hoglet wrote:
Dr Jefyll wrote:
Yes, why would avoiding the additional transitions make a difference? Maybe I missed something, but I thought that, even with the extra transitions, the data still settled soon enough.
I agree, there should be plenty of time for the signals to settle. So something else has to be going on here.
Indeed, that was my assumption as well, there should have been enough time to settle
Quote:
Those extra transitions are probably happening on all the RAM outputs simultaneously. So I was wondering if the actual issue is ground bounce bad enough to cause corruption of the RAM contents.
I had one question for fachat: does your RAM test indicate whether it was a read or a write that failed? It would be very useful to know whether re-reading the failed address produces consistently wrong data.
Dave
The RAM test actually indicates that. However, I have just looked through my pictures I took from the test, and found I only had what I call "secondary" errors - problems that appear in the dRAM test. Those were definitely of read and of write type (where the test just re-checks the memory content if it did not match. If the second read matches the should-be value, I classify as read error, if not, independent of value, I classify as write). These completely go away as well now.
My assumption is that they were caused by wrong memory accesses during the test, that actually runs in the SRAM that has the problem. It might be something else though, as I am actually wondering why actual crashes appear so seldomly (if at all)
One picture above actually shows quite some signal bouncing on the /CS line shortly after Phi2 goes high - maybe that is caused by ground bounce, that may cause other havoc.
Edit: it's actually the picture in the post on the top of this page, and it actually does show SRAM ground bouncing, but my problem is what is the reference?
I don't really have experience measuring the ground bounce though - what is the best way to measure that? Use two probes between the different (which) ground points, or between ground and VCC, and let the scope do a diff?
André
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