Stefan Waldschmidt
Test the thread switching time by implementing semaphore ping-pong between two threads.
Measure thread switching time by implementing semaphore ping-pong between two threads
This mbed program starts two threads with realtime-priority. Each of them is waiting for the other to give its semaphore and gives the other thread's semaphore as a reaction. Once started, this algorithm results in fast thread switches, enforced by the semaphores.
To allow measurement, one thread sets a GPIO output, while to other one clears it.
Measurements are performed on a NUCLEO-F767ZI board https://os.mbed.com/platforms/ST-Nucleo-F767ZI/.
mbed-os-5.12.3
Measured gpio_out output frequency, whitch contains actually two thread switches:
- 6.5 - 7.0 usec (154 kHz - 143 kHz)
Diff: main.cpp
- Revision:
- 0:ea879e5f3ce5
--- /dev/null Thu Jan 01 00:00:00 1970 +0000
+++ b/main.cpp Sat May 11 13:58:02 2019 +0000
@@ -0,0 +1,50 @@
+/*
+ Test thread switching time using semaphore ping-pong
+
+ Hardware: NUCLEO-F767ZI
+ Libraries:
+ mbed-os-5.12.3
+ Measured gpio_out output frequency,
+ which contains actually two thread switches:
+ 6.5 - 7.0 usec (154 kHz - 143 kHz)
+*/
+
+#include "mbed.h"
+
+Semaphore semaphore_on(0);
+Semaphore semaphore_off(0);
+
+DigitalOut gpio_out(PC_8);
+
+void run_on()
+{
+ while (true) {
+ semaphore_on.wait();
+ gpio_out = 1;
+ semaphore_off.release();
+ }
+}
+
+void run_off()
+{
+ while (true) {
+ semaphore_off.wait();
+ gpio_out = 0;
+ semaphore_on.release();
+ }
+}
+
+int main()
+{
+ Thread *thread_on = new Thread(osPriorityRealtime);
+ Thread *thread_off = new Thread(osPriorityRealtime);
+
+ thread_on->start(run_on);
+ thread_off->start(run_off);
+
+ semaphore_on.release();
+
+ while (true) {
+ wait(0.1); // 100 ns
+ }
+}