WonderMCA

Where we were

Since the summer WonderMCA has worked on every PS/2 I own… as long as you did not look too closely at the 386DX machines. On the 286 and 386SX boxes (8550Z, 8555, 8556, 8557) the card was solid. On the Model 70 (8570), the same card, the same firmware and the same CPLD produced a slow drip of problems that never pointed at anything:

• at power-on the BIOS sometimes said “Memory change: Reset the RAM Config”, meaning the card’s configuration block had been changed behind its back;
• DIR C: could reboot the machine;
• loading a 67 KB .EXE from the emulated floppy rebooted the PC before the program even started.

This post is the story of the last few weeks. It covers five things that turned out to be linked more than I expected:

1. finding the real cause of the 8570 instability (spoiler: SmartDrive, and four