event control block */
#if OS_EVENT_NAME_EN > 0u
pevent->OSEventName = (INT8U *)(void *)"?";
#endif
OS_EventWaitListInit(pevent);
}
return (pevent); /* Return pointer to event control block */
}
删除消息邮箱 - OSMboxDel() 函数
删除消息邮箱。还是有两个条件选项：
OS_DEL_NO_PEND：没有任何任务等待该邮箱的消息时，才删除邮箱OS_DEL_ALWAYS：不管有没有任务在等待消息，都删除邮箱
如果删除失败，可以通过错误码查询原因。
原理：将 ECB 置为未使用状态，并归还给空闲链表。
/*
*********************************************************************************************************
* DELETE A MAIBOX
*
* Description: This function deletes a mailbox and readies all tasks pending on the mailbox.
*
* Arguments : pevent is a pointer to the event control block associated with the desired
* mailbox.
*
* opt determines delete options as follows:
* opt == OS_DEL_NO_PEND Delete the mailbox ONLY if no task pending
* opt == OS_DEL_ALWAYS Deletes the mailbox even if tasks are waiting.
* In this case, all the tasks pending will be readied.
*
* perr is a pointer to an error code that can contain one of the following values:
* OS_ERR_NONE The call was successful and the mailbox was deleted
* OS_ERR_DEL_ISR If you attempted to delete the mailbox from an ISR
* OS_ERR_INVALID_OPT An invalid option was specified
* OS_ERR_TASK_WAITING One or more tasks were waiting on the mailbox
* OS_ERR_EVENT_TYPE If you didn't pass a pointer to a mailbox
* OS_ERR_PEVENT_NULL If 'pevent' is a NULL pointer.
*
* Returns : pevent upon error
* (OS_EVENT *)0 if the mailbox was successfully deleted.
*
* Note(s) : 1) This function must be used with care. Tasks that would normally expect the presence of
* the mailbox MUST check the return code of OSMboxPend().
* 2) OSMboxAccept() callers will not know that the intended mailbox has been deleted!
* 3) This call can potentially disable interrupts for a long time. The interrupt disable
* time is directly proportional to the number of tasks waiting on the mailbox.
* 4) Because ALL tasks pending on the mailbox will be readied, you MUST be careful in
* applications where the mailbox is used for mutual exclusion because the resource(s)
* will no longer be guarded by the mailbox.
*********************************************************************************************************
*/
#if OS_MBOX_DEL_EN > 0u
OS_EVENT *OSMboxDel (OS_EVENT *pevent,
INT8U opt,
INT8U *perr)
{
BOOLEAN tasks_waiting;
OS_EVENT *pevent_return;
#if OS_CRITICAL_METHOD == 3u /* Allocate storage for CPU status register */
OS_CPU_SR cpu_sr = 0u;
#endif
#ifdef OS_SAFETY_CRITICAL
if (perr == (INT8U *)0) {
OS_SAFETY_CRITICAL_EXCEPTION();
}
#endif
#if OS_ARG_CHK_EN > 0u
if (pevent == (OS_EVENT *)0) { /* Validate 'pevent' */
*perr = OS_ERR_PEVENT_NULL;
return (pevent);
}
#endif
if (pevent->OSEventType != OS_EVENT_TYPE_MBOX) { /* Validate event block type */
*perr = OS_ERR_EVENT_TYPE;
return (pevent);
}
if (OSIntNesting > 0u) { /* See if called from ISR ... */
*perr = OS_ERR_DEL_ISR; /* ... can't DELETE from an ISR */
return (pevent);
}
OS_ENTER_CRITICAL();
if (pevent->OSEventGrp != 0u) { /* See if any tasks waiting on mailbox */
tasks_waiting = OS_TRUE; /* Yes */
} else {
tasks_waiting = OS_FALSE; /* No */
}
