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Use same USB_PLL default setting as the C SDK #688

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merged 2 commits into from
Nov 10, 2023

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@jannic jannic commented Sep 14, 2023

The previously used settings used a VCO clock of 480MHz, which is outside the valid range (750MHz - 1600MHz) given by the datasheet since revision 1.8.

There are several valid VCO values, and there is a tradeoff between lower jitter and lower power consumption. So it's not obvious which value would be the best default.

Instead of doing our own guesswork, use the same value as the C SDK: https://github.com/raspberrypi/pico-sdk/pull/869/files

This patch only changes the default value, but doesn't update the input validation. So it's still possible to manually specify a VCO frequency outside the updated range, as long as it's in the more lenient range specified by older datasheet revisions, 400MHz - 1600MHz.

The previously used settings used a VCO clock of 480MHz, which is
outside the valid range (750MHz - 1600MHz) given by the datasheet since
revision 1.8.

There are several valid VCO values, and there is a tradeoff between
lower jitter and lower power consumption. So it's not obvious which
value would be the best default.

Instead of doing our own guesswork, use the same value as the C SDK:
https://github.com/raspberrypi/pico-sdk/pull/869/files

This patch only changes the default value, but doesn't update the
input validation. So it's still possible to manually specify a VCO
frequency outside the updated range, as long as it's in the more lenient
range specified by older datasheet revisions, 400MHz - 1600MHz.
@jannic jannic added this to the 0.9.1 milestone Oct 22, 2023
@jannic jannic added the non-breaking change This pull requests contains a minor, not SemVer breaking, change label Oct 22, 2023
@jannic jannic merged commit 8a68410 into rp-rs:main Nov 10, 2023
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@jannic jannic deleted the change-pll-settings branch November 10, 2023 08:27
ithinuel added a commit that referenced this pull request Feb 22, 2024
This completes the change introduced in #688 to update the valid range for VCO’s frequency.

Note: this change was left off until now because it was a breaking change.
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