Fixing odd memory errors.

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I was having all sorts of random bad pixels in my frame buffer. Some build would be fine, others would have a lot of bad pixels.

Turns out that some of my signals weren't being packed into the I/O buffers, and were being fed from  FPGA fabric. Turning on "Pack I/O Registers/Latches into IOBs" in the mapping properties fixed this.

Hope it helps somebody!


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Two comments:

Comment One:

Yes, always pack outputs on IOB. But make sure all outputs are synchronous.

Comment Two:

I don't, cause I can't :) That kills my timing for the PPS stuff [every output is a huge muxer], so only core things [like VGA, SPI flash] are packed. Also, if you are reading from IOB make sure you properly sample your stuff and avoid metastability (add a latch+FF or two FF). Will delay signal, but signal will come out clean.

And Comment Three:

You made it again to Hack-a-Day, congratulations :)


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Guest monkeydoo

I'm going to try for another...

I got my FPGA board transmitting morse code 'SOS' on 25MHz with no added hardware, just a few lengths of wire.

Cool.  Now the killjoy part.  In realitity the output will be spectrally horrible.  Consider at the very least a low pass to attenuate all those nasty harmonics.  You will be " spewing "  garbage all over the spectrum :)

I know people who communicate all over the world with little more than a crystal oscillator and a length of wire !

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