This version (26 Oct 2023 09:27) was approved by Kim Seer Paller.The Previously approved version (27 Jul 2023 05:06) is available.
Table of Contents
LTC2358 16-/18-bit, Buffered Octal, IIO SAR ADC Linux Driver
The LTC2358/LTC2357/LTC2353 are low noise, high speed, 16-/18-bit successive approximation register (SAR) ADCs with integrated front end buffers. These ADCs accept a wide common mode range. Pico-amp inputs and high CMRR enable these ADCs to connect directly to a wide range of sensors without compromising measurement accuracy. The demo manual refers to the LTC2358-18 but applies to all parts in the family, the only differences being the number of bits, number of channels and the maximum sample rate. The LTC2358-18 has a flexible SoftSpan™ interface that allows conversion-by-conversion control of the input voltage span on a per-channel basis. An internal 2.048V reference and 2X buffer simplify basic operation while an external reference can be used to increase the input range and the SNR of the ADC.
Supported Devices
This driver supports the
Evaluation Boards
Description
This is a Linux industrial I/O (IIO) subsystem driver, targeting single 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 | master/drivers/iio/adc/ltc2358.c |
| devicetree bindings | Documentation/devicetree/bindings/iio/adc/adi,ltc2358.yaml |
Related Device Drivers
| Function | File |
|---|---|
| driver | drivers/iio/adc/cf_axi_adc_core.c |
| include | drivers/iio/adc/cf_axi_adc.h |
| hdl | DC2677A |
Example Linux Device-Tree Initialization
The LTC2358 driver is a spi-bus driver and can currently only be instantiated via device tree.
Required properties:
- compatible: Must be one of “adi,ltc2358-18”.
- reg: SPI chip select number for the device
- #address-cells: Must be set to 1
- #size-cells: Must be set to 0
- clocks: define reference clock See Documentation/devicetree/bindings/clock/clock-bindings.txt
- clock-names: See Documentation/devicetree/bindings/clock/clock-bindings.txt
- pwms: define PWM generator controller See Documentation/devicetree/bindings/clock/clock-bindings.txt
- pwm-names: See Documentation/devicetree/bindings/clock/clock-bindings.txt
- spi-max-frequency: See Documentation/devicetree/bindings/spi/spi-bus.txt
Optional properties:
- adi,softspan-code:: Number configuration to set ADC input range. The input range is set by the following formula:
- 1: 0V to 1.25V * Vref
- 2: ±1.25V * Vref / 1.024
- 3: ±1.25V * Vref
- 4: 0V to 2.5V * Vref / 1.024
- 5: 0V to 2.5V * Vref
- 6: ±2.5V * Vref / 1.024
- 7: ±2.5V * Vref
Example:
&spi0 {
status = "okay";
ltc2358: adc@0 {
compatible = "adi,ltc2358-18";
reg = <0>;
spi-max-frequency = <1000000>;
#address-cells = <1>;
#size-cells = <0>;
clocks = <&sys_clk>;
clock-names = "clkin";
pwms = <&axi_pwm_gen 0 0>;
pwm-names = "cnv";
channel@0 {
reg = <0>;
adi,softspan-code = <1>;
};
channel@1 {
reg = <1>;
adi,softspan-code = <1>;
};
channel@2 {
reg = <2>;
adi,softspan-code = <2>;
};
channel@3 {
reg = <3>;
adi,softspan-code = <2>;
};
channel@4 {
reg = <4>;
adi,softspan-code = <3>;
};
channel@5 {
reg = <5>;
adi,softspan-code = <4>;
};
channel@6 {
reg = <6>;
adi,softspan-code = <5>;
};
channel@7 {
reg = <7>;
adi,softspan-code = <7>;
};
};
};
| Function | File |
|---|---|
| DC2677A Device Tree | socfpga_cyclone5_sockit_dc2677a.dts |
Enabling Linux driver support
Configure kernel with “make menuconfig” (alternatively use “make xconfig” or “make qconfig”)
The LTC2358 driver depends on PWM and SPI
Linux Kernel Configuration
Device Drivers --->
<*> Industrial I/O support --->
--- Industrial I/O support
-*- Enable ring buffer support within IIO
-*- Industrial I/O lock free software ring
-*- Enable triggered sampling support
*** Analog to digital converters ***
[--snip--]
-*- Analog Devices High-Speed AXI ADC driver core
<*> Analog Devices LTC2358 ADC driver
[--snip--]
*** Pulse-Width Modulation (PWM) Support ***
[--snip--]
<*> Analog Devices AXI PWM generator
[--snip--]
Driver testing / API
Each and every IIO device, typically a hardware chip, has a device folder under /sys/bus/iio/devices/iio:deviceX. Where X is the IIO index of the device. Under every of these directory folders reside a set of files, depending on the characteristics and features of the hardware device in question. These files are consistently generalized and documented in the IIO ABI documentation. In order to determine which IIO deviceX corresponds to which hardware device, the user can read the name file /sys/bus/iio/devices/iio:deviceX/name. In case the sequence in which the iio device drivers are loaded/registered is constant, the numbering is constant and may be known in advance.
