LIBIIO

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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Hi Paul,

I didn't read all of your text (will do later), but would like to point out that there is alreay a project going on here:
http://sourceforge.net/projects/iioutils/

You're very welcome to contribute.

Regards,
Manuel Stahl

Am Montag, 3. März 2014, 12:31:46 schrieb Paul Cercueil:

Quoted 101 lines

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.

Quoted 9 lines

Thanks,

Paul

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Quoted 4 lines

Hi Paul,

I didn't read all of your text (will do later), but would like to point out that there is alreay a project going on here:
http://sourceforge.net/projects/iioutils/

Well, the iioutils lib is extremely low level. It is basically just a bunch of fprintfs and fscanfs. The libiio has a more high level abstraction build in. The basic structure of the libiio is the iio_context, it is a (to the user transparent) struct that is used for all operations (E.g. like get_devices()). If an application wants to do something it first allocates a context, there can be multiple contexts per application and each contexts tracks is own state, so there is no globally shared state. Each context has a backed. One backend is the local backend that performs all operations on device the application is running on. But there is also a network backend that connects to a sever running on a different device. This allows to run the same application on local and remote the devices without the application having to have any special code for supporting this.

There is also a IIO daemon that can sit between the application and the IIO sysfs. This daemon allows for multiple applications accessing the same device without trampling over each others feet and also allows to run the application without root rights.

My hopes are that the libiio can eventually replace the iio-utils lib.

Am Mittwoch, 5. März 2014, 15:31:42 schrieb Lars-Peter Clausen:

Quoted 4 lines · Manuel Stahl

Quoted 3 lines

Hi Paul,

I didn't read all of your text (will do later), but would like to point out that

there is alreay a project going on here:

Quoted 14 lines

Quoted 1 line

http://sourceforge.net/projects/iioutils/

Well, the iioutils lib is extremely low level. It is basically just a bunch of fprintfs and fscanfs. The libiio has a more high level abstraction build in. The basic structure of the libiio is the iio_context, it is a (to the user transparent) struct that is used for all operations (E.g. like get_devices()). If an application wants to do something it first allocates a context, there can be multiple contexts per application and each contexts tracks is own state, so there is no globally shared state. Each context has a backed. One backend is the local backend that performs all operations on device the application is running on. But there is also a network backend that connects to a sever running on a different device. This allows to run the same application on local and remote the devices without the

application having to have any special code for supporting this.

Quoted 6 lines

There is also a IIO daemon that can sit between the application and the IIO sysfs. This daemon allows for multiple applications accessing the same device without trampling over each others feet and also allows to run the application without root rights.

Quoted 1 line

My hopes are that the libiio can eventually replace the iio-utils lib.

That's also what I hope for. But we should try to avoid name clashes. The lib in iioutils is also called libiio. So I propose to merge the repositories somehow.

Quoted 4 lines · Manuel Stahl

Hi Paul,

I didn't read all of your text (will do later), but would like to point out that there is alreay a project going on here:
http://sourceforge.net/projects/iioutils/

Well, the iioutils lib is extremely low level. It is basically just a bunch of fprintfs and fscanfs. The libiio has a more high level abstraction build in. The basic structure of the libiio is the iio_context, it is a (to the user transparent) struct that is used for all operations (E.g. like get_devices()). If an application wants to do something it first allocates a context, there can be multiple contexts per application and each contexts tracks is own state, so there is no globally shared state. Each context has a backed. One backend is the local backend that performs all operations on device the application is running on. But there is also a network backend that connects to a sever running on a different device. This allows to run the same application on local and remote the devices without the application having to have any special code for supporting this.

There is also a IIO daemon that can sit between the application and the IIO sysfs. This daemon allows for multiple applications accessing the same device without trampling over each others feet and also allows to run the application without root rights.

My hopes are that the libiio can eventually replace the iio-utils lib.

- Lars

Quoted 123 lines

You're very welcome to contribute.

Regards,
Manuel Stahl

Am Montag, 3. März 2014, 12:31:46 schrieb Paul Cercueil:

Quoted 110 lines

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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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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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

Quoted 115 lines · Paul Cercueil

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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