AD7192
AD7192 IIO High Precision ADC Linux Driver.
Supported Devices
Reference Circuits
Evaluation Boards
Description
This is a Linux industrial I/O (Linux Industrial I/O Subsystem) subsystem driver, targeting multi 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 Linux Industrial I/O Subsystem for more information.
Source Code
Status
Files
Function |
File |
|---|---|
driver |
|
include |
Example platform device initialization
For compile time configuration, it’s common Linux practice to keep board- and application-specific configuration out of the main driver file, instead putting it into the board support file.
For devices on custom boards, as typical of embedded and SoC-(system-on-chip)
based hardware, Linux uses platform_data to point to board-specific structures
describing devices and how they are connected to the SoC. This can include
available ports, chip variants, preferred modes, default initialization,
additional pin roles, and so on. This shrinks the board-support packages (BSPs)
and minimizes board and application specific #ifdefs in drivers.
The reference voltage may vary between boards and models. The platform_data for
the device’s struct device holds this information.
/**
* struct ad7192_platform_data - platform/board specific information
* @vref_mv: the external reference voltage in millivolt
* @ext_clk_Hz: the external clock frequency in Hz, if not set
* the driver uses the internal clock (16.776 MHz)
* @clock_source_sel: [0..3]
* 0 External 4.92 MHz clock connected from MCLK1 to MCLK2
* 1 External Clock applied to MCLK2
* 2 Internal 4.92 MHz Clock not available at the MCLK2 pin
* 3 Internal 4.92 MHz Clock available at the MCLK2 pin
* @refin2_en: REFIN1/REFIN2 Reference Select (AD7190/2 only)
* @rej60_en: 50/60Hz notch filter enable
* @sinc3_en: SINC3 filter enable (default SINC4)
* @chop_en: CHOP mode enable
* @buf_en: buffered input mode enable
* @unipolar_en: unipolar mode enable
* @burnout_curr_en: constant current generators on AIN(+|-) enable
*/
struct ad7192_platform_data {
u16 vref_mv;
u32 ext_clk_Hz;
u8 clock_source_sel;
bool refin2_en;
bool rej60_en;
bool sinc3_en;
bool chop_en;
bool buf_en;
bool unipolar_en;
bool burnout_curr_en;
};
static struct ad7192_platform_data ad7192_pdata = {
.vref_mv = 3300,
.clock_source_sel = 2,
.refin2_en = true,
.rej60_en = false,
.sinc3_en = false,
.chop_en = false,
.buf_en = false,
.unipolar_en = true,
.burnout_curr_en = false,
};
Unlike PCI or USB devices, SPI devices are not enumerated at the hardware level. Instead, the software must know which devices are connected on each SPI bus segment, and what slave selects these devices are using. For this reason, the kernel code must instantiate SPI devices explicitly. The most common method is to declare the SPI devices by bus number.
This method is appropriate when the SPI bus is a system bus, as in many
embedded systems, wherein each SPI bus has a number which is known in advance.
It is thus possible to pre-declare the SPI devices that inhabit this bus. This
is done with an array of struct spi_board_info, which is registered by
calling spi_register_board_info().
For more information see: Overview of Linux kernel SPI support
Depending on the converter IC used, you may need to set the modalias accordingly, matching your part name. It may also required to adjust max_speed_hz. Please consult the datasheet, for maximum spi clock supported by the device in question.
static struct spi_board_info board_spi_board_info[] __initdata = {
#if defined(CONFIG_AD7192) \
|| defined(CONFIG_AD7192_MODULE)
{
.modalias = "ad7192",
.max_speed_hz = 1000000, /* max spi clock (SCK) speed in HZ */
.bus_num = 0,
.chip_select = GPIO_PF10 + MAX_CTRL_CS, /* CS, change it for your board */
.platform_data = &ad7192_pdata,
.mode = SPI_MODE_3,
.irq = IRQ_PF6,
},
#endif
};
static int __init board_init(void)
{
[--snip--]
spi_register_board_info(board_spi_board_info, ARRAY_SIZE(board_spi_board_info));
[--snip--]
return 0;
}
arch_initcall(board_init);
Device tree support
Device tree is the new method for describing non-discoverable hardware in Linux. This replaces former structure based method. For configuring a device using this drivers please follow the example bellow:
/dts-v1/;
/plugin/;
/ {
fragment@0 {
target-path = "/";
dvdd: fixedregulator@0 {
compatible = "regulator-fixed";
regulator-name = "fixed-supply";
regulator-min-microvolt = <3300000>;
regulator-max-microvolt = <3300000>;
regulator-boot-on;
};
};
fragment@1 {
target-path = "/";
avdd: fixedregulator@1 {
compatible = "regulator-fixed";
regulator-name = "fixed-supply2";
regulator-min-microvolt = <3300000>;
regulator-max-microvolt = <3300000>;
regulator-boot-on;
};
};
fragment@3 {
target = <&spi0>;
#address-cells = <1>;
#size-cells = <0>;
status = "okay";
ad7190@0 {
compatible = "adi,ad7190";
reg = <0>;
spi-max-frequency = <1000000>;
spi-cpol;
spi-cpha;
#interrupt-cells = <2>;
interrupts = <25 0x2>;
interrupt-parent = <&gpio>;
dvdd-supply = <&dvdd>;
avdd-supply = <&avdd>;
adi,reference-voltage-mv = /bits/ 16 <3300>;
adi,clock-source-select = [02];
adi,refin2-pins-enable;
adi,rejection-60-Hz-enable;
adi,chop-enable;
adi,buffer-enable;
adi,burnout-currents-enable;
adi,sinc3-filter-enable;
adi,unipolar-enable;
};
};
};
Important
Interrupt pin connection - interrupts = <25 0x2>; this line means that gpio pin 25 is used for the interrupt and it must be connect to the DOUT/RDY pin of AD7192 along with the SPI MISO.
