| Message ID | b91d1c8c-2467-44bc-b8bc-adc74dfb9bee@rwthex-w2-a.rwth-ad.de (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On Thu, 21 Dec 2017 19:31:36 +0100 Stefan Brüns <stefan.bruens@rwth-aachen.de> wrote: > The iio timestamp clock is user selectable and may be non-monotonic. Also, > only part of the acquisition time is measured, thus the delay was longer > than intended. > > Use a monotonic timestamp to track the time for the next poll iteration. > The timestamp is advanced by the sampling interval each iteration. In case > the conversion overrruns the register readout (i.e. fast sampling combined > with a slow bus), one or multiple samples will be dropped. > > Signed-off-by: Stefan Brüns <stefan.bruens@rwth-aachen.de> Applied to the togreg branch of iio.git and pushed out as testing for the autobuilders to play with it. Thanks, Jonathan > > --- > > Changes in v2: > - add a comment mentioning skipping samples on overrun > > drivers/iio/adc/ina2xx-adc.c | 41 +++++++++++++++++++++++++++-------------- > 1 file changed, 27 insertions(+), 14 deletions(-) > > diff --git a/drivers/iio/adc/ina2xx-adc.c b/drivers/iio/adc/ina2xx-adc.c > index 2621a34ee5c6..415e53b5c0a6 100644 > --- a/drivers/iio/adc/ina2xx-adc.c > +++ b/drivers/iio/adc/ina2xx-adc.c > @@ -703,10 +703,10 @@ static int ina2xx_work_buffer(struct iio_dev *indio_dev) > /* data buffer needs space for channel data and timestap */ > unsigned short data[4 + sizeof(s64)/sizeof(short)]; > int bit, ret, i = 0; > - s64 time_a, time_b; > + s64 time; > unsigned int alert; > > - time_a = iio_get_time_ns(indio_dev); > + time = iio_get_time_ns(indio_dev); > > /* > * Because the timer thread and the chip conversion clock > @@ -752,11 +752,9 @@ static int ina2xx_work_buffer(struct iio_dev *indio_dev) > data[i++] = val; > } > > - time_b = iio_get_time_ns(indio_dev); > + iio_push_to_buffers_with_timestamp(indio_dev, data, time); > > - iio_push_to_buffers_with_timestamp(indio_dev, data, time_a); > - > - return (unsigned long)(time_b - time_a) / 1000; > + return 0; > }; > > static int ina2xx_capture_thread(void *data) > @@ -764,7 +762,9 @@ static int ina2xx_capture_thread(void *data) > struct iio_dev *indio_dev = data; > struct ina2xx_chip_info *chip = iio_priv(indio_dev); > int sampling_us = SAMPLING_PERIOD(chip); > - int buffer_us, delay_us; > + int ret; > + struct timespec64 next, now, delta; > + s64 delay_us; > > /* > * Poll a bit faster than the chip internal Fs, in case > @@ -773,15 +773,28 @@ static int ina2xx_capture_thread(void *data) > if (!chip->allow_async_readout) > sampling_us -= 200; > > + ktime_get_ts64(&next); > + > do { > - buffer_us = ina2xx_work_buffer(indio_dev); > - if (buffer_us < 0) > - return buffer_us; > + ret = ina2xx_work_buffer(indio_dev); > + if (ret < 0) > + return ret; > > - if (sampling_us > buffer_us) { > - delay_us = sampling_us - buffer_us; > - usleep_range(delay_us, (delay_us * 3) >> 1); > - } > + ktime_get_ts64(&now); > + > + /* > + * Advance the timestamp for the next poll by one sampling > + * interval, and sleep for the remainder (next - now). > + * In case "next" has already passed, the interval is added > + * multiple times, i.e. samples are dropped. > + */ > + do { > + timespec64_add_ns(&next, 1000 * sampling_us); > + delta = timespec64_sub(next, now); > + delay_us = timespec64_to_ns(&delta) / 1000; > + } while (delay_us <= 0); > + > + usleep_range(delay_us, (delay_us * 3) >> 1); > > } while (!kthread_should_stop()); > -- To unsubscribe from this list: send the line "unsubscribe linux-iio" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
diff --git a/drivers/iio/adc/ina2xx-adc.c b/drivers/iio/adc/ina2xx-adc.c index 2621a34ee5c6..415e53b5c0a6 100644 --- a/drivers/iio/adc/ina2xx-adc.c +++ b/drivers/iio/adc/ina2xx-adc.c @@ -703,10 +703,10 @@ static int ina2xx_work_buffer(struct iio_dev *indio_dev) /* data buffer needs space for channel data and timestap */ unsigned short data[4 + sizeof(s64)/sizeof(short)]; int bit, ret, i = 0; - s64 time_a, time_b; + s64 time; unsigned int alert; - time_a = iio_get_time_ns(indio_dev); + time = iio_get_time_ns(indio_dev); /* * Because the timer thread and the chip conversion clock @@ -752,11 +752,9 @@ static int ina2xx_work_buffer(struct iio_dev *indio_dev) data[i++] = val; } - time_b = iio_get_time_ns(indio_dev); + iio_push_to_buffers_with_timestamp(indio_dev, data, time); - iio_push_to_buffers_with_timestamp(indio_dev, data, time_a); - - return (unsigned long)(time_b - time_a) / 1000; + return 0; }; static int ina2xx_capture_thread(void *data) @@ -764,7 +762,9 @@ static int ina2xx_capture_thread(void *data) struct iio_dev *indio_dev = data; struct ina2xx_chip_info *chip = iio_priv(indio_dev); int sampling_us = SAMPLING_PERIOD(chip); - int buffer_us, delay_us; + int ret; + struct timespec64 next, now, delta; + s64 delay_us; /* * Poll a bit faster than the chip internal Fs, in case @@ -773,15 +773,28 @@ static int ina2xx_capture_thread(void *data) if (!chip->allow_async_readout) sampling_us -= 200; + ktime_get_ts64(&next); + do { - buffer_us = ina2xx_work_buffer(indio_dev); - if (buffer_us < 0) - return buffer_us; + ret = ina2xx_work_buffer(indio_dev); + if (ret < 0) + return ret; - if (sampling_us > buffer_us) { - delay_us = sampling_us - buffer_us; - usleep_range(delay_us, (delay_us * 3) >> 1); - } + ktime_get_ts64(&now); + + /* + * Advance the timestamp for the next poll by one sampling + * interval, and sleep for the remainder (next - now). + * In case "next" has already passed, the interval is added + * multiple times, i.e. samples are dropped. + */ + do { + timespec64_add_ns(&next, 1000 * sampling_us); + delta = timespec64_sub(next, now); + delay_us = timespec64_to_ns(&delta) / 1000; + } while (delay_us <= 0); + + usleep_range(delay_us, (delay_us * 3) >> 1); } while (!kthread_should_stop());
The iio timestamp clock is user selectable and may be non-monotonic. Also, only part of the acquisition time is measured, thus the delay was longer than intended. Use a monotonic timestamp to track the time for the next poll iteration. The timestamp is advanced by the sampling interval each iteration. In case the conversion overrruns the register readout (i.e. fast sampling combined with a slow bus), one or multiple samples will be dropped. Signed-off-by: Stefan Brüns <stefan.bruens@rwth-aachen.de> --- Changes in v2: - add a comment mentioning skipping samples on overrun drivers/iio/adc/ina2xx-adc.c | 41 +++++++++++++++++++++++++++-------------- 1 file changed, 27 insertions(+), 14 deletions(-)