This version (26 Jan 2024 14:29) was approved by Michael Hennerich.The Previously approved version (26 Jan 2024 14:14) is available.
Table of Contents
LTC2664 IIO DAC Linux Driver
The LTC2664 is a family of four-channel, 16-/12-bit ±10V digital-to-analog converters with integrated precision references. They are guaranteed monotonic and have built-in rail-to-rail output buffers. These SoftSpan™ DACs offer five output ranges up to ±10V. The range of each channel is independently programmable, or the part can be hardware-configured for operation in a fixed range.
The integrated 2.5V reference is buffered separately to each channel; an external reference can be used for additional range options. The LTC2664 also includes A/B toggle capability via a dedicated pin or software toggle command.
The SPI/Microwire-compatible 3-wire serial interface operates on logic levels as low as 1.71V at clock rates up to 50MHz.
Supported Devices
Evaluation Boards
Description
This is a Linux industrial I/O (IIO) subsystem driver, targeting single-channel serial interface DACs. 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
Files
| Function | File |
|---|---|
| driver | master?drivers/iio/dac/ltc2664.c |
| dt-bindings | master?Documentation/devicetree/bindings/iio/dac/adi,ltc2664.yaml |
Example platform device initialization
Devicetree
Required devicetree properties:
compatible: Needs to be “adi,” followed by the name of the device. E.g. “adi,ltc2664”reg: The chipselect number used for the devicespi-max-frequency: Maximum SPI clock frequencyVdd-supply: VDD voltage supply regulatoriovcc-supply: Digital Input/Output Supply Voltage.adi,manual-span-operation-config:- Channel nodes with
reg,adi,manual-span-operation-configand optionallyadi,toggle-modeproperties.
Optional devicetree properties:
vref-supply: external reference voltage supply regulator. This should only be set if there is an external reference voltage connected to the REF pin.
adi,manual-span-operation-config:
description:
This property must mimic the MSPAN pin configurations.
By tying the MSPAN pins (MSP2, MSP1 and MSP0) to GND
and/or VCC, any output range can be hardware-configured
with different mid-scale or zero-scale reset options.
The driver needs to be aware of this HW configuration
latched during power on reset for proper operation.
0 - MPS2=GND, MPS1=GND, MSP0=GND
1 - MPS2=GND, MPS1=GND, MSP0=VCC
2 - MPS2=GND, MPS1=VCC, MSP0=GND
3 - MPS2=GND, MPS1=VCC, MSP0=VCC
4 - MPS2=VCC, MPS1=GND, MSP0=GND
5 - MPS2=VCC, MPS1=GND, MSP0=VCC
6 - MPS2=VCC, MPS1=VCC, MSP0=GND
7 - MPS2=VCC, MPS1=VCC, MSP0=VCC (enables SoftSpan feature)
&{/} {
vcc: fixedregulator@1 {
compatible = "regulator-fixed";
regulator-name = "vcc-supply";
regulator-min-microvolt = <5000000>;
regulator-max-microvolt = <5000000>;
};
};
&spi0 {
#address-cells = <1>;
#size-cells = <0>;
status = "okay";
ltc2688: ltc2688@0 {
compatible = "adi,ltc2664";
reg = <0>;
spi-max-frequency = <5000000>;
#address-cells = <1>;
#size-cells = <0>;
vcc-supply = <&vcc>;
iovcc-supply = <&vcc>;
adi,manual-span-operation-config = <7>;
channel@0 {
reg = <0>;
adi,output-range-microvolt = <(-10000000) 10000000>;
};
channel@1 {
reg = <1>;
adi,output-range-microvolt = <(-10000000) 10000000>;
adi,toggle-mode;
};
channel@2 {
reg = <2>;
adi,output-range-microvolt = <(-10000000) 10000000>;
};
channel@3 {
reg = <3>;
adi,output-range-microvolt = <(-10000000) 10000000>;
};
};
};
Driver testing
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 specifies any shell prompt running on the target
