RE: [PATCH 1/8] iio: core: Introduce CALORIES channel type

From: Tirdea, Irina
Date: Sun Jan 11 2015 - 08:44:23 EST

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> -----Original Message-----
> From: Jonathan Cameron [mailto:jic23@xxxxxxxxxx]
> Sent: 01 January, 2015 12:30
> To: Tirdea, Irina; linux-iio@xxxxxxxxxxxxxxx
> Cc: linux-kernel@xxxxxxxxxxxxxxx; Dogaru, Vlad; Baluta, Daniel; Hartmut Knaack; Lars-Peter Clausen; Peter Meerwald
> Subject: Re: [PATCH 1/8] iio: core: Introduce CALORIES channel type
>
> On 29/12/14 14:42, Tirdea, Irina wrote:
> >
> >
> >> -----Original Message-----
> >> From: linux-iio-owner@xxxxxxxxxxxxxxx [mailto:linux-iio-owner@xxxxxxxxxxxxxxx] On Behalf Of Jonathan Cameron
> >> Sent: 26 December, 2014 15:26
> >> To: Tirdea, Irina; linux-iio@xxxxxxxxxxxxxxx
> >> Cc: linux-kernel@xxxxxxxxxxxxxxx; Dogaru, Vlad; Baluta, Daniel; Hartmut Knaack; Lars-Peter Clausen; Peter Meerwald
> >> Subject: Re: [PATCH 1/8] iio: core: Introduce CALORIES channel type
> >>
> >> On 19/12/14 22:57, Irina Tirdea wrote:
> >>> Some devices compute the number of calories that the user has
> >>> burnt since the last reset.
> >>>
> >>> One of this devices is Freescale's MMA9553L
> >>> (http://www.freescale.com/files/sensors/doc/ref_manual/MMA9553LSWRM.pdf)
> >>> that computes the number of calories based on weight and step rate.
> >>>
> >>> Introduce a new channel type CALORIES to export these values.
> >>>
> >>> Signed-off-by: Irina Tirdea <irina.tirdea@xxxxxxxxx>
> >> hmm.. Ideally we use SI units for everything, but in human energy usage
> >> Calories are the most common unit by a long way. I'm having some trouble
> >> even finding the conversion for this particular for of calorie.
> >>
> >
> > Initially I wanted to use the calorie as unit, but it seemed a little bit confusing because there are 2 different units both called calorie:
> > - The small calorie or gram calorie approximates the energy needed to increase the temperature of 1 gram of water by 1 C.
> > - The kilogram calorie or "large calorie" is an obsolete term used for the kilocalorie, which is the calorie used to express the energy
> content of foods. However, in practice, the prefix "kilo" is usually omitted.
> >
> oops. I didn't actually read the patch beyond seeing CALORIES as the type in the title ;)
> > Instead of using cal (small calorie), kcal or Calorie (large calorie) as unit, I think it would be more clear to use Joule since that would
> eliminate confusion and it is also a SI unit.
> >
> > According to the conversion table from here http://physics.nist.gov/Pubs/SP811/appenB9.html#ENERGY, we could convert
> nutritional calories to Joules using the following formula:
> > Energy (Joules) = 4 184 * calories_th_nutrition
> > I used this formula in the implementation of the driver.
> Joules is good, but then the type needs to be ENERGY rather than CALORIES.
> (and in_energy_* etc).

That sounds better. Will change the type to ENERGY.

> >
> >> Now clearly it doesn't matter if the only energy sensors we ever get
> >> are for human activity. However, that's unlikely to be the case. We
> >> already have devices doing instantaneous power and there are plenty
> >> of smart meter chips out there (though of course, they will use the
> >> option of kW Hours just to confuse matters).
> >>
> >> I'd definitely prefer joules if we can do it with out a large amount of
> >> pain.
> >>
> >> Lars - any views on this? (Analog do make plenty of 'energy' measurement
> >> devices after all!)
> >>> ---
> >>> Documentation/ABI/testing/sysfs-bus-iio | 9 +++++++++
> >>> drivers/iio/industrialio-core.c | 1 +
> >>> include/linux/iio/types.h | 1 +
> >>> 3 files changed, 11 insertions(+)
> >>>
> >>> diff --git a/Documentation/ABI/testing/sysfs-bus-iio b/Documentation/ABI/testing/sysfs-bus-iio
> >>> index df5e69e..bb9342b 100644
> >>> --- a/Documentation/ABI/testing/sysfs-bus-iio
> >>> +++ b/Documentation/ABI/testing/sysfs-bus-iio
> >>> @@ -282,6 +282,7 @@ What: /sys/bus/iio/devices/iio:deviceX/in_current_scale
> >>> What: /sys/bus/iio/devices/iio:deviceX/in_accel_scale
> >>> What: /sys/bus/iio/devices/iio:deviceX/in_accel_peak_scale
> >>> What: /sys/bus/iio/devices/iio:deviceX/in_anglvel_scale
> >>> +What: /sys/bus/iio/devices/iio:deviceX/in_calories_scale
> >>> What: /sys/bus/iio/devices/iio:deviceX/in_magn_scale
> >>> What: /sys/bus/iio/devices/iio:deviceX/in_magn_x_scale
> >>> What: /sys/bus/iio/devices/iio:deviceX/in_magn_y_scale
> >>> @@ -1049,6 +1050,14 @@ Description:
> >>> For a list of available output power modes read
> >>> in_accel_power_mode_available.
> >>>
> >>> +What: /sys/.../iio:deviceX/in_calories_input
> >>> +What: /sys/.../iio:deviceX/in_calories_raw
> >>> +KernelVersion: 3.17
> >>> +Contact: linux-iio@xxxxxxxxxxxxxxx
> >>> +Description:
> >>> + This attribute is used to read the number of calories burned since the last
> >>> + reset. Units after application of scale are Joules.
> >>> +
> >>> What: /sys/bus/iio/devices/iio:deviceX/store_eeprom
> >>> KernelVersion: 3.4.0
> >>> Contact: linux-iio@xxxxxxxxxxxxxxx
> >>> diff --git a/drivers/iio/industrialio-core.c b/drivers/iio/industrialio-core.c
> >>> index ee442ee..5d95e84 100644
> >>> --- a/drivers/iio/industrialio-core.c
> >>> +++ b/drivers/iio/industrialio-core.c
> >>> @@ -72,6 +72,7 @@ static const char * const iio_chan_type_name_spec[] = {
> >>> [IIO_HUMIDITYRELATIVE] = "humidityrelative",
> >>> [IIO_ACTIVITY] = "activity",
> >>> [IIO_STEPS] = "steps",
> >>> + [IIO_CALORIES] = "calories",
> >>> };
> >>>
> >>> static const char * const iio_modifier_names[] = {
> >>> diff --git a/include/linux/iio/types.h b/include/linux/iio/types.h
> >>> index 904dcbb..d2fe930 100644
> >>> --- a/include/linux/iio/types.h
> >>> +++ b/include/linux/iio/types.h
> >>> @@ -32,6 +32,7 @@ enum iio_chan_type {
> >>> IIO_HUMIDITYRELATIVE,
> >>> IIO_ACTIVITY,
> >>> IIO_STEPS,
> >>> + IIO_CALORIES,
> >>> };
> >>>
> >>> enum iio_modifier {
> >>>
> >>
> >> --
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