This device can be found under /sys/bus/iio/devices/
root:/> cd /sys/bus/iio/devices/ root:/sys/bus/iio/devices> ls iio:device0 iio:device1 root:/sys/bus/iio/devices> cd iio:device0 root:/sys/bus/iio/devices/iio:device0# ls -l drwxr-xr-x 2 root root 0 Apr 2 23:44 buffer -r--r--r-- 1 root root 4096 Apr 2 23:44 dev -rw-r--r-- 1 root root 4096 Apr 2 23:44 in_voltage0_raw -rw-r--r-- 1 root root 4096 Apr 2 23:44 in_voltage0_scale -rw-r--r-- 1 root root 4096 Apr 2 23:44 in_voltage1_raw -rw-r--r-- 1 root root 4096 Apr 2 23:44 in_voltage1_scale -rw-r--r-- 1 root root 4096 Apr 2 23:44 in_voltage2_raw -rw-r--r-- 1 root root 4096 Apr 2 23:44 in_voltage2_scale -rw-r--r-- 1 root root 4096 Apr 2 23:44 in_voltage3_raw -rw-r--r-- 1 root root 4096 Apr 2 23:44 in_voltage3_scale -rw-r--r-- 1 root root 4096 Apr 2 23:44 in_voltage4_raw -rw-r--r-- 1 root root 4096 Apr 2 23:44 in_voltage4_scale -rw-r--r-- 1 root root 4096 Apr 2 23:44 in_voltage5_raw -rw-r--r-- 1 root root 4096 Apr 2 23:44 in_voltage5_scale -rw-r--r-- 1 root root 4096 Apr 2 23:44 in_voltage6_raw -rw-r--r-- 1 root root 4096 Apr 2 23:44 in_voltage6_scale -rw-r--r-- 1 root root 4096 Apr 2 23:44 in_voltage7_raw -rw-r--r-- 1 root root 4096 Apr 2 23:44 in_voltage7_scale -r--r--r-- 1 root root 4096 Apr 2 23:44 name lrwxrwxrwx 1 root root 0 Apr 2 23:44 of_node -> ../../../../../../../firmware/devicetree/base/soc/bridge@c0000000/bridge@100100000/axi-ltc235x@20000 drwxr-xr-x 2 root root 0 Apr 2 23:44 power -rw-r--r-- 1 root root 4096 Apr 2 23:44 sampling_frequency drwxr-xr-x 2 root root 0 Apr 2 23:44 scan_elements lrwxrwxrwx 1 root root 0 Apr 2 23:44 subsystem -> ../../../../../../../bus/iio -rw-r--r-- 1 root root 4096 Apr 2 23:44 sync_start_enable -r--r--r-- 1 root root 4096 Apr 2 23:44 sync_start_enable_available -rw-r--r-- 1 root root 4096 Apr 2 23:44 uevent root:/sys/bus/iio/devices/iio:device0#
Show device name
root:/sys/bus/iio/devices/iio:device0> cat name axi-ltc235x
Show channel scale
Scale to be applied to in_voltagex_raw in order to obtain the measured voltage in millivolts.
root:/sys/bus/iio/devices/iio:device0> cat in_voltage0_scale 0.015625000
Show channel measurement
Raw unscaled voltage measurement on the channel
root:/sys/bus/iio/devices/iio:device0> cat in_voltage0_raw 96352
U = in_voltage0_raw * in_voltage0_scale = 96352 * 0.015625000 = 1505.50 mV
Sampling frequency
The LTC2358 ADC driver supports a variable sampling rate, that can be configured dependent on the number of channels.
See current sampling rate:
root@analog:/sys/bus/iio/devices/iio:device0# cat sampling_frequency 100000
Change the sampling rate:
root@analog:/sys/bus/iio/devices/iio:device0# echo 200000 > sampling_frequency root@analog:/sys/bus/iio/devices/iio:device0# cat sampling_frequency 2000000
Buffer management
Every buffer implementation features a set of files:
root:/sys/bus/iio/devices/iio:device0/buffer> ls -l -r--r--r-- 1 root root 4096 Apr 2 23:50 data_available -rw-r--r-- 1 root root 4096 Apr 2 23:50 enable -rw-r--r-- 1 root root 4096 Apr 2 23:50 length -r--r--r-- 1 root root 4096 Apr 2 23:50 length_align_bytes -r--r--r-- 1 root root 4096 Apr 2 23:50 watermark root:/sys/bus/iio/devices/iio:device0/buffer>
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.