root@analog:/> cd /sys/bus/iio/devices/ root@analog:/sys/bus/iio/devices> ls iio:device0 root@analog:/sys/bus/iio/devices> cd iio\:device0 root@analog:/sys/bus/iio/devices/iio:device0> ls -l total 0 drwxr-xr-x 3 root root 0 Jan 25 16:17 . drwxr-xr-x 5 root root 0 Jan 25 16:17 .. -r--r--r-- 1 root root 4096 Jan 25 16:17 name lrwxrwxrwx 1 root root 0 Jan 25 16:17 of_node -> ../../../../../../../../firmware/devicetree/base/soc/spi@7e204000/ltc2688@0 -rw-r--r-- 1 root root 4096 Jan 25 16:17 out_voltage0_offset -rw-r--r-- 1 root root 4096 Jan 26 09:59 out_voltage0_powerdown -rw-r--r-- 1 root root 4096 Jan 26 10:18 out_voltage0_raw -r--r--r-- 1 root root 4096 Jan 25 16:17 out_voltage0_raw_available -rw-r--r-- 1 root root 4096 Jan 25 16:17 out_voltage0_scale -rw-r--r-- 1 root root 4096 Jan 25 16:17 out_voltage1_offset -rw-r--r-- 1 root root 4096 Jan 25 16:17 out_voltage1_powerdown -rw-r--r-- 1 root root 4096 Jan 26 10:18 out_voltage1_raw0 -rw-r--r-- 1 root root 4096 Jan 26 10:18 out_voltage1_raw1 -r--r--r-- 1 root root 4096 Jan 25 16:17 out_voltage1_raw_available -rw-r--r-- 1 root root 4096 Jan 25 16:17 out_voltage1_scale -rw-r--r-- 1 root root 4096 Jan 25 16:17 out_voltage1_symbol -rw-r--r-- 1 root root 4096 Jan 25 16:17 out_voltage1_toggle_en -rw-r--r-- 1 root root 4096 Jan 25 16:17 out_voltage2_offset -rw-r--r-- 1 root root 4096 Jan 25 16:17 out_voltage2_powerdown -rw-r--r-- 1 root root 4096 Jan 26 10:18 out_voltage2_raw -r--r--r-- 1 root root 4096 Jan 25 16:17 out_voltage2_raw_available -rw-r--r-- 1 root root 4096 Jan 25 16:17 out_voltage2_scale -rw-r--r-- 1 root root 4096 Jan 25 16:17 out_voltage3_offset -rw-r--r-- 1 root root 4096 Jan 25 16:17 out_voltage3_powerdown -rw-r--r-- 1 root root 4096 Jan 26 10:18 out_voltage3_raw -r--r--r-- 1 root root 4096 Jan 25 16:17 out_voltage3_raw_available -rw-r--r-- 1 root root 4096 Jan 25 16:17 out_voltage3_scale drwxr-xr-x 2 root root 0 Jan 25 16:17 power lrwxrwxrwx 1 root root 0 Jan 25 16:17 subsystem -> ../../../../../../../../bus/iio -rw-r--r-- 1 root root 4096 Jan 25 16:17 uevent -r--r--r-- 1 root root 4096 Jan 25 16:17 waiting_for_supplier root@analog:/sys/bus/iio/devices/iio:device0#
This specifies any shell prompt running on the target
root@analog:~# iio_info iio_info version: 0.25 (git tag:8fb78e06) Libiio version: 0.25 (git tag: 8fb78e0) backends: local xml ip usb serial IIO context created with local backend. Backend version: 0.25 (git tag: 8fb78e0) Backend description string: Linux analog 6.1.54-v7l+ #3472 SMP Thu Jan 25 16:22:37 CET 2024 armv7l IIO context has 9 attributes: hw_carrier: Raspberry Pi 4 Model B Rev 1.4 dtoverlay: rpi-ltc2664,vc4-kms-v3d hw_model: 0x0001 on Raspberry Pi 4 Model B Rev 1.4 hw_mezzanine: 0x0001 hw_name: PMD-RPI-INTZ hw_vendor: Analog Devices, Inc. hw_serial: 13837e96-186d-45af-ac0b-e252c8d49a78 local,kernel: 6.1.54-v7l+ uri: local: IIO context has 2 devices: hwmon0: rpi_volt 1 channels found: in0: (input) 1 channel-specific attributes found: attr 0: lcrit_alarm value: 0 No trigger on this device iio:device0: ltc2664 4 channels found: voltage2: (output) 5 channel-specific attributes found: attr 0: offset value: -32768 attr 1: powerdown value: 0 attr 2: raw value: 1000 attr 3: raw_available value: [0 1 65535] attr 4: scale value: 0.305175781 voltage0: (output) 5 channel-specific attributes found: attr 0: offset value: -32768 attr 1: powerdown value: 1 attr 2: raw value: 58000 attr 3: raw_available value: [0 1 65535] attr 4: scale value: 0.305175781 voltage3: (output) 5 channel-specific attributes found: attr 0: offset value: -32768 attr 1: powerdown value: 0 attr 2: raw value: 42000 attr 3: raw_available value: [0 1 65535] attr 4: scale value: 0.305175781 voltage1: (output) 8 channel-specific attributes found: attr 0: offset value: -32768 attr 1: powerdown value: 0 attr 2: raw0 value: 22000 attr 3: raw1 value: 24000 attr 4: raw_available value: [0 1 65535] attr 5: scale value: 0.305175781 attr 6: symbol value: 0 attr 7: toggle_en value: 0 1 device-specific attributes found: attr 0: waiting_for_supplier value: 0 1 debug attributes found: debug attr 0: direct_reg_access ERROR: Operation not supported (95) No trigger on this device root@analog:~#
Show device name
This specifies any shell prompt running on the target
root@analog:/sys/bus/iio/devices/iio:device0> cat name ltc2664
Show scale
Description:
scale to be applied to out_voltage0_raw and out_voltage1_raw in order to obtain the measured voltage in millivolts.
