Use TSC for QueryPerformance* API #695
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GXTX
reviewed
Jan 18, 2025
| // Chapter 2.22 of https://www.intel.com/content/dam/develop/external/us/en/documents/335592-sdm-vol-4.pdf | ||
| const uint64_t multiplier_pattern = (poweron_reg >> 22) & 0b101111; | ||
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| // https://web.archive.org/web/20040407043044/http://www.intel.com:80/design/mobile/datashts/29834006.pdf |
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Neither document mentioned in this PR has information on >10X multipliers, this is something I brought up (and wasn't answered) in xemu-project/xemu/pull/1551, I also attempted to search Linux and they too seem not to mention support for >10X. Where are you getting these numbers?
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From the CPUs, specifically SL6BY, SL6C6 and SL6C7.
Ryzee119
reviewed
Jan 19, 2025
Ryzee119
reviewed
Jan 19, 2025
We can measure the tsc freq with a reference clock |
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The first of these two commits changes our implementation of
QueryPerformanceCounterandQueryPerformanceFrequencyto use the TSC (like later XDKs did) instead of the kernel's less accurate internal counter.The second commit improves compatibility with non-stock Xbox systems by using a constructor to compute the TSC frequency on startup instead of using a hard-coded value.
It uses a lookup-table of known CPU clock multipliers and FSB divider and multiplier values from the northbridge to derive this frequency from the crystal frequency. This is done with 64 bit integer math and fractions of a Hz to not introduce any errors during the calculations.
The only way this could be wrong should be using a non-stock crystal frequency.
Using this code in xemu requires xemu-project/xemu#1551 so any reasonably recent version should do.
The code is almost unchanged from my old branch that wasn't upstreamed yet (https://github.com/thrimbor/nxdk/tree/tsc).
Supersedes #663