switch (opt) {
case OS_DEL_NO_PEND: /* Delete mailbox only if no task waiting */
if (tasks_waiting == OS_FALSE) {
#if OS_EVENT_NAME_EN > 0u
pevent->OSEventName = (INT8U *)(void *)"?";
#endif
pevent->OSEventType = OS_EVENT_TYPE_UNUSED;
pevent->OSEventPtr = OSEventFreeList; /* Return Event Control Block to free list */
pevent->OSEventCnt = 0u;
OSEventFreeList = pevent; /* Get next free event control block */
OS_EXIT_CRITICAL();
*perr = OS_ERR_NONE;
pevent_return = (OS_EVENT *)0; /* Mailbox has been deleted */
} else {
OS_EXIT_CRITICAL();
*perr = OS_ERR_TASK_WAITING;
pevent_return = pevent;
}
break;
case OS_DEL_ALWAYS: /* Always delete the mailbox */
while (pevent->OSEventGrp != 0u) { /* Ready ALL tasks waiting for mailbox */
(void)OS_EventTaskRdy(pevent, (void *)0, OS_STAT_MBOX, OS_STAT_PEND_OK);
}
#if OS_EVENT_NAME_EN > 0u
pevent->OSEventName = (INT8U *)(void *)"?";
#endif
pevent->OSEventType = OS_EVENT_TYPE_UNUSED;
pevent->OSEventPtr = OSEventFreeList; /* Return Event Control Block to free list */
pevent->OSEventCnt = 0u;
OSEventFreeList = pevent; /* Get next free event control block */
OS_EXIT_CRITICAL();
if (tasks_waiting == OS_TRUE) { /* Reschedule only if task(s) were waiting */
OS_Sched(); /* Find highest priority task ready to run */
}
*perr = OS_ERR_NONE;
pevent_return = (OS_EVENT *)0; /* Mailbox has been deleted */
break;
default:
OS_EXIT_CRITICAL();
*perr = OS_ERR_INVALID_OPT;
pevent_return = pevent;
break;
}
return (pevent_return);
}
#endif
7.1.4 等待邮箱中的信息 - OSMboxPend() 函数
用于等待邮箱中的信息：
- 如果邮箱中已有信息，那么将消息返回调用者，并清除消息
- 如果邮箱中没有信息，则挂起当前任务，直到有信息来或超时
- 如果多个任务等待同一个消息，则交给优先级最高的任务并转为就绪
- 由
OSTaskSuspend()函数挂起的任务也可以接受消息，但维持挂起状态不变
原理：从 ECB 中读取 OSEventPtr
- 若不为空，则直接返回消息指针
- 若为空，则任务挂起等待消息
/*
*********************************************************************************************************
* PEND ON MAILBOX FOR A MESSAGE
*
* Description: This function waits for a message to be sent to a mailbox
*
* Arguments : pevent is a pointer to the event control block associated with the desired mailbox
*
* timeout is an optional timeout period (in clock ticks). If non-zero, your task will
* wait for a message to arrive at the mailbox up to the amount of time
* specified by this argument. If you specify 0, however, your task will wait
* forever at the specified mailbox or, until a message arrives.
*
* perr is a pointer to where an error message will be deposited. Possible error
* messages are:
*
* OS_ERR_NONE The call was successful and your task received a
* message.
* OS_ERR_TIMEOUT A message was not received within the specified 'timeout'.
* OS_ERR_PEND_ABORT The wait on the mailbox was aborted.
* OS_ERR_EVENT_TYPE Invalid event type
* OS_ERR_PEND_ISR If you called this function from an ISR and the result
* would lead to a suspension.
* OS_ERR_PEVENT_NULL If 'pevent' is a NULL pointer
* OS_ERR_PEND_LOCKED If you called this function when the scheduler is locked
*
* Returns : != (void *)0 is a pointer to the message received
* == (void *)0 if no message was received or,
* if 'pevent' is a NULL pointer or,
* if you didn't pass the proper pointer to the event control block.
