I’m beginning to suspect there’s something subtly wrong with my Apple IIe, which might explain a lot of strange intermittent errors I’ve recently observed with Yellowstone and Floppy Emu development. It’s hard to know what to conclude, but when you can’t trust your test equipment, it’s impossible to trust the validity of your test results.
Recently I used this Apple IIe to test my new Floppy Emu OLED prototype board. When connected to a standard Apple Disk 5.25 controller card, everything worked fine initially. But when I tried doing some ProDOS file copy operations, the Floppy Emu spontaneously reset to the happy face / self-test screen. DOH! I tried it twice, and the Emu reset itself during the copy operation both times. I concluded there must be something wrong with the prototype board.
Then I tried the copy test two more times, and got different results. The Emu prototype didn’t reset itself, but the OLED display went blank several times during the copy operations. Hmmm.
So then I tried a plain vanilla Floppy Emu Model B, the same hardware and firmware that I’ve been using successfully for more than a year. I found that when trying to boot the Apple IIe from a ProDOS v1.9 disk image, the Model B’s LCD went blank several times during booting. Huh? This happened in two consecutive test runs, but then mysteriously stopped happening. I also tried the same file copy operations I’d done with the OLED prototype board, and saw a similar behavior where the LCD went blank a few times during the copy. But as before, after reproducing the bug twice in a row, it stopped happening.
Finally I went back to the OLED prototype board, and this time everything worked fine. No more unexplained resets or display blank-outs.
Maybe there’s something wrong with the Apple IIe’s power supply, or some problem where it needs to warm-up for a while before it works reliably? My first OLED prototype board tests were the first time I’d powered on the Apple IIe in several days, so it was cold. During an hour of testing, the strange Floppy Emu problems I’d observed gradually disappeared. It doesn’t really make sense to me, but it’s the best explanation I can think of. This might also explain some strange unexpected resets of the Floppy Emu last month, when I tested it with the Yellowstone card. In fact, it casts doubt on all of my Yellowstone testing.