LTC2664

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

LTC2664

Evaluation Boards

DC2376A-A

Description

This is a Linux industrial I/O (Linux Industrial I/O Subsystem) 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 Linux Industrial I/O Subsystem for more information.

Source Code

Status

Source	Mainlined?
git	WIP

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 device
spi-max-frequency: Maximum SPI clock frequency
Vdd-supply: VDD voltage supply regulator
iovcc-supply: Digital Input/Output Supply Voltage.
adi,manual-span-operation-config:
Channel nodes with reg, adi,manual-span-operation-config and optionally adi,toggle-mode properties.

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.

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#

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

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.

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.

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.

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.

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.

https://wiki.analog.com/_media/resources/tools-software/linux-drivers/iio-dac/ltc2664.jpg

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:~#