root:/sys/bus/iio/devices/iio:device0/buffer> ls -l -rw-r--r-- 1 root root 4096 Apr 2 23:50 in_voltage0_en -r--r--r-- 1 root root 4096 Apr 2 23:50 in_voltage0_index -r--r--r-- 1 root root 4096 Apr 2 23:50 in_voltage0_type -rw-r--r-- 1 root root 4096 Apr 2 23:50 in_voltage1_en -r--r--r-- 1 root root 4096 Apr 2 23:50 in_voltage1_index -r--r--r-- 1 root root 4096 Apr 2 23:50 in_voltage1_type -rw-r--r-- 1 root root 4096 Apr 2 23:50 in_voltage2_en -r--r--r-- 1 root root 4096 Apr 2 23:50 in_voltage2_index -r--r--r-- 1 root root 4096 Apr 2 23:50 in_voltage2_type -rw-r--r-- 1 root root 4096 Apr 2 23:50 in_voltage3_en -r--r--r-- 1 root root 4096 Apr 2 23:50 in_voltage3_index -r--r--r-- 1 root root 4096 Apr 2 23:50 in_voltage3_type -rw-r--r-- 1 root root 4096 Apr 2 23:50 in_voltage4_en -r--r--r-- 1 root root 4096 Apr 2 23:50 in_voltage4_index -r--r--r-- 1 root root 4096 Apr 2 23:50 in_voltage4_type -rw-r--r-- 1 root root 4096 Apr 2 23:50 in_voltage5_en -r--r--r-- 1 root root 4096 Apr 2 23:50 in_voltage5_index -r--r--r-- 1 root root 4096 Apr 2 23:50 in_voltage5_type -rw-r--r-- 1 root root 4096 Apr 2 23:50 in_voltage6_en -r--r--r-- 1 root root 4096 Apr 2 23:50 in_voltage6_index -r--r--r-- 1 root root 4096 Apr 2 23:50 in_voltage6_type -rw-r--r-- 1 root root 4096 Apr 2 23:50 in_voltage7_en -r--r--r-- 1 root root 4096 Apr 2 23:50 in_voltage7_index -r--r--r-- 1 root root 4096 Apr 2 23:50 in_voltage7_type root:/sys/bus/iio/devices/iio:device0/buffer>
Enable and read 400 samples from both channels:
root@analog:/sys/bus/iio/devices/iio:device0# echo 1 > scan_elements/in_voltage0_en root@analog:/sys/bus/iio/devices/iio:device0# echo 400 > buffer/length root@analog:/sys/bus/iio/devices/iio:device0# echo 1 > buffer/enable root@analog:/sys/bus/iio/devices/iio:device0# hexdump -n 400 /dev/iio\:device0 0000000 e942 000d 0011 0000 afaf 000d 0029 0000 0000010 753b 000d fff5 00ff 39fa 000d 0018 0000 0000020 013e 000d 0017 0000 c776 000c fff4 00ff 0000030 8e84 000c 0017 0000 55d4 000c 0052 0000 0000040 1dab 000c 000b 0000 e5b9 000b 0049 0000 0000050 ab19 000b 0013 0000 6f56 000b 0035 0000 0000060 3470 000b 0020 0000 f9a1 000a 0037 0000 0000070 bcc1 000a 0003 0000 7f89 000a 000d 0000 0000080 4458 000a 0003 0000 0978 000a 000d 0000 0000090 cea9 0009 0041 0000 9551 0009 fff2 00ff 00000a0 5b80 0009 fff1 00ff 210c 0009 0015 0000 00000b0 e486 0008 ffe8 00ff a8d1 0008 ffec 00ff 00000c0 6e13 0008 004e 0000 33a0 0008 001a 0000 00000d0 f7df 0007 fffd 00ff bba2 0007 fffd 00ff 00000e0 7ead 0007 fffe 00ff 43e0 0007 0041 0000 00000f0 08a8 0007 0023 0000 cc9c 0006 ffed 00ff 0000100 9031 0006 001c 0000 5370 0006 fff6 00ff 0000110 1721 0006 0040 0000 dcec 0005 ffe5 00ff 0000120 9ffc 0005 000d 0000 61f3 0005 0016 0000 0000130 247d 0005 0023 0000 e55d 0004 0006 0000 0000140 a725 0004 000e 0000 6d7b 0004 0045 0000 0000150 32e4 0004 ffaa 00ff f77e 0003 ffca 00ff 0000160 bc75 0003 0036 0000 809d 0003 0019 0000 0000170 4582 0003 ffe1 00ff 0921 0003 ffdf 00ff 0000180 c9a5 0002 ffd1 00ff 8a1c 0002 0015 0000 0000190 root@analog:/sys/bus/iio/devices/iio:device0/# echo 0 > buffer/enable
Debug mode
You can write and read the ADC registers using debugfs. Here we will read the configuration number for softspan code set in channel 0.
First go to the device debug folder:
root@analog# cd /sys/kernel/debug/iio/iio:device0
Read the 0x0440 register:
root@analog:/sys/kernel/debug/iio/iio:device0# echo 0x0440 > direct_reg_access root@analog:/sys/kernel/debug/iio/iio:device0# cat direct_reg_access 0x1
More Information
- IIO mailing list: linux [dash] iio [at] vger [dot] kernel [dot] org
resources/tools-software/linux-drivers/iio-adc/ltc2358.txt · Last modified: 26 Oct 2023 09:27 by Kim Seer Paller