*********************************************************************************************************
*/
/*$PAGE*/
void *OSMboxPend (OS_EVENT *pevent,
INT32U timeout,
INT8U *perr)
{
void *pmsg;
#if OS_CRITICAL_METHOD == 3u /* Allocate storage for CPU status register */
OS_CPU_SR cpu_sr = 0u;
#endif
#ifdef OS_SAFETY_CRITICAL
if (perr == (INT8U *)0) {
OS_SAFETY_CRITICAL_EXCEPTION();
}
#endif
#if OS_ARG_CHK_EN > 0u
if (pevent == (OS_EVENT *)0) { /* Validate 'pevent' */
*perr = OS_ERR_PEVENT_NULL;
return ((void *)0);
}
#endif
if (pevent->OSEventType != OS_EVENT_TYPE_MBOX) { /* Validate event block type */
*perr = OS_ERR_EVENT_TYPE;
return ((void *)0);
}
if (OSIntNesting > 0u) { /* See if called from ISR ... */
*perr = OS_ERR_PEND_ISR; /* ... can't PEND from an ISR */
return ((void *)0);
}
if (OSLockNesting > 0u) { /* See if called with scheduler locked ... */
*perr = OS_ERR_PEND_LOCKED; /* ... can't PEND when locked */
return ((void *)0);
}
OS_ENTER_CRITICAL();
pmsg = pevent->OSEventPtr;
if (pmsg != (void *)0) { /* See if there is already a message */
pevent->OSEventPtr = (void *)0; /* Clear the mailbox */
OS_EXIT_CRITICAL();
*perr = OS_ERR_NONE;
return (pmsg); /* Return the message received (or NULL) */
}
OSTCBCur->OSTCBStat |= OS_STAT_MBOX; /* Message not available, task will pend */
OSTCBCur->OSTCBStatPend = OS_STAT_PEND_OK;
OSTCBCur->OSTCBDly = timeout; /* Load timeout in TCB */
OS_EventTaskWait(pevent); /* Suspend task until event or timeout occurs */
OS_EXIT_CRITICAL();
OS_Sched(); /* Find next highest priority task ready to run */
OS_ENTER_CRITICAL();
switch (OSTCBCur->OSTCBStatPend) { /* See if we timed-out or aborted */
case OS_STAT_PEND_OK:
pmsg = OSTCBCur->OSTCBMsg;
*perr = OS_ERR_NONE;
break;
case OS_STAT_PEND_ABORT:
pmsg = (void *)0;
*perr = OS_ERR_PEND_ABORT; /* Indicate that we aborted */
break;
case OS_STAT_PEND_TO:
default:
OS_EventTaskRemove(OSTCBCur, pevent);
pmsg = (void *)0;
*perr = OS_ERR_TIMEOUT; /* Indicate that we didn't get event within TO */
break;
}
OSTCBCur->OSTCBStat = OS_STAT_RDY; /* Set task status to ready */
OSTCBCur->OSTCBStatPend = OS_STAT_PEND_OK; /* Clear pend status */
OSTCBCur->OSTCBEventPtr = (OS_EVENT *)0; /* Clear event pointers */
#if (OS_EVENT_MULTI_EN > 0u)
OSTCBCur->OSTCBEventMultiPtr = (OS_EVENT **)0;
#endif
OSTCBCur->OSTCBMsg = (void *)0; /* Clear received message */
OS_EXIT_CRITICAL();
return (pmsg); /* Return received message */
}
7.1.5 发出邮箱消息 - OSMboxPost() 函数
- 如果邮箱中已有消息，则立刻返回调用者，并丢弃新消息
- 如果邮箱中没有消息
- 如果有任务在等待消息，则最高优先级任务得到这个消息
- 如果没有任务等待消息，则消息的指针被保存在邮箱中
调用者可以是任务或中断。
原理：
- 检查 ECB 的
OSEventPtr是否为空咯 - 检查 ECB 的等待任务列表检查是否有任务等待消息咯
- 投递消息或丢弃消息咯
/*
*********************************************************************************************************
* POST MESSAGE TO A MAILBOX
*
* Description: This function sends a message to a mailbox
*
* Arguments : pevent is a pointer to the event control block associated with the desired mailbox
*
* pmsg is a pointer to the message to send. You MUST NOT send a NULL pointer.
*
* Returns : OS_ERR_NONE The call was successful and the message was sent
* OS_ERR_MBOX_FULL If the mailbox already contains a message. You can can only send one
* message at a time and thus, the message MUST be consumed before you
* are allowed to send another one.
* OS_ERR_EVENT_TYPE If you are attempting to post to a non mailbox.
