Re: [PATCH v2] iio: imu: inv_icm42600: avoid frequent timestamp jitter

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Hello Jonathan,

kernel test robot reported an issue with the patch v2. A direct 64 bits division was done without using div_* operators.

I just sent a patch v3 that is fixing the issue (tested on my side by compiling on PARISC architecture as done by kernel test robot).

Thanks and sorry for the error,
JB


From: Jonathan Cameron <jic23@xxxxxxxxxx>
Sent: Saturday, May 20, 2023 18:26
To: INV Git Commit <INV.git-commit@xxxxxxx>
Cc: linux-iio@xxxxxxxxxxxxxxx <linux-iio@xxxxxxxxxxxxxxx>; lars@xxxxxxxxxx <lars@xxxxxxxxxx>; Jean-Baptiste Maneyrol <Jean-Baptiste.Maneyrol@xxxxxxx>
Subject: Re: [PATCH v2] iio: imu: inv_icm42600: avoid frequent timestamp jitter 
 
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======================================================================
On Mon, 15 May 2023 10:06:45 +0000
inv.git-commit@xxxxxxx wrote:

> From: Jean-Baptiste Maneyrol <jean-baptiste.maneyrol@xxxxxxx>
> 
> We are currently synchronizing every time the data timestamp with
> the IT timestamp, leading to system jitter jamming timestamps.
> To fix that and keep it simple, let's just synchronize when the
> delta is bigger than the acceptable jitter, and keep
> synchronization at the jitter value.
> 
> The result is much stable timestamps reflecting better the real
> physical value. Example @50Hz delta timestamp,
> * before: 20.123ms, 19.721ms, 20.023ms, 20.353ms, 19.821ms, ...
> * after: 20.173ms, 20.173ms, 20.173ms, 20.40ms, 20.173ms, ...
> 
> Refactorize code and delete the unnecessary handling of multiple
> FIFO data.
> 
> Signed-off-by: Jean-Baptiste Maneyrol <jean-baptiste.maneyrol@xxxxxxx>

Applied to the togreg branch of iio.git and pushed out as testing for 0day
to poke at it.

Jonathan

> ---
>  .../imu/inv_icm42600/inv_icm42600_timestamp.c | 49 ++++++++++---------
>  1 file changed, 26 insertions(+), 23 deletions(-)
> 
> diff --git a/drivers/iio/imu/inv_icm42600/inv_icm42600_timestamp.c b/drivers/iio/imu/inv_icm42600/inv_icm42600_timestamp.c
> index 7f2dc41f807b..af2e59fb7258 100644
> --- a/drivers/iio/imu/inv_icm42600/inv_icm42600_timestamp.c
> +++ b/drivers/iio/imu/inv_icm42600/inv_icm42600_timestamp.c
> @@ -93,8 +93,8 @@ static bool inv_validate_period(uint32_t period, uint32_t mult)
>                return false;
>  }
>  
> -static bool inv_compute_chip_period(struct inv_icm42600_timestamp *ts,
> -                                 uint32_t mult, uint32_t period)
> +static bool inv_update_chip_period(struct inv_icm42600_timestamp *ts,
> +                                uint32_t mult, uint32_t period)
>  {
>        uint32_t new_chip_period;
>  
> @@ -104,10 +104,31 @@ static bool inv_compute_chip_period(struct inv_icm42600_timestamp *ts,
>        /* update chip internal period estimation */
>        new_chip_period = period / mult;
>        inv_update_acc(&ts->chip_period, new_chip_period);
> +     ts->period = ts->mult * ts->chip_period.val;
>  
>        return true;
>  }
>  
> +static void inv_align_timestamp_it(struct inv_icm42600_timestamp *ts)
> +{
> +     int64_t delta, jitter;
> +     int64_t adjust;
> +
> +     /* delta time between last sample and last interrupt */
> +     delta = ts->it.lo - ts->timestamp;
> +
> +     /* adjust timestamp while respecting jitter */
> +     jitter = ((int64_t)ts->period * INV_ICM42600_TIMESTAMP_JITTER) / 100;
> +     if (delta > jitter)
> +             adjust = jitter;
> +     else if (delta < -jitter)
> +             adjust = -jitter;
> +     else
> +             adjust = 0;
> +
> +     ts->timestamp += adjust;
> +}
> +
>  void inv_icm42600_timestamp_interrupt(struct inv_icm42600_timestamp *ts,
>                                      uint32_t fifo_period, size_t fifo_nb,
>                                      size_t sensor_nb, int64_t timestamp)
> @@ -116,7 +137,6 @@ void inv_icm42600_timestamp_interrupt(struct inv_icm42600_timestamp *ts,
>        int64_t delta, interval;
>        const uint32_t fifo_mult = fifo_period / INV_ICM42600_TIMESTAMP_PERIOD;
>        uint32_t period = ts->period;
> -     int32_t m;
>        bool valid = false;
>  
>        if (fifo_nb == 0)
> @@ -130,10 +150,7 @@ void inv_icm42600_timestamp_interrupt(struct inv_icm42600_timestamp *ts,
>        if (it->lo != 0) {
>                /* compute period: delta time divided by number of samples */
>                period = div_s64(delta, fifo_nb);
> -             valid = inv_compute_chip_period(ts, fifo_mult, period);
> -             /* update sensor period if chip internal period is updated */
> -             if (valid)
> -                     ts->period = ts->mult * ts->chip_period.val;
> +             valid = inv_update_chip_period(ts, fifo_mult, period);
>        }
>  
>        /* no previous data, compute theoritical value from interrupt */
> @@ -145,22 +162,8 @@ void inv_icm42600_timestamp_interrupt(struct inv_icm42600_timestamp *ts,
>        }
>  
>        /* if interrupt interval is valid, sync with interrupt timestamp */
> -     if (valid) {
> -             /* compute measured fifo_period */
> -             fifo_period = fifo_mult * ts->chip_period.val;
> -             /* delta time between last sample and last interrupt */
> -             delta = it->lo - ts->timestamp;
> -             /* if there are multiple samples, go back to first one */
> -             while (delta >= (fifo_period * 3 / 2))
> -                     delta -= fifo_period;
> -             /* compute maximal adjustment value */
> -             m = INV_ICM42600_TIMESTAMP_MAX_PERIOD(ts->period) - ts->period;
> -             if (delta > m)
> -                     delta = m;
> -             else if (delta < -m)
> -                     delta = -m;
> -             ts->timestamp += delta;
> -     }
> +     if (valid)
> +             inv_align_timestamp_it(ts);
>  }
>  
>  void inv_icm42600_timestamp_apply_odr(struct inv_icm42600_timestamp *ts,




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