Where Can I Find Good Documentation for IIO Subsystem and IIO Drivers

Hi,

The IIO subsystem is in the Linux kernel for more than 10 years. It's not an Analog Devices thing.

You can find some sort of digitizing products from almost all vendors out there.

There is good documentation, however I agree it is somewhat scattered. 

There are typically two sides - and the questions is always - do you want to become a Linux kernel developer or do you just want to use Linux or IIO devices using their user API?

If you want to understand the IIO subsystem you can start reading here and you find both types of information:

• https://www.kernel.org/doc/html/latest/driver-api/iio/

What you always need to know when using IIO devices are their structure and device/channel attributes and conventions

Please see here: sysfs-bus-iio-*

• https://elixir.bootlin.com/linux/latest/source/Documentation/ABI/testing

If you need to instantiate IIO devices via devicetree you find a description of the required and optional properties here:

• https://elixir.bootlin.com/linux/latest/source/Documentation/devicetree/bindings/iio

In general there are lot's of very good (recorded) presentations about IIO available on the WEB you just need to use your favorite search engine and you'll find lot's of good hits.

To use IIO devices you don't need libiio, however libiio brings you some level of convenience, integration and supports for different environments and ecosystems.

Libiio is not tied to any particular IIO device, it's fully transparent.

if you want to use libiio you can go to the Analog Device Wiki and find some information and you can read the github documentation

• http://analogdevicesinc.github.io/libiio/
• http://analogdevicesinc.github.io/libiio/v0.24/libiio/index.html
• http://analogdevicesinc.github.io/libiio/v0.24/python/index.html
• http://analogdevicesinc.github.io/libiio/v0.24/csharp/index.html
• etc.

Like you said, some IIO devices have different capabilities.

You find IIO devices with or without buffer support. Triggered or self triggered. 

When they have a buffer there can be two types of interfaces a highspeed interface and a low speed interface.

If you then look even closer you find that the transport mechanism can be different.  

Let's get back to your SPI examples.

The Linux kernel frameworks/subsystems offer sometimes alternative APIs, sometimes they offer additional options and flexibilities so sometimes you see  

 spi_write_then_read() when you just need to read and write simultaneously, but if you look closer at the source of this function:

• https://elixir.bootlin.com/linux/latest/source/drivers/spi/spi.c#L4274

You see that it also uses spi_message_init() , spi_message_add_tail(), spi_sync()

Or spi_message_init_with_transfers() for example -

• https://elixir.bootlin.com/linux/latest/source/include/linux/spi/spi.h#L1104

Is just a convenient inline - that does spi_message_init() , spi_message_add_tail()

......etc. 

ddickerhoof said:

Where can I find a good overview of how all the components and APIs play together, so that I have a starting place for putting together a driver with full capabilities for the IIO system?

So you want to be come a kernel developer. Then I would continue looking/studying the sources.

Watching presentations, reading the mailing list archives. Or other vendors wikis such as:

https://wiki.st.com/stm32mpu/wiki/IIO_overview

-Michael

Hi,

The IIO subsystem is in the Linux kernel for more than 10 years. It's not an Analog Devices thing.

You can find some sort of digitizing products from almost all vendors out there.

There is good documentation, however I agree it is somewhat scattered. 

There are typically two sides - and the questions is always - do you want to become a Linux kernel developer or do you just want to use Linux or IIO devices using their user API?

If you want to understand the IIO subsystem you can start reading here and you find both types of information:

• https://www.kernel.org/doc/html/latest/driver-api/iio/

What you always need to know when using IIO devices are their structure and device/channel attributes and conventions

Please see here: sysfs-bus-iio-*

• https://elixir.bootlin.com/linux/latest/source/Documentation/ABI/testing

If you need to instantiate IIO devices via devicetree you find a description of the required and optional properties here:

• https://elixir.bootlin.com/linux/latest/source/Documentation/devicetree/bindings/iio

In general there are lot's of very good (recorded) presentations about IIO available on the WEB you just need to use your favorite search engine and you'll find lot's of good hits.

To use IIO devices you don't need libiio, however libiio brings you some level of convenience, integration and supports for different environments and ecosystems.

Libiio is not tied to any particular IIO device, it's fully transparent.

if you want to use libiio you can go to the Analog Device Wiki and find some information and you can read the github documentation

• http://analogdevicesinc.github.io/libiio/
• http://analogdevicesinc.github.io/libiio/v0.24/libiio/index.html
• http://analogdevicesinc.github.io/libiio/v0.24/python/index.html
• http://analogdevicesinc.github.io/libiio/v0.24/csharp/index.html
• etc.

Like you said, some IIO devices have different capabilities.

You find IIO devices with or without buffer support. Triggered or self triggered. 

When they have a buffer there can be two types of interfaces a highspeed interface and a low speed interface.

If you then look even closer you find that the transport mechanism can be different.  

Let's get back to your SPI examples.

The Linux kernel frameworks/subsystems offer sometimes alternative APIs, sometimes they offer additional options and flexibilities so sometimes you see  

 spi_write_then_read() when you just need to read and write simultaneously, but if you look closer at the source of this function:

• https://elixir.bootlin.com/linux/latest/source/drivers/spi/spi.c#L4274

You see that it also uses spi_message_init() , spi_message_add_tail(), spi_sync()

Or spi_message_init_with_transfers() for example -

• https://elixir.bootlin.com/linux/latest/source/include/linux/spi/spi.h#L1104

Is just a convenient inline - that does spi_message_init() , spi_message_add_tail()

......etc. 

ddickerhoof said:

Where can I find a good overview of how all the components and APIs play together, so that I have a starting place for putting together a driver with full capabilities for the IIO system?

So you want to be come a kernel developer. Then I would continue looking/studying the sources.

Watching presentations, reading the mailing list archives. Or other vendors wikis such as:

https://wiki.st.com/stm32mpu/wiki/IIO_overview

-Michael