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Aarch32: CLK_MAGIC, CLK_SHIFT inconsistencies #1352

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Indanz opened this issue Nov 19, 2024 · 1 comment

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Indanz commented Nov 19, 2024 •

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What is the correct value as input to the kernel/tools/reciprocal.py script? The value in HZ or the value in MHz?

For example, for TIMER_FREQUENCY 24000000:

am335x, exynos4/5 have CLK_MAGIC 2863311531llu and CLK_SHIFT 36u as they used 24 MHz as input.
odroidc2/4 have CLK_MAGIC 375299969llu and CLK_SHIFT 53u as they used the HZ value as input.

I haven't checked all other boards, but surely using the wrong values would mess up timing?

The text was updated successfully, but these errors were encountered:

Contributor Author

Indanz commented Nov 19, 2024

Looking at the code (assuming USE_KHZ is false) it does:

static inline CONST time_t ticksToUs(ticks_t ticks)
{
    /* simulate 64bit division using multiplication by reciprocal */
    return (ticks * CLK_MAGIC) >> CLK_SHIFT;
}

So it seems that using 24 as input is the correct thing to do and that the odroid defines are wrong.

Not sure what you're supposed to do when you don't have a round MHz value and USE_KHZ is true though.

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