MDK-ARM Keil, MDK-ARM Datasheet - Page 34

• Manufacturer Part Number: MDK-ARM
• Description: KIT REALVIEW MCU DEVELOPMENT
• Manufacturer: Keil
• Type: Compiler and IDEr

Specifications of MDK-ARM

• For Use With/related Products: ARM MCUs
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

34
Using Semaphores
Although semaphores have a simple set of OS calls, they have a wide range of
synchronizing applications. This makes them perhaps the most challenging
RTOS objects to understand. In this section, we will look at the most common
uses of semaphores. Some are taken from “The Little Book Of Semaphores” by
Allen B. Downy, and may be freely downloaded from the URL given in the
bibliography at the end of this book.
Signaling
Synchronizing the execution of two tasks is the simplest use of a semaphore:
In this case, the semaphore is used to ensure that the code in FuncA() is executed
before the code in FuncB().
Multiplex
A multiplex semaphore limits the number of tasks that can access a critical
section of code. For example, routines that access memory resources and can
support a limited number of calls.
os_sem Multiplex;
void task1 (void) __task
}
os_sem semB;
__task void task1 (void)
}
os_sem_init (Multiplex, 5);
while (1)
}
os_sem_init (semB, 0);
while (1)
}
os_sem_wait (Multiplex, 0xFFFF);
ProcessBuffer ();
os_sem_send (Multiplex);
os_sem_send (semB);
FuncA();
{
{
{
{
__task void task2 (void)
}
while (1)
}
os_sem_wait (semB, 0xFFFF);
FuncB();
Chapter 2. Developing With an RTOS
{
{