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RetroChallenge Log Entry #3: The Glitches are fixed!

A project log for 3D Graphics on the Microprofessor MPF-1B

RetroChallenge 2025/10 Blog

michael-wesselMichael Wessel 10/18/2025 at 13:560 Comments

The glitches seen in the previous video (Update #2) are fixed - this turned out to be completely unrelated to the MPF-GRAFX card, but was caused by PicoRAM Ultimate. An uncaught "glitch" in the SRAM emulation due to noisy ADC button decoding. I have pushed a firmware update to PicoRAM Ultimate and PicoRAM 6116. The problem was that due to bad and noisy ADC thresholds button presses were detected that weren't real. Now, each time a button press is registered, the SRAM emulation is temporarily halted... but it requires the Z80 WAIT line to be connected, which I had not. This caused the issues. Obviously, you can't just halt SRAM emulation and not halt the CPU and expect it to run properly. The problem was fixed by adjusting the ADC threshold levels in the UTLIMATE.INI (or, 6116.INI). But I added some UI Error Message now if such a "spurious" button press is detected caused by noisy ADC and inappropriate analog threshold levels in the init files. Hopefully, this will make the effect at least visible if it should happen again to someone. Because it really was a head scratcher, given that there was no visible indication for this error other than the CPU crashing or glitching. Now we at least see what's going on, and can the manually adjust the thresholds in the init files. Phew!

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