On 5/8/2012 3:48 PM, Michael Hennerich wrote:
On 05/08/2012 03:32 PM, Jonathan Cameron wrote:
On 5/8/2012 2:26 PM, Hennerich, Michael wrote:
Jonathan Cameron wrote on 2012-05-08:
On 5/7/2012 4:17 PM, Michael Hennerich wrote:
On 05/07/2012 05:00 PM, Michael Hennerich wrote:
On 03/22/2012 10:10 AM, Jonathan Cameron wrote:
On 3/22/2012 8:52 AM, Michael Hennerich wrote:
On 03/21/2012 08:34 PM, Jonathan Cameron wrote:
On 02/22/2012 12:36 PM, michael.hennerich@xxxxxxxxxx wrote:
From: Michael Hennerich<michael.hennerich@xxxxxxxxxx>
Sorry for the slow response on this one. Been off sick...
Anyhow, I'm still not sure what the right interface for this type
of device is.
The obvious options are:
1) Make gain an IIO type (doesn't make much sense as gain is only
going
to be of one particular existing type).
2) Have it as an IIO_ALTVOLTAGE channel as you have here and use
extend
name. Any real reason for picking altvoltage rather than
voltage?
I'm open for advice. Since I made the amplifier being an OUT type
device
I chose IIO_ALTVOLTAGE analogous to our DDS/PLL drivers.
Some VGAs/PGAs work from DC, but typically VGAs are HF devices.
Hmm.. Don't suppose it really matters but we ought to aim for
consistency
(by review) at least. This particular part is DC through to
600MHz.
Clearly gain has the same meaning in either case (assuming it's
linear). 3) Make a change to core to allow a channel to have
elements in info_mask but not actually to have a raw access. Not
entirely sure how we will do that cleanly. Also it's not clear
whether the gain would be an IN or an OUT channel type!
Well - having the ability for channels without raw access element
would be of interest.
True enough. Cleanest way to do this that I can think of is to
make
a tree wide change to add the raw element to the info_mask. We
could
allow for a zero info_mask value actually being the equivalent of
having only a raw channel. It's invasive but if we agreee it
should
be done now is probably the best time to do it (just post merge
window etc).
Hi Jonathan,
Thanks for getting this in place.
Whilst here, we clearly need way of destinguishing values in DB
from
linear gains. Could add a new return type for read_raw callbacks?
Does something like this work for you?
Also wondering if we should introduce IIO_CHAN_INFO_GAIN
for amplifier type devices?
Thinking about it a bit more - why not have iio_chan_type:IIO_GAIN?
Lack of consistency with other devices. If we have a pga on the front
of an adc then the type is voltage and control is done via relevant
info
element. How is this any different?
Well there can be several types of amplifiers voltage, current or
none-electronic
such as optical amplifiers.
Quite. But a given amplier only does one type. Hence arguement still
stands... The only
exception is an analog device such as an accelerometer wired up to a
conventional adc,
but then we don't handle that anyway...
The key element GAIN of an amplifier is only the ratio between input
and output.
The unit cancels out, so why bother with voltage or current?
Far as I know you can't use a voltage amplifier for current
amplificiation or the other way around,
so still makes sence to keep them alongside the type. The voltage vs
altvoltage is a bit of
a pain but I guess no cunning plan is perfect..
It really depends on the external circuit.
But I agree programmable current amplifiers are rare.
More overlap is between IIO_VOLTAGE and IIO_POWER.
Fair point... Whilst there is an issue here, i'm still unconvinced that
an IIO_GAIN type makes sense..
That's why I proposed IIO_GAIN.
Anyways I'm fine with IIO_VOLTAGE for now, but I would like to use
IIO_CHAN_INFO_GAIN
and not IIO_CHAN_INFO_SCALE?
Its internally applied so actually IIO_CHAN_INFO_CALIBSCALE is the
relevant one.
I'm really keen to stick to the existing ones purely because this does
look exactly like a
pga front end as found on numerous adcs. Why treat it differently just
because it is
in a different package? We may need to be clever about routing between
parts sometime
in the future but would be best to keep it simple for now?
I know it's important to stay consistent.
But when talking about characteristics of an amplifier -
CALIBSCALE doesn't really sound well and SCALE is for sure not
applicable.
What /sys/bus/iio/devices/iio:deviceX/in_voltageY_calibscale
Description:
Hardware applied calibration scale factor. (assumed to fix
production inaccuracies). If shared across all channels,
<type>_calibscale is used.
Apart from 'calibration' and 'production inaccuracies' -
Technically seen it does the right thing.
But you need some imagination to use CALIBSCALE for gain.
Perhaps we can rename this? Maybe hardwaregain or
something like that? Can always allow both for a bit and
do a smooth transition over to the new choice?
Jonathan
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