This specifies any shell prompt running on the target
root@analog:/sys/bus/iio/devices/iio:device0> cat out_voltage_scale 0.305175781
Show offset
Description:
/sys/bus/iio/devices/iio:deviceX/out_offset_raw
Raw offset to be applied to out_voltage_raw in order to obtain the measured voltage in millivolts. The offset is applied before scale is applied.
This specifies any shell prompt running on the target
root@analog:/sys/bus/iio/devices/iio:device0> cat out_voltage_offset -32768
Set channel Y output voltage
Description:
/sys/bus/iio/devices/iio:deviceX/out_voltageY_raw
Raw (unscaled, no bias etc.) output voltage for channel Y.
This specifies any shell prompt running on the target
root@analog:/sys/bus/iio/devices/iio:device0> echo 10000 > out_voltage0_raw
U = (out_voltage0_raw + out_voltage0_offset) * out_voltage0_scale = (10000 - 32768) * 0.305175781mV = -6948.24 mV
Enable power down mode on output Y
/sys/bus/iio/devices/iio:deviceX/out_voltageY_powerdown
Description:
Writing 1 causes output Y to enter the power down mode. Clearing returns to normal operation.
This specifies any shell prompt running on the target
root@analog:/sys/bus/iio/devices/iio:device0> echo 1 > out_voltage0_powerdown root@analog:/sys/bus/iio/devices/iio:device0> cat out_voltage0_powerdown 1 root@analog:/sys/bus/iio/devices/iio:device0> echo 0 > out_voltage0_powerdown root@analog:/sys/bus/iio/devices/iio:device0> cat out_voltage0_powerdown 0
Test example
Using:
- DC2376A-A LTC2664-16 Demo Board
- PMD-RPI-INTZ Raspberry Pi to PMOD/QuikEval™/LTpowerPlay® Adaptor HAT
- Raspberry Pi 4
- iio_attr part of the Libiio package.
This specifies any shell prompt running on the target
root@analog:~# iio_attr -c IIO context has 2 devices: hwmon0, rpi_volt: found 1 channels iio:device0, ltc2664: found 4 channels root@analog:~# iio_attr -c ltc2664 dev 'ltc2664', channel 'voltage2' (output), found 5 channel-specific attributes dev 'ltc2664', channel 'voltage0' (output), found 5 channel-specific attributes dev 'ltc2664', channel 'voltage3' (output), found 5 channel-specific attributes dev 'ltc2664', channel 'voltage1' (output), found 8 channel-specific attributes root@analog:~# iio_attr -c ltc2664 voltage0 dev 'ltc2664', channel 'voltage0' (output), attr 'offset', value '-32768' dev 'ltc2664', channel 'voltage0' (output), attr 'powerdown', value '1' dev 'ltc2664', channel 'voltage0' (output), attr 'raw', value '1' dev 'ltc2664', channel 'voltage0' (output), attr 'raw_available', value '[0 1 65535]' dev 'ltc2664', channel 'voltage0' (output), attr 'scale', value '0.305175781' root@analog:~# iio_attr -c ltc2664 voltage0 raw 10000 10000 root@analog:~#
More Information
- IIO mailing list: linux [dash] iio [at] vger [dot] kernel [dot] org
resources/tools-software/linux-drivers/iio-dac/ltc2664.txt · Last modified: 26 Jan 2024 14:28 by Michael Hennerich