* OS_ERR_PEVENT_NULL If 'pevent' is a NULL pointer
* OS_ERR_POST_NULL_PTR If you are attempting to post a NULL pointer
*
* Note(s) : 1) HPT means Highest Priority Task
*********************************************************************************************************
*/
#if OS_MBOX_POST_EN > 0u
INT8U OSMboxPost (OS_EVENT *pevent,
void *pmsg)
{
#if OS_CRITICAL_METHOD == 3u /* Allocate storage for CPU status register */
OS_CPU_SR cpu_sr = 0u;
#endif
#if OS_ARG_CHK_EN > 0u
if (pevent == (OS_EVENT *)0) { /* Validate 'pevent' */
return (OS_ERR_PEVENT_NULL);
}
if (pmsg == (void *)0) { /* Make sure we are not posting a NULL pointer */
return (OS_ERR_POST_NULL_PTR);
}
#endif
if (pevent->OSEventType != OS_EVENT_TYPE_MBOX) { /* Validate event block type */
return (OS_ERR_EVENT_TYPE);
}
OS_ENTER_CRITICAL();
if (pevent->OSEventGrp != 0u) { /* See if any task pending on mailbox */
/* Ready HPT waiting on event */
(void)OS_EventTaskRdy(pevent, pmsg, OS_STAT_MBOX, OS_STAT_PEND_OK);
OS_EXIT_CRITICAL();
OS_Sched(); /* Find highest priority task ready to run */
return (OS_ERR_NONE);
}
if (pevent->OSEventPtr != (void *)0) { /* Make sure mailbox doesn't already have a msg */
OS_EXIT_CRITICAL();
return (OS_ERR_MBOX_FULL);
}
pevent->OSEventPtr = pmsg; /* Place message in mailbox */
OS_EXIT_CRITICAL();
return (OS_ERR_NONE);
}
#endif
7.1.6 发出邮箱消息 - OSMboxPostOpt() 函数
与上个函数的逻辑基本相同。不同的是，如果有任务在等待邮箱里的信息，提供了两种选项对信息进行处理：
OS_POST_OPT_NONE：让最高优先级的任务得到这则消息OS_POST_OPT_BROADCAST：让所有等待消息的任务得到这则消息
原理：
- 检查 ECB 的等待任务列表
- 将所有或最高优先级任务置为就绪
- 如果没有任务正在等待消息，则保存至 ECB 中
/*
*********************************************************************************************************
* POST MESSAGE TO A MAILBOX
*
* Description: This function sends a message to a mailbox
*
* Arguments : pevent is a pointer to the event control block associated with the desired mailbox
*
* pmsg is a pointer to the message to send. You MUST NOT send a NULL pointer.
*
* opt determines the type of POST performed:
* OS_POST_OPT_NONE POST to a single waiting task
* (Identical to OSMboxPost())
* OS_POST_OPT_BROADCAST POST to ALL tasks that are waiting on the mailbox
*
* OS_POST_OPT_NO_SCHED Indicates that the scheduler will NOT be invoked
*
* Returns : OS_ERR_NONE The call was successful and the message was sent
* OS_ERR_MBOX_FULL If the mailbox already contains a message. You can can only send one
* message at a time and thus, the message MUST be consumed before you
* are allowed to send another one.
* OS_ERR_EVENT_TYPE If you are attempting to post to a non mailbox.
* OS_ERR_PEVENT_NULL If 'pevent' is a NULL pointer
* OS_ERR_POST_NULL_PTR If you are attempting to post a NULL pointer
*
* Note(s) : 1) HPT means Highest Priority Task
*
* Warning : Interrupts can be disabled for a long time if you do a 'broadcast'. In fact, the
* interrupt disable time is proportional to the number of tasks waiting on the mailbox.
*********************************************************************************************************
*/
#if OS_MBOX_POST_OPT_EN > 0u
INT8U OSMboxPostOpt (OS_EVENT *pevent,
void *pmsg,
INT8U opt)
{
#if OS_CRITICAL_METHOD == 3u /* Allocate storage for CPU status register */
OS_CPU_SR cpu_sr = 0u;
#endif
#if OS_ARG_CHK_EN > 0u
if (pevent == (OS_EVENT *)0) { /* Validate 'pevent' */
return (OS_ERR_PEVENT_NULL);
}
if (pmsg == (void *)0) { /* Make sure we are not posting a NULL pointer */
return (OS_ERR_POST_NULL_PTR);
}
#endif
if (pevent->OSEventType != OS_EVENT_TYPE_MBOX) { /* Validate event block type */
return (OS_ERR_EVENT_TYPE);
}
OS_ENTER_CRITICAL();
if (pevent->OSEventGrp != 0u) { /* See if any task pending on mailbox */
if ((opt & OS_POST_OPT_BROADCAST) != 0x00u) { /* Do we need to post msg to ALL waiting tasks ? */
while (pevent->OSEventGrp != 0u) { /* Yes, Post to ALL tasks waiting on mailbox */
(void)OS_EventTaskRdy(pevent, pmsg, OS_STAT_MBOX, OS_STAT_PEND_OK);
}
} else { /* No, Post to HPT waiting on mbox */
(void)OS_EventTaskRdy(pevent, pmsg, OS_STAT_MBOX, OS_STAT_PEND_OK);
}
OS_EXIT_CRITICAL();
if ((opt & OS_POST_OPT_NO_SCHED) == 0u) { /* See if scheduler needs to be invoked */
OS_Sched(); /* Find HPT ready to run */
}
return (OS_ERR_NONE);
}
if (pevent->OSEventPtr != (void *)0) { /* Make sure mailbox doesn't already have a msg */
OS_EXIT_CRITICAL();
return (OS_ERR_MBOX_FULL);
}
pevent->OSEventPtr = pmsg; /* Place message in mailbox */
OS_EXIT_CRITICAL();
return (OS_ERR_NONE);
}
#endif
7.1.7 无等待地从邮箱中获取消息 - OSMboxAccept() 函数
查看指定的邮箱中是否有需要的消息，且不挂起任务。调用者可以是任务，也可以是中断。
/*
*********************************************************************************************************
* ACCEPT MESSAGE FROM MAILBOX
*
* Description: This function checks the mailbox to see if a message is available. Unlike OSMboxPend(),
* OSMboxAccept() does not suspend the calling task if a message is not available.
