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| author | Nicolas Boichat <drinkcat@chromium.org> | 2019-06-23 20:47:22 +0800 |
|---|---|---|
| committer | Commit Bot <commit-bot@chromium.org> | 2019-06-24 06:45:17 +0000 |
| commit | 81d5f99910334d09768593519767f571392c5238 (patch) | |
| tree | d8da9a36959e5b8ac20fb791f15e890e946a8485 | |
| parent | 5d4f631acf5ef95a8893d3f91512ed549f105ec0 (diff) | |
| download | chrome-ec-81d5f99910334d09768593519767f571392c5238.tar.gz | |
chip/mt_scp/clock: Prefer closest frequency when calibrating
It's better to chose the closest possible frequency, rather than
the one above the target, as the system clock is now sourced from
ULPOSC1 and we want to minimize errors.
BRANCH=none
BUG=b:120176040
TEST=Load kukui_scp, see that ULPOSC is calibrated to 247558 kHz,
instead of 250148 kHz (0.18% error, instead of 0.87%)
Change-Id: I068fa09b5fedaf795ee6171f0b88ab658d5792a9
Signed-off-by: Nicolas Boichat <drinkcat@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/ec/+/1672655
Reviewed-by: Yilun Lin <yllin@chromium.org>
| -rw-r--r-- | chip/mt_scp/clock.c | 11 |
1 files changed, 7 insertions, 4 deletions
diff --git a/chip/mt_scp/clock.c b/chip/mt_scp/clock.c index 8214f5ae15..edc50d5939 100644 --- a/chip/mt_scp/clock.c +++ b/chip/mt_scp/clock.c @@ -198,8 +198,10 @@ static int scp_calibrate_ulposc(int osc, int target_mhz) /* * In the loop below, linear search closest div value to get desired * frequency counter value. Then adjust cali to get a better result. - * Note that this doesn't give optimal output frequency, and we prefer - * a frequency slightly above our target. + * Note that this doesn't give optimal output frequency, but it's + * usually close enough. + * TODO(b:120176040): See if we can efficiently calibrate the clock with + * more precision by exploring more of the cali/div space. * * The frequency function follows. Note that f is positively correlated * with both div and cali: @@ -215,11 +217,12 @@ static int scp_calibrate_ulposc(int osc, int target_mhz) /* * If previous and current are on either side of the desired - * frequency, pick the one above the desired frequency. + * frequency, pick the closest one. */ if (prev.freq && signum(target_freq - curr.freq) != signum(target_freq - prev.freq)) { - if (prev.freq > curr.freq) + if (abs(target_freq - prev.freq) < + abs(target_freq - curr.freq)) curr = prev; if (stage == STAGE_CALI) |