Added some new photos for A501 replacement
Added some new photos of the populated PCB for the Commodore Amiga A501 memory replacement card.
Find them on the main project page here.
Articles from Techtravels Amiga Blog
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Main project page updated with PCB timing diagram
Below is a label diagram of how the PCB is handling a read from the Amiga. (and partial theory of operation here too). As of 1/18/14, Schematics are coming.
Cause of original instability and boot problems on the original A500 identified
So the very first A500 I had been testing on since the beginning of the project had a Bug Katcher installed. It turns out that I wasn’t really using it, but I left it plugged in anyways.
I’m not sure electrically what the exact effects of having that installed are, but removing it caused all of my instability and boot issues to disappear.
I was able to boot the amiga (10) times in a row from a cold start without an associated hang.
Cause of original instability and boot problems on the original A500 identified
So the very first A500 I had been testing on since the beginning of the project had a Bug Katcher installed. It turns out that I wasn’t really using it, but I left it plugged in anyways.
I’m not sure electrically what the exact effects of having that installed are, but removing it caused all of my instability and boot issues to disappear.
I was able to boot the amiga (10) times in a row from a cold start without an associated hang.
Sweet success, card works 100% in different DUT(Amiga)
So I think the Amiga 500 I was testing with has problems. I’m not sure precisely what or why but
Today, I dropped my new A501 replacement card into a known-working Commodore Amiga 500. It fired up immediately no issues with booting, everything worked, no wonkiness, memory tests passed 100%. This amiga has an accelerator card, and I was able to run 300 tests of pretty much the entire memory space on the card in about 5 minutes. Everything worked without error.
I’d like to get more data points here before I call it DONE, but it looks GREAT to me!
Logic Analyzer probe loading seems to fix boot issue
While I had my logic analyzer connected to my memory card tonight, I noticed that I no longer had the white screen hang on bootup problem that I’ve been plagued with since this card came in.
As a matter of fact, it was booting up about 100% of the time.
I disconnected my HP logic analyzer probes, and all of a sudden, the Amiga won’t boot any longer.
It seems as if the impedance loading of the probes have been POSITIVELY affecting my circuit….slowing down the rise times and fixing whatever issue was in place.
Stress testing the memory board
So I’ve written some assembly in the monitor software I’ve been using, and I’ve just created a large loop to see if I can get the card to fail.
I’m still having plenty of problems on bootup, but everything else is checking on. So I’m not sure what the cause is, but I’m double checking that the memory system is reliable over a large number of reads/writes.
Workbench booted up with the new card installed!
For those of you who might not get the significance, workbench loads a number of libraries into the extended fast memory on bootup. As you can see in this image below, more fast memory is actually being used than the chip, onboard memory immediately after bootup.
RTC Progress
RTC appears to be working and keeping the date and time across cold-starts.
I picked the Epson RTC-72423 which is about a $6 chip, but is obviously directly compatible with the OKI Semiconductor MSM6242B. The design, including the battery supervisor, had never been tested — not even as a prototype… and appears to have worked the first time!
I needed to do a “setclock reset”, set the date via “Date 28-Dec-13 02:26:00″ command, and then did a “setclock save” Subsequent setclock loads brings it back!