On Sun, 23 Jun 2019 14:29:10 +0200
Andreas Klinger <ak@xxxxxxxxxxxxx> wrote:
> The measured time value in the driver is limited to the maximum distance
> which can be read by the sensor. This limitation was wrong and is fixed
> by this patch.
>
> It also takes into account that we are supporting a variety of sensors
> today and that the recently added sensors have a higher maximum
> distance range.
>
> Suggested-by: Zbyněk Kocur <zbynek.kocur@xxxxxxxxxxx>
> Signed-off-by: Andreas Klinger <ak@xxxxxxxxxxxxx>
Ideally I'm looking for Zbyněk to confirm that this addresses the
original question.
Thanks,
Jonathan
> ---
> drivers/iio/proximity/srf04.c | 29 +++++++++++++++--------------
> 1 file changed, 15 insertions(+), 14 deletions(-)
>
> diff --git a/drivers/iio/proximity/srf04.c b/drivers/iio/proximity/srf04.c
> index 8b50d56b0a03..01eb8cc63076 100644
> --- a/drivers/iio/proximity/srf04.c
> +++ b/drivers/iio/proximity/srf04.c
> @@ -110,7 +110,7 @@ static int srf04_read(struct srf04_data *data)
> udelay(data->cfg->trigger_pulse_us);
> gpiod_set_value(data->gpiod_trig, 0);
>
> - /* it cannot take more than 20 ms */
> + /* it should not take more than 20 ms until echo is rising */
> ret = wait_for_completion_killable_timeout(&data->rising, HZ/50);
> if (ret < 0) {
> mutex_unlock(&data->lock);
> @@ -120,7 +120,8 @@ static int srf04_read(struct srf04_data *data)
> return -ETIMEDOUT;
> }
>
> - ret = wait_for_completion_killable_timeout(&data->falling, HZ/50);
> + /* it cannot take more than 50 ms until echo is falling */
> + ret = wait_for_completion_killable_timeout(&data->falling, HZ/20);
> if (ret < 0) {
> mutex_unlock(&data->lock);
> return ret;
> @@ -135,19 +136,19 @@ static int srf04_read(struct srf04_data *data)
>
> dt_ns = ktime_to_ns(ktime_dt);
> /*
> - * measuring more than 3 meters is beyond the capabilities of
> - * the sensor
> + * measuring more than 6,45 meters is beyond the capabilities of
> + * the supported sensors
> * ==> filter out invalid results for not measuring echos of
> * another us sensor
> *
> * formula:
> - * distance 3 m
> - * time = ---------- = --------- = 9404389 ns
> - * speed 319 m/s
> + * distance 6,45 * 2 m
> + * time = ---------- = ------------ = 40438871 ns
> + * speed 319 m/s
> *
> * using a minimum speed at -20 °C of 319 m/s
> */
> - if (dt_ns > 9404389)
> + if (dt_ns > 40438871)
> return -EIO;
>
> time_ns = dt_ns;
> @@ -159,20 +160,20 @@ static int srf04_read(struct srf04_data *data)
> * with Temp in °C
> * and speed in m/s
> *
> - * use 343 m/s as ultrasonic speed at 20 °C here in absence of the
> + * use 343,5 m/s as ultrasonic speed at 20 °C here in absence of the
> * temperature
> *
> * therefore:
> - * time 343
> - * distance = ------ * -----
> - * 10^6 2
> + * time 343,5 time * 106
> + * distance = ------ * ------- = ------------
> + * 10^6 2 617176
> * with time in ns
> * and distance in mm (one way)
> *
> - * because we limit to 3 meters the multiplication with 343 just
> + * because we limit to 6,45 meters the multiplication with 106 just
> * fits into 32 bit
> */
> - distance_mm = time_ns * 343 / 2000000;
> + distance_mm = time_ns * 106 / 617176;
>
> return distance_mm;
> }
