From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from saturn.retrosnub.co.uk ([178.18.118.26]:41567 "EHLO saturn.retrosnub.co.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751141AbbJKOHX (ORCPT ); Sun, 11 Oct 2015 10:07:23 -0400 Subject: Re: [PATCH] vf610_adc: Fix internal temperature calculation To: Duan Andy , Bhuvanchandra DV , "linux-iio@vger.kernel.org" References: <1443015807-17764-1-git-send-email-bhuvanchandra.dv@toradex.com> <560810DD.5030900@kernel.org> <561A6CB7.6010700@kernel.org> Cc: "stefan@agner.ch" , "maitysanchayan@gmail.com" , "knaack.h@gmx.de" , "lars@metafoo.de" , "pmeerw@pmeerw.net" , "shawn.guo@linaro.org" , "linux-kernel@vger.kernel.org" From: Jonathan Cameron Message-ID: <561A6D19.90902@kernel.org> Date: Sun, 11 Oct 2015 15:07:21 +0100 MIME-Version: 1.0 In-Reply-To: <561A6CB7.6010700@kernel.org> Content-Type: text/plain; charset=utf-8 Sender: linux-iio-owner@vger.kernel.org List-Id: linux-iio@vger.kernel.org On 11/10/15 15:05, Jonathan Cameron wrote: > On 08/10/15 03:01, Duan Andy wrote: >> From: Jonathan Cameron Sent: Sunday, September 27, 2015 11:53 PM >>> To: Bhuvanchandra DV; linux-iio@vger.kernel.org >>> Cc: stefan@agner.ch; maitysanchayan@gmail.com; Duan Fugang-B38611; >>> knaack.h@gmx.de; lars@metafoo.de; pmeerw@pmeerw.net; shawn.guo@linaro.org; >>> linux-kernel@vger.kernel.org; Duan Fugang-B38611 >>> Subject: Re: [PATCH] vf610_adc: Fix internal temperature calculation >>> >>> On 23/09/15 14:43, Bhuvanchandra DV wrote: >>>> There is an observed temperature difference of ~20°C with the internal >>>> temperature reading and the temperature measured on SoC package. >>>> Existing calculations consider the typical values provided in >>>> datasheet. Those typical values are valid for VREFH_ADC at 3.0V. >>>> Voltage at 25°C is different for different VREFH_ADC voltages. With >>>> VREFH_ADC at 3.3V, voltage at 25°C is 0.699V. Hence update the VTEMP25 >>>> to 0.699V which gives ADCR@Temp25 as 867 and the final temperature >>>> readings differs with ~5°C from the external readings. >>>> >>>> Formula for finding ADCR@Temp25: >>>> ADCR@Temp25 = (ADCR@Vdd * V@TEMP25 * 10) / VDDconv >>>> >>>> ADCR@Vdd for 12-Bit ADC = 4095 >>>> VDDconv = VREFH_ADC * 10 >>>> >>>> VREFH_ADC@3.3V >>>> ADCR@Temp25 = (4095 * .699 * 10) / 33 >>>> ADCR@Temp25 ~= 867 >>>> >>>> | VREFH_ADC | V@TEMP25 | VDDconv | ADCR@Temp25 | >>>> | 3.0V | 0.696mV | 30 | 950 | >>>> | 3.3V | 0.699mV | 33 | 867 | >>>> >>>> Signed-off-by: Bhuvanchandra DV >>> Looks fine to me, but I'll need an Ack from Fugang on this one as I don't >>> know or have the part I'm afraid. >>> >>> Jonathan >> >> The patch is fine for me. Sorry for the late response due to vacation. >> >> Acked-by: Fugang Duan > Applied to the fixes-togreg branch of iio.git and marked for stable. > Thanks, > Jonathan Actually, change of plan. I'll hold this until Stefan's query is answered. (naughty me - I hadn't read the whole thread!) >> >>>> --- >>>> drivers/iio/adc/vf610_adc.c | 19 ++++++++++++++----- >>>> 1 file changed, 14 insertions(+), 5 deletions(-) >>>> >>>> diff --git a/drivers/iio/adc/vf610_adc.c b/drivers/iio/adc/vf610_adc.c >>>> index f4df2a7..e7abc13 100644 >>>> --- a/drivers/iio/adc/vf610_adc.c >>>> +++ b/drivers/iio/adc/vf610_adc.c >>>> @@ -103,6 +103,13 @@ >>>> >>>> #define DEFAULT_SAMPLE_TIME 1000 >>>> >>>> +/* V at 25°C of 696 mV */ >>>> +#define VF610_VTEMP25_3V0 950 >>>> +/* V at 25°C of 699 mV */ >>>> +#define VF610_VTEMP25_3V3 867 >>>> +/* Typical sensor slope coefficient at all temperatures */ >>>> +#define VF610_TEMP_SLOPE_COEFF 1840 >>>> + >>>> enum clk_sel { >>>> VF610_ADCIOC_BUSCLK_SET, >>>> VF610_ADCIOC_ALTCLK_SET, >>>> @@ -636,11 +643,13 @@ static int vf610_read_raw(struct iio_dev >>> *indio_dev, >>>> break; >>>> case IIO_TEMP: >>>> /* >>>> - * Calculate in degree Celsius times 1000 >>>> - * Using sensor slope of 1.84 mV/°C and >>>> - * V at 25°C of 696 mV >>>> - */ >>>> - *val = 25000 - ((int)info->value - 864) * 1000000 / >>> 1840; >>>> + * Calculate in degree Celsius times 1000 >>>> + * Using the typical sensor slope of 1.84 mV/°C >>>> + * and VREFH_ADC at 3.3V, V at 25°C of 699 mV >>>> + */ >>>> + *val = 25000 - ((int)info->value - VF610_VTEMP25_3V3) * >>>> + 1000000 / VF610_TEMP_SLOPE_COEFF; >>>> + >>>> break; >>>> default: >>>> mutex_unlock(&indio_dev->mlock); >>>> > > -- > 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 >