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drivers/periph_ptp: fix adjustment API

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The clock adjustment API only used a 16 bit integer for speed correction. This
is to course grained to allow compensating clock drifts at high accuracy.
Using a 32 bit integer instead would allow to fix for a drift of up to
about 1 nanosecond drift per each 5 seconds.

That ought to be enough for anyone! (*cough* *cough*)
This commit is contained in:
Marian Buschsieweke 2021-02-10 09:55:52 +01:00
parent 609c9ada34
commit acd9f4cc1a
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1 changed files with 4 additions and 4 deletions
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8
drivers/include/periph/ptp.h
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@ -216,18 +216,18 @@ void ptp_init(void);
*
* 1. A call with @p correction set to `0` restores the nominal clock speed.
* 2. A call with a positive value for @p correction speeds the clock up
* by `correction / (1 << 16)` (so up to ~50% for `INT16_MAX`).
* by `correction / (1 << 32)` (so up to ~50% for `INT32_MAX`).
* 3. A call with a negative value for @p correction slows the clock down by
* `-correction / (1 << 16)` (so up to 50% for `INT16_MIN`).
* `-correction / (1 << 32)` (so up to 50% for `INT32_MIN`).
*
* This allows the clock speed to be adjusted in steps ± 0.00153% in relation
* This allows the clock speed to be adjusted in steps ± 2.3284E-08 % in relation
* to its nominal clock speed, thus, allowing to counter systematic clock drift.
* In addition, this is intended to "smoothly" synchronize the clock over time
* to avoid jumps in the system time. (Especially calling @ref ptp_clock_adjust
* with negative values might be something to avoid, when applications are not
* prepared with clocks going backwards.)
*/
void ptp_clock_adjust_speed(int16_t correction);
void ptp_clock_adjust_speed(int32_t correction);
/**
* @brief Adjust the PTP clock as given