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Hires timestamp

Question asked by Ole Asbjorn Fadum on Apr 10, 2015

Hi,

 

We are using K64F12, KDS-2.0, KSDK-1.1.0 in a measurement system. When performing measurements we must have a hi-res timer to time-stamp measurements.

I've used the fsl_hwtimer as timer, but it seems to load the system terribly!!! I must have a timer with resolution 8us, and I've made this test:

 

1. The CPU is running at 20.9 MHz

2. The fsl_hwtimer is set to a period of 1000 us

 

I've connected a logic-analyzer to the serial-port and times how long it will take to print 256 x 'a' (115200 baud)

 

A: When fsl_timer running at 1000us, the output is done in 81ms

B: When fsl_timer is changed to 10us, the output is done in 1787.9 ms !!!

 

It seems that the only source for fsl_timer is PIT.

I don't understand why the change of the timer frequency should slow down the system this much. I thought that how fast the clock was running should not be

noticable for the sw at all?

 

What should I do to get my hi-resolution sample-timer, and NOT slow down my sw to a limping run?

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