Tuesday, September 20, 2016

Problem with driver board seems to be with RAM write and read

More woodwork today with Diablo tool work in the afternoon in between tasks. Once the last pieces are painted, I can nail them down and this facade is ready to be assembled on site this weekend.

Roof behind columns
Sign to install near roofline

I discovered that slide switch 6 is not working on the Digilent board I am using - just a random defect of some sort. Everything else appears to work, most likely this is a failure in the switch itself.

I am directly watching the pattern generator output and the bits being emitted don't match what should be delivered. I was not sure if the pattern itself is malfunctioning or that the problem is in the way the driver logic is recognizing sync words and other data.

I programmed the analyzer to give me symbolic names for the state machines I am tracking - much easier to interpret than the binary digits emitted from the board. It will help me see if the logic is going awry somewhere.

I am seeing the state machine correctly collect the words as it should see them based on the pattern generator, therefore I have to turn my attention to whether I am writing properly to the on board RAM. I looked over examples of how this is addressed by Digilent reference code and adjusted my logic accordingly.

Logic simulator results look correct, so time to run this transactionally from the PC. The advantage of the built in test pattern generator is that I can trigger a read sector, it should write the results to memory, and then I can read out the words using the Adept utility. I should quickly see whether I wrote the proper data or not

The results were disappointing. The logic analyzer showed me triggering the writes with the proper extracted word, but when I read the RAM back afterwards nothing had been written there. I ran out of time tonight, but the resolution to this will require me to significantly reinstrument the signals going out to the logic analyzer, so that I can watch the RAM signals myself.

The big open question is whether the signal quality from the real Diablo drive through my level shifters will give me a good clean read of the sector. I need to hook up to the drive at our next session on Friday.

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