diff --git a/wiringPi/test/wiringpi_test9_pwm.c b/wiringPi/test/wiringpi_test9_pwm.c
new file mode 100644
index 0000000..ca0b349
--- /dev/null
+++ b/wiringPi/test/wiringpi_test9_pwm.c
@@ -0,0 +1,159 @@
+// WiringPi test program: PWM test
+// Compile: gcc -Wall wiringpi_test9_pwm.c -o wiringpi_test9_pwm -lwiringPi
+
+#include "wpi_test.h"
+#include <string.h>
+#include <errno.h>
+#include <unistd.h>
+#include <sys/time.h>
+#include <time.h>
+#include <stdint.h>
+
+
+int PWM0 = 12;
+int FREQIN = 6;
+
+volatile int gCounter = 0;
+
+//Interrupt Service Routine for FREQIN
+void ISR_FREQIN(void) {
+	gCounter++;
+}
+
+double MeasureAndCheckFreq(const char* msg, double expect_freq) {
+	double fFrequency;
+	clock_t CPUClockBegin, CPUClockEnd;
+	int CountBegin, CountEnd;
+	double CPUClockInterval, CountInterval;
+	double elapsed_time, CPULoad;
+  uint64_t tbegin, tend;
+  int SleepMs = 1200;
+
+  CPUClockBegin = clock();
+	tbegin = piMicros64();
+  CountBegin = gCounter;
+  delay(SleepMs);
+  CountEnd = gCounter;
+  CPUClockEnd = clock();
+	tend = piMicros64();
+
+  elapsed_time = (double)(tend-tbegin)/1.0e6;
+  CountInterval = CountEnd - CountBegin;
+	CPUClockInterval = CPUClockEnd - CPUClockBegin;
+  CPULoad = CPUClockInterval*100.0 / CLOCKS_PER_SEC / elapsed_time;
+  fFrequency = CountInterval / elapsed_time / 1000;
+
+  printf("Interval:  time: %.6f sec (CPU: %3.1f %%), count: %g  -> frequency: %.3f kHz\n", 
+    elapsed_time, CPULoad, CountInterval, fFrequency);
+
+  CheckSameDouble("Wait for freq. meas.", elapsed_time, SleepMs/1000.0, 0.1); //100ms tolerance. maybe problematic on high freq/cpu load 
+  CheckSameDouble(msg, fFrequency, expect_freq, expect_freq*2/100); //2% tolerance
+
+  return fFrequency;
+}
+
+
+int tests_pwmc[7] = {1456, 1000,  512,  100, 2000, 3000, 4000};
+int tests_duty[7] = { 512,  768,  682,  922,  256,  341,  102};
+int tests_pwmr[10]= { 100,  512, 1024, 1456, 2000, 3000, 5000, 10000, 15000, 20000};
+
+int main (void) {
+
+	int major, minor;
+  char msg[255];
+
+	wiringPiVersion(&major, &minor);
+
+	printf("WiringPi GPIO test program 9 (using PWM@GPIO%d (output) and GPIO%d (input))\n", PWM0, FREQIN);
+	printf(" pwm0 irq time\n");
+
+	printf("\nPWM/ISR test (WiringPi %d.%d)\n", major, minor);
+
+	wiringPiSetupGpio() ;
+
+	int rev, mem, maker, overVolted, RaspberryPiModel;
+	piBoardId(&RaspberryPiModel, &rev, &mem, &maker, &overVolted);
+	CheckNotSame("Model: ", RaspberryPiModel, -1);
+
+	if (!piBoard40Pin()) {
+		PWM0 = 18;
+		FREQIN = 17;
+	}
+// INT_EDGE_BOTH, INT_EDGE_FALLING, INT_EDGE_RISING only one ISR per input
+	int result = wiringPiISR(FREQIN, INT_EDGE_RISING, &ISR_FREQIN);
+  CheckSame("Register ISR", result, 0);
+   if (result < 0) {
+		printf("Unable to setup ISR for GPIO %d (%s)\n\n", 
+		  FREQIN, strerror(errno));
+    return UnitTestState();
+	} 
+
+  int Pi4 = 0;
