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absindx / SNES-TestRoms

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[SA-1 RAM protection test] BW-RAM size detection is incorrect for boards without BW-RAM #2

Open absindx opened 3 months ago

absindx commented 3 months ago

image

When running on an SA-1 board where there is no BW-RAM present, the size of the BW-RAM is reported as 2 bytes.
It is speculated that some of the memory tests are passing due to the behavior of the BW-RAM open bus.

Test environment

Cartridge board image image

absindx commented 2 weeks ago

A simple fix has been implemented and it is included in the 20241020 release.
However, cartridges with only 1 byte of RAM will still be detected as having 0 bytes.

This is because the SA-1 openbus has a 1-byte latch, which makes it look like RAM.
For correct detection, the presence or absence of BW-RAM is determined from the SA-1 side.
The SNES side can only access the SA-1 openbus from the BW-RAM area, but the SA-1 side can access it from other areas.