Using Trackuino shield with FEZ Domino

NETMF & Gadgeteer
1

I would like to use the Trackuino with the FEZ Domino board. h/w-wise it’s a fit, it’s the s/w that’s an issue.

Handling the GPS is simple enough, it’s the 1200 baud AFSK modulation that is tricky. The Trackuino doesn’t use PWM, rather it drives a DAC from a table of sampled sine wave values. This produces a very clean sine wave for the 1200 and 2200 hz tones, but it requires cpu-intensive operations to feed the DAC (like 62,500 samples per second!).

I tried a similar approach on the Domino. The Domino supports an AnalogOut class that will take a buffer and feed it to the DAC. This doesn’t appear to be as efficient as the Trackuino, even with a 72Mhz clock, and can’t drive the DAC anywhere need the needed sampling interval. In addition there is significant overhead in setting up the tone, on the order of 150us, which is too much as a 1200hz tone is only 833us long.

Any suggestions? Why is a 72Mhz platform so much slower than a 16Mhz one? Is the .NET framework that much of an overhead?

2

Well, this kind of question has been posed multiple times. Simply put, the way the netmf works is much different to the way a traditional compiled app onto an embedded hardware works - really, the framework is an OS that sits on the hardware, that has its own needs. So that might just mean your specific task may not be suitable to use netmf on.

3

Also, if you need specific tight timing constructs, then RLP is the accepted way to deal with that.