Adding Linux driver support
Configure kernel with make menuconfig (alternatively use make xconfig or
make qconfig)
Note
The AD7192 Driver depends on CONFIG_SPI
Linux Kernel Configuration
Device Drivers --->
[*] Staging 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 AD7190 AD7192 AD7195 ADC driver
[--snip--]
Hardware configuration
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:/> cd /sys/bus/iio/devices/
root:/sys/bus/iio/devices> ls
iio:device0 trigger0
root:/sys/bus/iio/devices> cd iio:device0
root:/sys/devices/platform/bfin-spi.0/spi0.18/iio:device0> ls -l
-rw-r--r-- 1 root root 4096 Jan 4 16:59 bridge_switch_en
drwxr-xr-x 4 root root 0 Jan 4 16:59 buffer
-rw-r--r-- 1 root root 4096 Jan 4 16:59 in_voltage-in_voltage_scale
-r--r--r-- 1 root root 4096 Jan 4 16:59 in_voltage-in_voltage_scale_available
-r--r--r-- 1 root root 4096 Jan 4 16:59 in_voltage1-in_voltage2_raw
-r--r--r-- 1 root root 4096 Jan 4 16:59 in_voltage1_raw
-r--r--r-- 1 root root 4096 Jan 4 16:59 in_voltage2-in_voltage2_shorted_raw
-r--r--r-- 1 root root 4096 Jan 4 16:59 in_voltage2_raw
-r--r--r-- 1 root root 4096 Jan 4 16:59 in_voltage3-in_voltage4_raw
-r--r--r-- 1 root root 4096 Jan 4 16:59 in_voltage3_raw
-r--r--r-- 1 root root 4096 Jan 4 16:59 in_voltage4_raw
-rw-r--r-- 1 root root 4096 Jan 4 16:59 in_voltage_scale
-r--r--r-- 1 root root 4096 Jan 4 16:59 in_voltage_scale_available
-r--r--r-- 1 root root 4096 Jan 4 16:59 name
drwxr-xr-x 2 root root 0 Jan 4 16:59 power
-rw-r--r-- 1 root root 4096 Jan 5 11:38 sampling_frequency
lrwxrwxrwx 1 root root 0 Jan 4 16:59 subsystem -> ../../../../../bus/iio
-r--r--r-- 1 root root 4096 Jan 4 16:59 in_temp0_raw
-rw-r--r-- 1 root root 4096 Jan 4 16:59 in_temp0_scale
drwxr-xr-x 2 root root 0 Jan 4 16:59 trigger
-rw-r--r-- 1 root root 4096 Jan 4 16:59 uevent
root:/sys/devices/platform/bfin-spi.0/spi0.18/iio:device0>
Show device name
root:/sys/devices/platform/bfin-spi.0/spi0.18/iio:device0> cat name
ad7192
Set sampling frequency / update rate
root:/sys/devices/platform/bfin-spi.0/spi0.18/iio:device0> cat sampling_frequency
10
root:/sys/devices/platform/bfin-spi.0/spi0.18/iio:device0> echo 50 > sampling_frequency
root:/sys/devices/platform/bfin-spi.0/spi0.18/iio:device0> cat sampling_frequency
50
root:/sys/devices/platform/bfin-spi.0/spi0.18/iio:device0>
Show available scales for differential input channels
Lists all available scales for the differential input pairs:
ADC Input Pair |
Channel name |
|---|---|
AIN1(+) - AIN2(-) |
in_voltage1-in_voltage2_raw |
AIN3(+) - AIN4(-) |
in_voltage3-in_voltage4_raw |
AIN2(-) - AIN2(-) |
in_voltage2-in_voltage2_shorted_raw |
Setting these directly influences the ADC input range, by altering the GAIN amplifier.
root:/sys/devices/platform/bfin-spi.0/spi0.18/iio:device0> cat in_voltage-in_voltage_scale_available
0.000393390 0.000196690 0.000098340 0.000049170 0.000024580 0.000012290 0.000006140 0.000003070
Show available scales for pseudo-differential input channels
Lists all available scales for the differential input pairs:
ADC Input Pair |
Channel name |
|---|---|
AIN1 - AINCOM |
in_voltage1_raw |
AIN2 - AINCOM |
in_voltage2_raw |
AIN3 - AINCOM |
in_voltage3_raw |
AIN4 - AINCOM |
in_voltage4_raw |
Setting these directly influences the ADC input range, by altering the GAIN amplifier.
