hobbielektronika
In this example three threads are competing for two resources. The number of free resources is managed in a semaphore while the indiviual resource accesses are protected by 1-1 mutex. The RGB LED shows the waitings state of tasks accessing no resource.
Revision 0:15e98ba559c1, committed 2016-02-10
- Comitter:
- icserny
- Date:
- Wed Feb 10 12:43:09 2016 +0000
- Commit message:
- First version
Changed in this revision
diff -r 000000000000 -r 15e98ba559c1 main.cpp
--- /dev/null Thu Jan 01 00:00:00 1970 +0000
+++ b/main.cpp Wed Feb 10 12:43:09 2016 +0000
@@ -0,0 +1,64 @@
+/** 10_rtos_semaphore
+ * In this example three threads are competing for two
+ * resources. The number of free resources is managed in a semaphore
+ * while the indiviual resource accesses are protected by 1-1 mutex.
+ * The RGB LED shows the waitings state of tasks accessing no resource.
+ *
+ * Hardware requirements:
+ * - FRDM-KL25Z board
+ */
+
+#include "mbed.h"
+#include "rtos.h"
+
+Semaphore sem(2); //manges two tokens
+Mutex m1, m2; //two mutexes for two resources
+Mutex stdio_mutex; //Control shared access to printf
+DigitalOut led1(LED1); //Red LED
+DigitalOut led2(LED2); //Green LED
+DigitalOut led3(LED3); //Blue LED
+DigitalOut ledarray[]= {led1,led2,led3}; //Just needed for indexing the individual objects...
+Timer mytime;
+
+void notify(int tid, int res) {
+ stdio_mutex.lock();
+ if(res > 0) {
+ printf("Task %d: acquired << resource %d. at %8.1f\n\r", tid, res, mytime.read());
+ } else {
+ printf("Task %d: released >> resource %d. at %8.1f\n\r", tid, -res, mytime.read());
+ }
+ stdio_mutex.unlock();
+}
+
+void mythread(void const* args) {
+ while (true) {
+ Thread::wait(500+rand()%500);
+ ledarray[(int)args-1]=0; //LEDx on
+ sem.wait(); //Wait for token
+ if(m1.trylock()) { //Try to lock mutex #1
+ ledarray[(int)args-1]=1; //LEDx off
+ notify((int)args,1);
+ Thread::wait(1000+rand()%500);
+ notify((int)args,-1);
+ m1.unlock();
+ } else {
+ m2.lock(); //Wait for mutex #2
+ ledarray[(int)args-1]=1; //LEDx off
+ notify((int)args,2);
+ Thread::wait(1000+rand()%500);
+ notify((int)args,-2);
+ m2.unlock();
+ }
+ sem.release(); //Release token
+ }
+}
+
+int main (void) {
+ led1 = 1;
+ led2 = 1;
+ led3 = 1; //Switch off all LEDs
+ mytime.start(); //Start timer
+ Thread t2(mythread,(void *)2U); //Define and run thread2
+ Thread t3(mythread,(void *)3U); //Define and run thread3
+ mythread((void const*)1U); //Run thread1
+}
diff -r 000000000000 -r 15e98ba559c1 mbed-rtos.lib --- /dev/null Thu Jan 01 00:00:00 1970 +0000 +++ b/mbed-rtos.lib Wed Feb 10 12:43:09 2016 +0000 @@ -0,0 +1,1 @@ +http://mbed.org/users/mbed_official/code/mbed-rtos/#3d9d2b8b8f17
diff -r 000000000000 -r 15e98ba559c1 mbed.bld --- /dev/null Thu Jan 01 00:00:00 1970 +0000 +++ b/mbed.bld Wed Feb 10 12:43:09 2016 +0000 @@ -0,0 +1,1 @@ +http://mbed.org/users/mbed_official/code/mbed/builds/f141b2784e32 \ No newline at end of file