Brad Robinson

Issues reading SD Card on Classic Computing Shield

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Hi All,

First post here...

I'm in the process of porting my FPGA 80's home computer to Papilio Duo but currently stumped by the SD card.  I'm using a Papilio Duo and a Classic Computing Shield.

What I'm seeing is exactly like what's described in this post -  Basically the card initializes correctly as SDHC, a read command is issued, the read response returns success, the lead token on the data packet comes back as expected, but the data is all zeros.  I've double checked the data on the card multiple times and it definitely contains data.

The cause of the problem in the above post was related to voltage drops once the read starts.  ie: the card initialization and most register related commands worked but any access to the actual memory resulted in zero data due to a 2v drop.

So... I'm wondering if this might be a problem with the way I'm powering the board or with the shield itself.  I'm powering it via USB port from my Macbook but have also tried USB plugged straight into a iPhone charger.

Anyone else seen issues like this?  Any help resolving this would be much appreciated including suggestions of other projects/designs that are known to work that I could use for testing the hardware side of things.


btw: here's the details on my project - - it's an FPGA emulation of a Microbee which was an 80's home computer designed and built here in Australia.

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Thanks!  I'll look into some of these options.  In the meantime I haven't had much time to play with it, but I've tried 3 or 4 other cards now and still no luck.

I'll post back when I figure it out.

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Follow up... I finally figured it out.  It was a combination of block number miscalculations and some timing errors in my design.  The SD slot on classic computing shield works fine with both SD and SDHC cards (at least the ones I have).

Thanks for the help.

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