root:/sys/devices/platform/bfin-spi.0/spi0.18/iio:device0> cat in_voltage_scale_available
0.000393390 0.000196690 0.000098340 0.000049170 0.000024580 0.000012290 0.000006140 0.000003070
Set scale for differential input channels
Scale to be applied to in1-in2_raw, in2-in3_raw in order to obtain the measured voltage in millivolts. Allows the user to select one scale out of the available scales. If the written scale differs from the current scale. The driver performs full and zero offset calibration on all differential input channels.
root:/sys/devices/platform/bfin-spi.0/spi0.18/iio:device0> cat in_voltage-in_voltage_scale
0.000393390
root:/sys/devices/platform/bfin-spi.0/spi0.18/iio:device0> echo 0.000196690 > in_voltage-in_voltage_scale
root:/sys/devices/platform/bfin-spi.0/spi0.18/iio:device0> cat in_voltage-in_voltage_scale
0.000196690
Show channel in_voltage1 measurement
Description: Raw unscaled voltage measurement on channel in_voltage1
ADC Input Pair |
Channel name |
|---|---|
AIN1(+) - AIN2(-) |
in_voltage1-in_voltage2_raw |
AIN3(+) - AIN4(-) |
in_voltage3-in_voltage4_raw |
AIN2(-) - AIN2(-) |
in_voltage2-in_voltage2_shorted_raw |
AIN1 - AINCOM |
in_voltage1_raw |
AIN2 - AINCOM |
in_voltage2_raw |
AIN3 - AINCOM |
in_voltage3_raw |
AIN4 - AINCOM |
in_voltage4_raw |
root:/sys/devices/platform/bfin-spi.0/spi0.18/iio:device0> cat in1_raw
-1
U = in_voltage1_raw * in_voltage_scale = 3983772* 0.000393390 = 1567.17606708 mV
Show channel in_voltage1-in_voltage2 measurement
Description: Raw unscaled voltage measurement on channel in_voltage1-in_voltage2
root:/sys/devices/platform/bfin-spi.0/spi0.18/iio:device0> cat in_voltage1-in_voltage2_raw
-1
U = in_voltage1-in_voltage3_raw * in_voltage-in_voltage_scale = -1 * 0.000393390 = -0.000393390 mV
Show internal temperature
Description: /sys/bus/iio/devices/iio:deviceX/in_temp0_raw Shows raw unscaled temperature.
root:/sys/devices/platform/bfin-spi.0/spi0.18/iio:device0> cat in_temp0_raw
-175
Bride power-down switch control
Description: /sys/bus/iio/devices/iio:deviceX/bridge_switch_en Writing 1 closes the bridge switch.
root:/sys/devices/platform/bfin-spi.0/spi0.18/iio:device0> echo 1 > bridge_switch_en
root:/sys/devices/platform/bfin-spi.0/spi0.18/iio:device0> cat bridge_switch_en
1
root:/sys/devices/platform/bfin-spi.0/spi0.18/iio:device0> echo 0 > bridge_switch_en
AC excitation control (AD7195 only)
Description: /sys/bus/iio/devices/iio:deviceX/ac_excitation_en Writing 1 enables AC excitation on the AD7195 ACX strobes.
root:/sys/devices/platform/bfin-spi.0/spi0.18/iio:device0> echo 1 > ac_excitation_en
root:/sys/devices/platform/bfin-spi.0/spi0.18/iio:device0> cat ac_excitation_en
1
root:/sys/devices/platform/bfin-spi.0/spi0.18/iio:device0> echo 0 > ac_excitation_en
Trigger management
Note
This driver only supports it’s own default trigger source ad7192-dev0
root:/sys/devices/platform/bfin-spi.0/spi0.18/iio:device0> cat trigger/current_trigger
ad7192-dev0
Buffer management
root:/sys/devices/platform/bfin-spi.0/spi0.18/device0/iio:buffer> ls
enable length
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_bytesproperty.- 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/devices/platform/bfin-spi.0/spi0.18/iio:device0/scan_elements> ls
in_voltage1-in_voltage2_en in_voltage2_en in_voltage4_en
in_voltage1-in_voltage2_index in_voltage2_index in_voltage4_index
in_voltage1-in_voltage2_type in_voltage2_type in_voltage4_type
in_voltage1_en in_voltage3-in_voltage4_en in_temp0_en
in_voltage1_index in_voltage3-in_voltage4_index in_temp0_index
in_voltage1_type in_voltage3-in_voltage4_type in_temp0_type
in_voltage2-in_voltage2_shorted_en in_voltage3_en timestamp_en
in_voltage2-in_voltage2_shorted_index in_voltage3_index timestamp_index
in_voltage2-in_voltage2_shorted_type in_voltage3_type timestamp_type
root:/sys/devices/platform/bfin-spi.0/spi0.18/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.