+  switch(RaspberryPiModel) {
+    case PI_MODEL_4B:
+    case PI_MODEL_400:
+    case PI_MODEL_CM4:
+    case PI_MODEL_CM4S:   
+      Pi4 = 1;
+      break;
+    case PI_MODEL_5:
+      return UnitTestState();  //not supported so far
+  }
+
+  printf("\nPWM0 BAL mode:\n");
+  printf("==============\n");
+
+	pinMode(PWM0, PWM_OUTPUT);  //pwmr=1024, pwmc=32
+  const int pmw = 512;
+  int pmwr = 1024;
+  pwmWrite(PWM0, pmw);  //50% Duty
+  //MeasureAndCheckFreq("50\% Duty (default)", 300.000);   //FAIL , freq (pwmc=32) to high for irq count
+
+  for (int c_duty=0, c_duty_end = sizeof(tests_duty)/sizeof(tests_duty[0]); c_duty<c_duty_end; c_duty++) {
+
+    double tests_duty_corr;
+    if (tests_duty[c_duty]>(pmwr/2)) {
+      tests_duty_corr = pmwr-tests_duty[c_duty];  
+    } else {
+      tests_duty_corr = tests_duty[c_duty];
+    }
+
+    double duty_fact = tests_duty_corr/(double)pmwr;
+    printf("\n%d/%d set duty %d/%d\n",c_duty+1, c_duty_end, tests_duty[c_duty], pmwr);
+    pwmWrite(PWM0, tests_duty[c_duty]);
+
+    for (int c_pwmc=0, end = sizeof(tests_pwmc)/sizeof(tests_pwmc[0]); c_pwmc<end; c_pwmc++) {
+      if (Pi4 && tests_pwmc[c_pwmc]>1456) {
+        printf("* Set Clock (pwmc) %d not possible on BCM2711 system (OSC 54 MHz), ignore\n", tests_pwmc[c_pwmc]);
+        continue;
+      }
+      pwmSetClock(tests_pwmc[c_pwmc]);
+      delay(250);
+      double freq = 19200.0/tests_pwmc[c_pwmc]*duty_fact;
+      sprintf(msg, "Set Clock (pwmc) %d, %d%% duty", tests_pwmc[c_pwmc], tests_duty[c_duty]*100/pmwr);
+      MeasureAndCheckFreq(msg, freq);
+    }
+
+  }
+
+  delay(250);
+  pwmSetMode(PWM_MODE_MS) ;
+  printf("\nPWM0 MS mode:\n");
+  printf("==============\n");
+
+  int pwmc = 10; 
+  pwmSetClock(pwmc);
+  delay(2500);
+
+  for (int c_pmwr=0, c_pmwr_end = sizeof(tests_pwmr)/sizeof(tests_pwmr[0]); c_pmwr<c_pmwr_end; c_pmwr++) {
+    pwmWrite(PWM0, tests_pwmr[c_pmwr]/2); 
+    pwmSetRange(tests_pwmr[c_pmwr]) ;
+    delay(250);
+    double freq = 19200.0/(double)pwmc/(double)tests_pwmr[c_pmwr];
+    sprintf(msg, "Set range (pwmr) %d", tests_pwmr[c_pmwr]);
+    MeasureAndCheckFreq(msg, freq);
+  }
+
+
+	return UnitTestState();
+}
diff --git a/wiringPi/test/wpi_test.h b/wiringPi/test/wpi_test.h
index d29b363..5bded06 100644
--- a/wiringPi/test/wpi_test.h
+++ b/wiringPi/test/wpi_test.h
@@ -105,6 +105,16 @@ void CheckSameFloat(const char* msg, float value, float expect) {
 }
 
 
+void CheckSameDouble(const char* msg, double value, double expect, double epsilon) {
+    if (fabs(value-expect)<epsilon) {
+        printf("%35s (%.3f==%.3f) -> %spassed%s \n", msg, value, expect, COLORGRN, COLORDEF);
+    } else {
+        printf("%35s (%.3f<>%.3f) -> %sfailed%s \n" , msg, value, expect, COLORRED, COLORDEF);
+        globalError=1;
+    }
+}
+
+
 int UnitTestState() {
     printf("\n\nUNIT TEST STATE: ");
     if (globalError) {