CVS commit: src/sys/arch

["Jared D. McNeill" <jmcneill%netbsd.org@localhost>]

Module Name:    src
Committed By:   jmcneill
Date:           Sat Oct 19 12:34:10 UTC 2024

Modified Files:
        src/sys/arch/evbppc/wii: machdep.c
        src/sys/arch/powerpc/powerpc: clock.c

Log Message:
Improve delay() accuracy on Nintendo Wii.

The PowerPC delay() implementation converts the timebase frequency to
a number of nanoseconds per tick and uses that value to compute the
delay interval. On the Wii's Broadway processor with a timebase
frequency of 60.75 MHz, some precision is lost as each tick is
approximately 16.46 nanoseconds. The end result is that we sleep for
approximately 2.875% longer than necessary. This also has an impact
on CPU speed calculation on Broadway, which incorrectly reports itself
as 750MHz instead of 729MHz (2.875% faster).

Fix this by introducing an (optional) ticks_per_msec variable that can
be set by the platform and allows delay() to improve the accuracy of
longer delays.

Measured CPU frequency before this change:
[     1.000000] cpu0: 750.00 MHz, 256KB WB with ECC L2 cache

Measured CPU frequency after this change:
[     1.000000] cpu0: 729.00 MHz, 256KB WB with ECC L2 cache


To generate a diff of this commit:
cvs rdiff -u -r1.7 -r1.8 src/sys/arch/evbppc/wii/machdep.c
cvs rdiff -u -r1.18 -r1.19 src/sys/arch/powerpc/powerpc/clock.c

Please note that diffs are not public domain; they are subject to the
copyright notices on the relevant files.