This version (29 Dec 2020 20:30) was approved by Robin Getz.The Previously approved version (29 Dec 2020 20:29) is available.
Table of Contents
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
| Function | File |
|---|---|
| driver | https://github.com/analogdevicesinc/linux/blob/master/drivers/iio/adc/ad738x.c |
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
- IIO mailing list: linux [dash] iio [at] vger [dot] kernel [dot] org
resources/tools-software/linux-drivers/iio-adc/ad738x.txt · Last modified: 29 Dec 2020 20:30 by Robin Getz