This version (27 Sep 2022 09:31) was approved by Ramona Bolboaca.
Table of Contents
MAX11205 IIO ADC Linux Driver
Supported Devices
Evaluation Boards
Description
The MAX11205 is an ultra-low-power (< 300µA max active current), high-resolution, serial output ADC. This device provides the highest resolution per unit power in the industry and is optimized for applications that require very high dynamic range with low power such as sensors on a 4mA to 20mA industrial control loop. The MAX11205 provides a high-accuracy internal oscillator that requires no external components.
When used with the specified data rates, the internal digital filter provides more than 80dB rejection of 50Hz or 60Hz line noise. The MAX11205 provides a simple 2-wire serial interface in the space-saving, 10-pin µMAX® package. The MAX11205 operates over the -40°C to +85°C temperature range.
Source Code
Status
| Source | Mainlined? |
|---|---|
| git | Accepted, waiting for integration |
Files
| Function | File |
|---|---|
| driver | drivers/iio/adc/max11205.c |
| Documentation | maxim,max11205.yaml |
Driver testing
When configured with channel 0 as voltage output the following structure is created under the corresponding IIO device.
This specifies any shell prompt running on the target
root@analog:/sys/bus/iio/devices# ls iio:device0 iio_sysfs_trigger trigger0 root@analog:/sys/bus/iio/devices# cd iio:device0 root@analog:/sys/bus/iio/devices/iio:device0# ls -l total 0 drwxr-xr-x 2 root root 0 Sep 6 08:17 buffer -r--r--r-- 1 root root 4096 Sep 6 08:17 dev -rw-r--r-- 1 root root 4096 Sep 6 08:17 in_voltage0_raw -rw-r--r-- 1 root root 4096 Sep 6 08:17 in_voltage0_sampling_frequency -rw-r--r-- 1 root root 4096 Sep 6 08:17 in_voltage0_scale -r--r--r-- 1 root root 4096 Sep 6 08:17 name lrwxrwxrwx 1 root root 0 Sep 6 08:17 of_node -> ../../../../../../../../firmware/devicetree/base/soc/spi@7e204000/max11205@0 drwxr-xr-x 2 root root 0 Sep 6 08:17 power drwxr-xr-x 2 root root 0 Sep 6 08:17 scan_elements lrwxrwxrwx 1 root root 0 Sep 6 08:17 subsystem -> ../../../../../../../../bus/iio drwxr-xr-x 2 root root 0 Sep 6 08:17 trigger -rw-r--r-- 1 root root 4096 Sep 6 08:17 uevent
Show device name
This specifies any shell prompt running on the target
root@analog:/sys/bus/iio/devices/iio:device0# cat name max11205a
Show raw measurement
Description:
Raw measurement of voltage on channel 0.
This specifies any shell prompt running on the target
root@analog:/sys/bus/iio/devices/iio:device0# cat in_voltage0_raw 20137
U = in_voltage0_raw * in_voltage0_scale = 20137 * 0.097656250 = 1966.50390625 mV
Show scale
Description:
Scale to be applied to the raw measurement of voltage on channel 0 in order to obtain the actual voltage.
This specifies any shell prompt running on the target
root@analog:/sys/bus/iio/devices/iio:device0# cat in_voltage0_scale 0.097656250
Show sampling frequency
Description:
The sampling frequency of the device.
This specifies any shell prompt running on the target
root@analog:/sys/bus/iio/devices/iio:device0# cat in_voltage0_sampling_frequency 116
Trigger management
This specifies any shell prompt running on the target
root@analog:/sys/bus/iio/devices/iio:device0# cat trigger/current_trigger max11205a-dev0
Buffer management
The Industrial I/O subsystem provides support for various ring buffer based data acquisition methods. Apart from device specific hardware buffer support, the user can chose between two different software ring buffer implementations. One is the IIO lock free software ring, and the other is based on Linux kfifo. Devices with buffer support feature an additional sub-folder in the /sys/bus/iio/devices/deviceX/ folder hierarchy. Called deviceX:bufferY, where Y defaults to 0, for devices with a single 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.
watermark
A single positive integer specifying the maximum number of scan
elements to wait for.
Poll will block until the watermark is reached.
Blocking read will wait until the minimum between the requested
read amount or the low water mark is available.
Non-blocking read will retrieve the available samples from the
buffer even if there are less samples then watermark level. This
allows the application to block on poll with a timeout and read
the available samples after the timeout expires and thus have a
maximum delay guarantee.
data_available
A read-only value indicating the bytes of data available in the
buffer. In the case of an output buffer, this indicates the
amount of empty space available to write data to. In the case of
an input buffer, this indicates the amount of data available for
reading.
length_align_bytes
Using the high-speed interface. DMA buffers may have an alignment requirement for the buffer length.
Newer versions of the kernel will report the alignment requirements
associated with a device through the `length_align_bytes` property.
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@analog:/sys/bus/iio/devices/iio:device0/scan_elements# ls in_voltage0_en in_voltage0_index in_voltage0_type
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/max11205.txt · Last modified: 26 Sep 2022 13:27 by Ramona Bolboaca