CooCox CoOS User's Guide

Code 2 The use of the semaphore
void myTaskA(void* pdata)
{
..........
semID = CoCreateSem(0,1,EVENT_SORT_TYPE_FIFO);
CoPendSem(semID,0);
..........
}
void myTaskB(void* pdata)
{
......
CoPostSem(semID);
......
}
void myISR(void)
{
CoEnterISR();
......
isr_PostSem(semID);
CoExitISR();
}
5.1.2 Mutexes
Mutexes have solved the "mutually exclusion" problem in CooCox CoOS. It
forbids multiple tasks to enter the critical code section at the same time.
Therefore, only one task can enter it at any time.
In CooCox CoOS, the mutex section has also considered the issue of
priority inversion. CooCox CoOS has solved this issue by the method of priority
inheritance.
Priority inversion refers to that the high-priority task is waiting for the
low-priority task to release resources, at the same time the low-priority task is
waiting for the middle priority task’s.
There are two classical methods to prevent the inversion at present:
1) The priority inheritance strategy: The task which is possessing the critical
section inherits the highest priority of all the tasks that request for this critical
section. When the task exits from the critical section, it will restore to its original
priority.
2) The ceiling priority strategy: Upgrade the priority of the task which
requests a certain resource to the highest priority of all the tasks that be likely
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