FEZ Raptor + SignalCapture

Archive
1

I have been measuring signal by SignalCapture class on my FEZ Raptor. Input signal has 1kHz so i should get values near to 500 micro seconds. But result is like this:

468;
469;
438;
500;
437;
469;
469;
468;
469;
469;
469;
468;
469;
469;
469;
468;
469;
469;
469;


uint[] signal = new uint[2000];
SignalCapture pin = new SignalCapture(G400.PA27, Port.ResistorMode.Disabled, Port.InterruptMode.InterruptEdgeBoth);
pin.ReadTimeout = 5000;
pin.Read(false, signal);
Debug.Print("Done");

I know that G120HDR gave better results, from 499 to 501 micro seconds. In what could be the problem? Noise? Port selection?
Signal source is Rigol DS1064B Oscilloscope - port is connected to signal generator directly.

Thanks

2

Are you sure that G120 gave better results? They both use the same code. It is a simple software timer.

3

G120HDR result:

503;
497;
502;
501;
496;
502;
503;
497;
502;
497;
503;
495;
501;
503;
497;
503;
497;
502;
498;
501;

A few days ago I measured even better times on G120HDR. I can’t say what caused worsening. It seems that interrupts are triggered differently, on different levels. (?)

4

Interesting results. We will investigate.

5

would ambient temperature and/or crystal accuracy have anything to do with this?

6

Thank you. Another strenge behavior. SignalCapture do not respect parameter Port.InterruptMode.InterruptEdgeHigh. If “InterruptEdgeHigh” means every rising edge I should get time of one period. But with constant frequency I get:

2094;
7813;
2062;
7813;
2093;
7813;
2094;
7812;
2094;
7812;
2063;
7812;
2094;
7813;
2093;
7813;
2094;
7781;
2094;
7812;
2094;
7812;
2094;

Duty cycle of measured signal is approx. 21%.

7

@ Adam -

Nothing wrong in the firmware, just we use 32768 slow clock for time counter, so it can be different about 30us.
We improved it for next release.

8

OK. When the new release comes out? I am in trouble now… Could you send me prerelease version of assembly please?

9

@ Adam - It is a change in the firmware that still needs some testing. It will be in the next pre-release. We do not have a specific date yet, but it won’t be too long.