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READ!

A project log for sdramThing4.5 "Logic Analyzer"

An AVR, 128MB SDRAM DIMM, old laptop LCD, and a handful of TTL chips -- 30+MS/s 32-channel logic-analyzer interface for an analog 'scope

eric-hertzEric Hertz 03/01/2015 at 10:480 Comments

I've finally reimplemented Read!

Yep... I've been working with this thing without the ability for the uC to *read* data written by the uC to the SDRAM...

Way back in the day, I had READ... I needed it to verify that the data was being written correctly. Turned out, way back then, that the problem was noise on my SDRAM's Clock line... I shielded that cable and found that the reliability was impeccable (zero errors in dozens of tests of 128MB)... So, It's not exactly that I *got rid* of READ, but that the software kept getting improved, and the hardware, as well, and at some point the old code for readback was no longer compatible with the new hardware... and, well, it was working so well for so long and continued to do-so for so long that I didn't bother to update the readback code to make it functional with the new designs.

So, now, it's reimplemented.

(As another beneficial aside, I've finally put the free-running sdram interface in my commonCode. It's designed, specifically, for Free-Running. But, now that READ's been reimplemented, there's no reason it couldn't be used as a *huge* (and plausibly somewhat slow) RAM for any project, free-running or not, only requiring a single 7451.)

The results?

It seems to work perfectly in the old configuration (with the one-shot circuitry removed from the system).

With the one-shot circuitry in logical-bypass mode (the old-configuration's signals going through an AND gate whose other pin is always active)... not so much.

I haven't analyzed it much, yet... it's late. But, of course, this would be the one tool that's probably the most important in debugging this thing... and I put it off for quite some time, doing all sorts of seemingly unrelated things (like commonCoding it, improving the comments, cleaning it up *substantially*, etc.)

Onward!

(Wait, wasn't this project supposed to get me working with a stepper-motor-driver? Man, I almost completely forgot about that).

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