tom dunigan / Mbed 2 deprecated k64f_rtcisr

measure RTC crystal freqeuncy against MCU crystal

Dependencies:   mbed

This program uses the RTC 1-second interrupt to capture the Timer microsecond value to estimate the error in the RTC's 32KHz crystal. (the K64F MCU's crystal could be in error as well, though mine was within 20 ppm). This program measured the error at about 250 ppm, well out of the 20ppm spec for the RTC crystal???

Files at this revision

API Documentation at this revision

Revision 0:b30b04f4a2aa, committed 2015-10-27

Comitter:
manitou
Date:
Tue Oct 27 21:07:11 2015 +0000
Commit message:
first cut

Changed in this revision

main.cpp Show annotated file Show diff for this revision Revisions of this file
mbed.bld Show annotated file Show diff for this revision Revisions of this file 
diff -r 000000000000 -r b30b04f4a2aa main.cpp
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/main.cpp	Tue Oct 27 21:07:11 2015 +0000
@@ -0,0 +1,35 @@
+// k64f rtcisr
+// seconds interrupt from RTC compare micros() to check RTC frequency
+#include "mbed.h"
+
+#define micros tmr.read_us
+
+DigitalOut led(LED_RED);
+Timer tmr;
+
+volatile static unsigned long ticks,us;
+static unsigned long us0=0;
+
+extern "C" void RTC_Seconds_IRQHandler() {
+    if (us0 == 0) us0 = micros();
+      else {
+        ticks++;
+        us = micros() - us0;
+    }
+    led = !led; // toggle led
+}
+
+int main(){
+    int ppm, tprev=0;
+
+    tmr.start();   // for micros
+    time(NULL);  // start RTC
+    RTC_IER = 0x10 ;    //TSIE enable seconds interrupt
+    NVIC_EnableIRQ(RTC_Seconds_IRQn);
+    while (true) {
+        ppm = 1000000*ticks - us;
+        ppm = 1.e6 * ppm/ (float)us;
+        printf("%d %d %f %d\n",ticks,ticks-tprev,us*1.e-6,ppm);
+        wait(2.0);
+    }
+}
\ No newline at end of file

diff -r 000000000000 -r b30b04f4a2aa mbed.bld
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/mbed.bld	Tue Oct 27 21:07:11 2015 +0000
@@ -0,0 +1,1 @@
+http://mbed.org/users/mbed_official/code/mbed/builds/34e6b704fe68
\ No newline at end of file