Turns out I can get the SNASM2 card behaving on this Pentium-class motherboard by disabling the CPU’s internal cache through the BIOS. Why? I have no idea!

This was a workaround for this particular PC and development-card combination. I never established the underlying reason, so I would not treat “disable the CPU cache” as a general SNASM2 requirement. The 486DX4-100 system worked much more happily without this particular piece of nonsense.

Any and all speculation is welcome.