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This version (17 Oct 2018 15:43) was approved by spopa.The Previously approved version (19 Jan 2018 10:19) is available.Diff

AD738x IIO Dual Channel Serial ADC Linux Driver

Supported Devices

Evaluation Boards

Description

This is a Linux industrial I/O (IIO) subsystem driver, targeting dual or quad channel serial interface ADCs. The industrial I/O subsystem provides a unified framework for drivers for many different types of converters and sensors using a number of different physical interfaces (i2c, spi, etc). See IIO for more information.

Source Code

Status

Source Mainlined?
git [No]

Files

Devicetree

Required devicetree properties:

  • compatible: Needs to be the name of the device. E.g. “ad7380”
  • reg: The chipselect number used for the device
  • spi-max-frequency: Maximum SPI clock frequency.
  • spi-cpol: Needs to be set for the correct SPI mode
  • vref-supply: Phandle to the fixed regulator
        adc_vref: fixedregulator@0 {
	        compatible = "regulator-fixed";
		regulator-name = "fixed-supply";
		regulator-min-microvolt = <2500000>;
		regulator-max-microvolt = <2500000>;
		regulator-boot-on;
	};

	#address-cells = <1>;
	#size-cells = <0>;
	status = "okay";

	ad738x@0 {
		compatible = "ad7380";
		reg = <0>;
		spi-max-frequency = <1000000>;
		spi-cpol;
		vref-supply = <&adc_vref>;
	};

Driver testing

This specifies any shell prompt running on the target

root:/> cd /sys/bus/iio/devices/
root:/sys/bus/iio/devices> ls
iio:device0

root:/sys/bus/iio/devices> cd iio\:device0

root:/sys/bus/iio/devices/iio:device0> ls -l
drwxr-xr-x 2 root root    0 Sep 12 20:11 buffer
-r--r--r-- 1 root root 4096 Sep 12 20:11 dev
-rw-r--r-- 1 root root 4096 Sep 12 20:11 in_voltage0_raw
-rw-r--r-- 1 root root 4096 Sep 12 20:11 in_voltage1_raw
-rw-r--r-- 1 root root 4096 Sep 12 20:11 in_voltage_scale
-r--r--r-- 1 root root 4096 Sep 12 20:11 name
lrwxrwxrwx 1 root root    0 Sep 12 20:11 of_node -> ../../../../../../../../firmware/devicetree/base/soc/spi@7e204000/ad738x@0
drwxr-xr-x 2 root root    0 Sep 12 20:11 power
drwxr-xr-x 2 root root    0 Sep 12 20:11 scan_elements
lrwxrwxrwx 1 root root    0 Sep 12 20:11 subsystem -> ../../../../../../../../bus/iio
drwxr-xr-x 2 root root    0 Sep 12 20:11 trigger
-rw-r--r-- 1 root root 4096 Sep 12 20:11 uevent

Show device name

This specifies any shell prompt running on the target

root:/sys/bus/iio/devices/iio:device0> cat name
ad7380

Show scale

Description:
scale to be applied to in_voltage0_raw in order to obtain the measured voltage in millivolts.

This specifies any shell prompt running on the target

root:/sys/bus/iio/devices/iio:device0> cat in_voltage_scale
0.076293945

Show channel 0 measurement

Description:
Raw unscaled voltage measurement on channel 0

This specifies any shell prompt running on the target

root:/sys/bus/iio/devices/iio:device0> cat in_voltage0_raw
28583

U = in_voltage0_raw * in_voltage_scale = 28583 * 0.076293945 = 2180.70 mV

Trigger management

If deviceX supports triggered sampling, it’s a so called trigger consumer and there will be an additional folder /sys/bus/iio/device/iio:deviceX/trigger. In this folder there is a file called current_trigger, allowing controlling and viewing the current trigger source connected to deviceX. Available trigger sources can be identified by reading the name file /sys/bus/iio/devices/triggerY/name. The same trigger source can connect to multiple devices, so a single trigger may initialize data capture or reading from a number of sensors, converters, etc.

This driver uses high resolution timers as interrupt source

Description:
Hrtimer triggers creation and destruction

Loading iio-trig-hrtimer module will register hrtimer trigger types allowing users to create hrtimer triggers:

This specifies any shell prompt running on the target

root:/sys/kernel/config/iio/triggers/hrtimer/> mkdir trigger0

Description:
Read name of trigger0

This specifies any shell prompt running on the target

root:/sys/bus/iio/devices/trigger0/> cat name
trigger0

Description:
Configure the sampling frequency of trigger0

This specifies any shell prompt running on the target

root:/sys/bus/iio/devices/trigger0/> echo 500 > sampling_frequency
trigger0

Description:
Make trigger0 to current trigger of device0

This specifies any shell prompt running on the target

root:/sys/bus/iio/devices/iio:device0/> echo trigger0 > trigger/current_trigger 

Description:
Read current trigger source of device0

This specifies any shell prompt running on the target

root:/sys/bus/iio/devices/iio:device0/trigger> cat current_trigger
trigger0 

Buffer management

This specifies any shell prompt running on the target

root:/sys/bus/iio/devices/iio:device0/buffer> ls
enable          length                   watermark
root:/sys/bus/iio/devices/iio:device0/buffer>

Every buffer implementation features a set of files:

length
Get/set the number of sample sets that may be held by the buffer.

enable
Enables/disables the buffer. This file should be written last, after length and selection of scan elements

scan_elements
The scan_elements directory contains interfaces for elements that will be captured for a single triggered sample set in the buffer.

This specifies any shell prompt running on the target

root:/sys/bus/iio/devices/iio:device0/scan_elements> ls 
in_voltage0_en	in_voltage0_index  in_voltage0_type  in_voltage1_en  in_voltage1_index	in_voltage1_type
root:/sys/bus/iio/devices/iio:device0/scan_elements>

in_voltageX_en / in_voltageX-voltageY_en / timestamp_en:
Scan element control for triggered data capture. Writing 1 will enable the scan element, writing 0 will disable it

in_voltageX_type / in_voltageX-voltageY_type / timestamp_type:
Description of the scan element data storage within the buffer and therefore in the form in which it is read from user-space. Form is [s|u]bits/storage-bits. s or u specifies if signed (2's complement) or unsigned. bits is the number of bits of data and storage-bits is the space (after padding) that it occupies in the buffer. Note that some devices will have additional information in the unused bits so to get a clean value, the bits value must be used to mask the buffer output value appropriately. The storage-bits value also specifies the data alignment. So u12/16 will be a unsigned 12 bit integer stored in a 16 bit location aligned to a 16 bit boundary. For other storage combinations this attribute will be extended appropriately.

in_voltageX_index / in_voltageX-voltageY_index / timestamp_index:
A single positive integer specifying the position of this scan element in the buffer. Note these are not dependent on what is enabled and may not be contiguous. Thus for user-space to establish the full layout these must be used in conjunction with all _en attributes to establish which channels are present, and the relevant _type attributes to establish the data storage format.

More Information

resources/tools-software/linux-drivers/iio-adc/ad738x.txt · Last modified: 17 Oct 2018 15:43 by spopa