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SimoneN64 / Kaizen

Experimental Nintendo 64 emulator
https://gadolinium.dev
BSD 3-Clause "New" or "Revised" License
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Wrong TLB index mask? #105

Closed tamaroning closed 1 year ago

tamaroning commented 1 year ago

Very small nit, but should this mask be 0b11111? It is also true for elsewhere index is used. https://github.com/SimoneN64/Kaizen/blob/74dccb6ac6a679acbf41b497151e08af6302b0e9/src/backend/core/interpreter/cop/cop0instructions.cpp#L35

SimoneN64 commented 1 year ago

It's not 5 bits no, it is 6, like my mask, at least to my knowledge. Will research further to investigate if my understanding is correct. Will leave the issue opened

bigbass1997 commented 1 year ago

If the function is only interested in the index field of the register, then masking a 6 bit wide value is accurate. bit-31 is also readable/writable.

The VR4300 manual does note that while the index field is 6 bits wide, only the least-significant 5 bits are actually used in TLB operations (page 146). Perhaps this is where the confusion is from?

The bit mask has be confirmed via an addition to the n64-systemtest suite: https://github.com/lemmy-64/n64-systemtest/pull/57

SimoneN64 commented 1 year ago

Alright, can close this issue as its been tested as right.