István Cserny / Mbed 2 deprecated Lab08_4semaphores

In this example semaphores are used to ensure the running order of the program threads. Analogous to the relay race.

Dependencies:   mbed mbed-rtos

main.cpp@0:6d3407923be9, 2022-03-17 (annotated)

Committer:
cspista
Date:
Thu Mar 17 12:38:12 2022 +0000
Revision:
0:6d3407923be9
Final version

Who changed what in which revision?

UserRevisionLine numberNew contents of line
cspista 0:6d3407923be9 1 #include "mbed.h"
cspista 0:6d3407923be9 2 #include "rtos.h"
cspista 0:6d3407923be9 3
cspista 0:6d3407923be9 4 Semaphore sem[] = {(1),(0),(0),(0)}; // Set of semaphores
cspista 0:6d3407923be9 5 DigitalOut led[] = {(D13),(D12),(D11),(D10)}; // Set of LEDs
cspista 0:6d3407923be9 6
cspista 0:6d3407923be9 7 void led_thread(void const* args) {
cspista 0:6d3407923be9 8 int i = (int)args-1; // Idx of this task
cspista 0:6d3407923be9 9 int inext = (i+1)%4; // Idx of next task
cspista 0:6d3407923be9 10 while (true) {
cspista 0:6d3407923be9 11 sem[i].wait();
cspista 0:6d3407923be9 12 led[i] = 0; // ith LED on
cspista 0:6d3407923be9 13 Thread::wait(500+rand()%500);
cspista 0:6d3407923be9 14 led[i] = 1; // ith LED off
cspista 0:6d3407923be9 15 sem[inext].release(); // Start new task
cspista 0:6d3407923be9 16 }
cspista 0:6d3407923be9 17 }
cspista 0:6d3407923be9 18
cspista 0:6d3407923be9 19 int main (void) {
cspista 0:6d3407923be9 20 for(int i=0; i<4; i++) {
cspista 0:6d3407923be9 21 led[i]=1; // LEDs off
cspista 0:6d3407923be9 22 }
cspista 0:6d3407923be9 23 Thread t2(led_thread, (void *)2U);
cspista 0:6d3407923be9 24 Thread t3(led_thread, (void *)3U);
cspista 0:6d3407923be9 25 Thread t4(led_thread, (void *)4U);
cspista 0:6d3407923be9 26 led_thread((void *)1U);
cspista 0:6d3407923be9 27 }