Hi Jonathan,
About function naming, my convention is to name the API functions after
the structure they work with: iio_device_* accept a iio_device
structure, iio_channel_* accept a iio_channel, iio_context_* accept a
iio_context.
In that logic, the create functions are not passed a iio_context, so
they are not named with the same pattern. However, I really don't mind
to change that if you think having them named iio_context_create_* would
be better.
About attributes sharing, what you describe is already implemented, just
not for all device attributes. Given the following sysfs files:
in_magn_scale
in_magn_x_raw
in_magn_y_raw
in_magn_z_raw
the local backend of the library will detect that 'in_magn_scale' is a
device attribute that should be shared between all input channels named
'magn[0-9]+' or 'magn_{modifier}'. For the 'sampling_frequency'
attribute, the library has no way to tell whether or not it applies to
the channels, and so it is left as a device attribute.
Thanks for your comments!
Paul
On 03/05/2014 06:29 PM, Jonathan Cameron wrote:
Hi Paul
Looks good. I will have a more detailed look at some point.
Just been browsing headers. One trivial point...
Try to keep function naming consistent.
I would expect create functions to be named like
iio_context_xml_create etc rather than iio_create...
Your destroy etc are that way around. Note I actually had a similar mess in early kernel iio interfaces :)
I haven't look in detail but it would be nice to hide some of the complexity of attribute
sharing so if someone queries sampling frequency for a channel, the fact it is
specified for a device is hidden. This might involve one attr appearing in multiple places in your hierarchy. Is this something you
would consider? Write semantics are more complex though.
Also beware that according to the abi, any write to an attribute can change any other
attribute (there are sanity restrictions though)
Just quick thoughts! Sorry for top posting:)
Jonathan
On March 3, 2014 11:31:46 AM GMT+00:00, Paul Cercueil <paul.cercueil@xxxxxxxxxx> wrote:
Hi there,
I would like to present the project I've been working on for the past
two weeks: libiio, a library for interfacing IIO devices.
Available here: https://github.com/analogdevicesinc/libiio
As it is still in its infancy, I would like to receive feedback about
the API, what is good, what would you change etc.
The API provides a couple of top-level functions to create a context,
either bound to the local IIO devices through sysfs, to a XML
representation, or to a remote server. This context structure (struct
iio_context) contains a list of devices and the context-specific
low-level operations to interact with them.
From the context structure it is possible to retrieve the structures
representing the devices (struct iio_device). Devices have an ID, a
name, attributes and channels.
Attributes essentially correspond to files in sysfs. For instance, the
attribute "sampling_frequency" of the device with the ID "iio:device0"
matches the file "/sys/bus/iio/devices/iio:device0/sampling_frequency".
The API provides functions to read or write attributes.
Channels (struct iio_channel) represent a measure channel of a ADC or a
control channel of an DAC. In the local context, the channels are
deduced from the filenames in sysfs. For example, the file
"out_voltage0_vccout_offset" translates to an output channel with ID
"voltage0", name "vccout" featuring an attribute named "offset".
The following sysfs files, for instance, would create the following
tree:
root:/> ls -1 -p /sys/bus/iio/devices/iio:device0
buffer/
dev
...
in_magn_filter_low_pass_3db_frequency
in_magn_scale
in_magn_x_raw
in_magn_y_raw
in_magn_z_raw
name
power/
sampling_frequency
scan_elements/
subsystem
trigger/
uevent
---
IIO context has 1 devices:
iio:device0: adis16488
11 channels found:
...
magn_x: (input)
4 channel-specific attributes found:
attr 0: calibbias
attr 1: filter_low_pass_3db_frequency
attr 2: raw
attr 3: scale
magn_y: (input)
4 channel-specific attributes found:
attr 0: calibbias
attr 1: filter_low_pass_3db_frequency
attr 2: raw
attr 3: scale
magn_z: (input)
4 channel-specific attributes found:
attr 0: calibbias
attr 1: filter_low_pass_3db_frequency
attr 2: raw
attr 3: scale
1 device-specific attributes found:
attr 0: sampling_frequency
---
The API provides ways to read and write a stream of values. Either the
raw stream (basically reading/writing the dev node directly), or a
processed stream, corresponding to a single channel, with an optional
conversion step. In this case, the conversion is automatically deduced
from the attributes, notably the "scale" attribute.
One recurring issue when working with IIO devices, is that only one
application can use an IIO device at a time. I intend to address that
issue by developping a network daemon (called iiod, that's original)
that would use the local backend of the libiio library, and stream the
data from/to a device from/to all of its connected clients. The clients
would then just be applications compiled with the libiio library, and
using the network backend of the library (note that switching between
backends is just a matter of creating the iio_context structure with a
different function). Once that works, a specific daemon / libiio
backend
couple could be designed using fast SHM mechanism for high-speed
concurrent local access to the devices.
As I may be overseeing certain things or missing others, I would like
to
know what is your opinion of the API and the library so far, and if you
would use such a library. The feedback is important to me so that the
project moves in the right direction.
Thanks,
Paul
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