| Message ID | 20180710181903.GA5386@arbeit (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On Tue, 10 Jul 2018 20:19:03 +0200 Andreas Klinger <ak@it-klinger.de> wrote: > On a system with parasitic capacitance it turned out that DOUT is not ready > after 100 ns after PD_SCK has raised. A measurement showed almost 1000 ns > until DOUT has reached its correct value. > > With this patch its now possible to wait until data is ready. > > The wait time should not be higher than the maximum PD_SCK high time which > is corresponding to the datasheet 50000 ns. > > Signed-off-by: Andreas Klinger <ak@it-klinger.de> Applied, thanks. Jonathan > --- > drivers/iio/adc/hx711.c | 39 +++++++++++++++++++++++++++++++++++++++ > 1 file changed, 39 insertions(+) > > diff --git a/drivers/iio/adc/hx711.c b/drivers/iio/adc/hx711.c > index 9430b54121e0..36b59d8957fb 100644 > --- a/drivers/iio/adc/hx711.c > +++ b/drivers/iio/adc/hx711.c > @@ -97,6 +97,14 @@ struct hx711_data { > * 2x32-bit channel + 64-bit timestamp > */ > u32 buffer[4]; > + /* > + * delay after a rising edge on SCK until the data is ready DOUT > + * this is dependent on the hx711 where the datasheet tells a > + * maximum value of 100 ns > + * but also on potential parasitic capacities on the wiring > + */ > + u32 data_ready_delay_ns; > + u32 clock_frequency; > }; > > static int hx711_cycle(struct hx711_data *hx711_data) > @@ -110,6 +118,14 @@ static int hx711_cycle(struct hx711_data *hx711_data) > */ > preempt_disable(); > gpiod_set_value(hx711_data->gpiod_pd_sck, 1); > + > + /* > + * wait until DOUT is ready > + * it turned out that parasitic capacities are extending the time > + * until DOUT has reached it's value > + */ > + ndelay(hx711_data->data_ready_delay_ns); > + > val = gpiod_get_value(hx711_data->gpiod_dout); > /* > * here we are not waiting for 0.2 us as suggested by the datasheet, > @@ -120,6 +136,12 @@ static int hx711_cycle(struct hx711_data *hx711_data) > gpiod_set_value(hx711_data->gpiod_pd_sck, 0); > preempt_enable(); > > + /* > + * make it a square wave for addressing cases with capacitance on > + * PC_SCK > + */ > + ndelay(hx711_data->data_ready_delay_ns); > + > return val; > } > > @@ -458,6 +480,7 @@ static const struct iio_chan_spec hx711_chan_spec[] = { > static int hx711_probe(struct platform_device *pdev) > { > struct device *dev = &pdev->dev; > + struct device_node *np = dev->of_node; > struct hx711_data *hx711_data; > struct iio_dev *indio_dev; > int ret; > @@ -530,6 +553,22 @@ static int hx711_probe(struct platform_device *pdev) > hx711_data->gain_set = 128; > hx711_data->gain_chan_a = 128; > > + hx711_data->clock_frequency = 400000; > + ret = of_property_read_u32(np, "clock-frequency", > + &hx711_data->clock_frequency); > + > + /* > + * datasheet says the high level of PD_SCK has a maximum duration > + * of 50 microseconds > + */ > + if (hx711_data->clock_frequency < 20000) { > + dev_warn(dev, "clock-frequency too low - assuming 400 kHz\n"); > + hx711_data->clock_frequency = 400000; > + } > + > + hx711_data->data_ready_delay_ns = > + 1000000000 / hx711_data->clock_frequency; > + > platform_set_drvdata(pdev, indio_dev); > > indio_dev->name = "hx711"; -- 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/hx711.c b/drivers/iio/adc/hx711.c index 9430b54121e0..36b59d8957fb 100644 --- a/drivers/iio/adc/hx711.c +++ b/drivers/iio/adc/hx711.c @@ -97,6 +97,14 @@ struct hx711_data { * 2x32-bit channel + 64-bit timestamp */ u32 buffer[4]; + /* + * delay after a rising edge on SCK until the data is ready DOUT + * this is dependent on the hx711 where the datasheet tells a + * maximum value of 100 ns + * but also on potential parasitic capacities on the wiring + */ + u32 data_ready_delay_ns; + u32 clock_frequency; }; static int hx711_cycle(struct hx711_data *hx711_data) @@ -110,6 +118,14 @@ static int hx711_cycle(struct hx711_data *hx711_data) */ preempt_disable(); gpiod_set_value(hx711_data->gpiod_pd_sck, 1); + + /* + * wait until DOUT is ready + * it turned out that parasitic capacities are extending the time + * until DOUT has reached it's value + */ + ndelay(hx711_data->data_ready_delay_ns); + val = gpiod_get_value(hx711_data->gpiod_dout); /* * here we are not waiting for 0.2 us as suggested by the datasheet, @@ -120,6 +136,12 @@ static int hx711_cycle(struct hx711_data *hx711_data) gpiod_set_value(hx711_data->gpiod_pd_sck, 0); preempt_enable(); + /* + * make it a square wave for addressing cases with capacitance on + * PC_SCK + */ + ndelay(hx711_data->data_ready_delay_ns); + return val; } @@ -458,6 +480,7 @@ static const struct iio_chan_spec hx711_chan_spec[] = { static int hx711_probe(struct platform_device *pdev) { struct device *dev = &pdev->dev; + struct device_node *np = dev->of_node; struct hx711_data *hx711_data; struct iio_dev *indio_dev; int ret; @@ -530,6 +553,22 @@ static int hx711_probe(struct platform_device *pdev) hx711_data->gain_set = 128; hx711_data->gain_chan_a = 128; + hx711_data->clock_frequency = 400000; + ret = of_property_read_u32(np, "clock-frequency", + &hx711_data->clock_frequency); + + /* + * datasheet says the high level of PD_SCK has a maximum duration + * of 50 microseconds + */ + if (hx711_data->clock_frequency < 20000) { + dev_warn(dev, "clock-frequency too low - assuming 400 kHz\n"); + hx711_data->clock_frequency = 400000; + } + + hx711_data->data_ready_delay_ns = + 1000000000 / hx711_data->clock_frequency; + platform_set_drvdata(pdev, indio_dev); indio_dev->name = "hx711";
On a system with parasitic capacitance it turned out that DOUT is not ready after 100 ns after PD_SCK has raised. A measurement showed almost 1000 ns until DOUT has reached its correct value. With this patch its now possible to wait until data is ready. The wait time should not be higher than the maximum PD_SCK high time which is corresponding to the datasheet 50000 ns. Signed-off-by: Andreas Klinger <ak@it-klinger.de> --- drivers/iio/adc/hx711.c | 39 +++++++++++++++++++++++++++++++++++++++ 1 file changed, 39 insertions(+)