*
* Arguments : pevent is a pointer to the event control block
*
* Returns : != (void *)0 is the message in the mailbox if one is available. The mailbox is cleared
* so the next time OSMboxAccept() is called, the mailbox will be empty.
* == (void *)0 if the mailbox is empty or,
* if 'pevent' is a NULL pointer or,
* if you didn't pass the proper event pointer.
*********************************************************************************************************
*/
#if OS_MBOX_ACCEPT_EN > 0u
void *OSMboxAccept (OS_EVENT *pevent)
{
void *pmsg;
#if OS_CRITICAL_METHOD == 3u /* Allocate storage for CPU status register */
OS_CPU_SR cpu_sr = 0u;
#endif
#if OS_ARG_CHK_EN > 0u
if (pevent == (OS_EVENT *)0) { /* Validate 'pevent' */
return ((void *)0);
}
#endif
if (pevent->OSEventType != OS_EVENT_TYPE_MBOX) { /* Validate event block type */
return ((void *)0);
}
OS_ENTER_CRITICAL();
pmsg = pevent->OSEventPtr;
pevent->OSEventPtr = (void *)0; /* Clear the mailbox */
OS_EXIT_CRITICAL();
return (pmsg); /* Return the message received (or NULL) */
}
#endif
7.1.8 查询邮箱的状态 - OSMboxQuery() 函数
将 ECB 中的邮箱状态复制到一个简单的数据结构 OS_MBOX_DATA 中并返回。无需等待，所以调用者可以是任务也可以是中断。
/*
*********************************************************************************************************
* QUERY A MESSAGE MAILBOX
*
* Description: This function obtains information about a message mailbox.
*
* Arguments : pevent is a pointer to the event control block associated with the desired mailbox
*
* p_mbox_data is a pointer to a structure that will contain information about the message
* mailbox.
*
* Returns : OS_ERR_NONE The call was successful and the message was sent
* OS_ERR_EVENT_TYPE If you are attempting to obtain data from a non mailbox.
* OS_ERR_PEVENT_NULL If 'pevent' is a NULL pointer
* OS_ERR_PDATA_NULL If 'p_mbox_data' is a NULL pointer
*********************************************************************************************************
*/
#if OS_MBOX_QUERY_EN > 0u
INT8U OSMboxQuery (OS_EVENT *pevent,
OS_MBOX_DATA *p_mbox_data)
{
INT8U i;
OS_PRIO *psrc;
OS_PRIO *pdest;
#if OS_CRITICAL_METHOD == 3u /* Allocate storage for CPU status register */
OS_CPU_SR cpu_sr = 0u;
#endif
#if OS_ARG_CHK_EN > 0u
if (pevent == (OS_EVENT *)0) { /* Validate 'pevent' */
return (OS_ERR_PEVENT_NULL);
}
if (p_mbox_data == (OS_MBOX_DATA *)0) { /* Validate 'p_mbox_data' */
return (OS_ERR_PDATA_NULL);
}
#endif
if (pevent->OSEventType != OS_EVENT_TYPE_MBOX) { /* Validate event block type */
return (OS_ERR_EVENT_TYPE);
}
OS_ENTER_CRITICAL();
p_mbox_data->OSEventGrp = pevent->OSEventGrp; /* Copy message mailbox wait list */
psrc = &pevent->OSEventTbl[0];
pdest = &p_mbox_data->OSEventTbl[0];
for (i = 0u; i < OS_EVENT_TBL_SIZE; i++) {
*pdest++ = *psrc++;
}
p_mbox_data->OSMsg = pevent->OSEventPtr; /* Get message from mailbox */
OS_EXIT_CRITICAL();
return (OS_ERR_NONE);
}
#endif /* OS_MBOX_QUERY_EN */
Summary
仔细一想，邮箱和信号量并没有什么卵区别，一个是数，一个是指针罢了。不过邮箱中比较特殊的一点就是，新消息不能覆盖旧消息，而是被丢弃了。