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This version (21 Nov 2012 18:55) was approved by larsc.The Previously approved version (11 Oct 2012 18:59) is available.Diff

AD7192 IIO High Precision ADC Linux Driver

Supported Devices

Reference Circuits

Evaluation Boards

Description

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

Source Code

Status

Source Mainlined?
git git

Files

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.

21 Oct 2010 16:10 · Michael Hennerich

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,
};

Declaring SPI slave devices

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: Documentation/spi/spi-summary

21 Oct 2010 16:10 · Michael Hennerich

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);

Adding Linux driver support

Configure kernel with “make menuconfig” (alternatively use “make xconfig” or “make qconfig”)

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.

02 Mar 2011 15:16 · Michael Hennerich

This specifies any shell prompt running on the target

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

This specifies any shell prompt running on the target

root:/sys/devices/platform/bfin-spi.0/spi0.18/iio:device0> cat name
ad7192

Set sampling frequency / update rate

This specifies any shell prompt running on the target

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.

This specifies any shell prompt running on the target

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.

This specifies any shell prompt running on the target

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.

This specifies any shell prompt running on the target

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

This specifies any shell prompt running on the target

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

This specifies any shell prompt running on the target

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.

This specifies any shell prompt running on the target

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.

This specifies any shell prompt running on the target

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.

This specifies any shell prompt running on the target

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

This driver only supports it's own default trigger source ad7192-dev0

This specifies any shell prompt running on the target

root:/sys/devices/platform/bfin-spi.0/spi0.18/iio:device0> cat trigger/current_trigger
ad7192-dev0

Buffer management

This specifies any shell prompt running on the target

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.

scan_elements
The scan_elements directory contains interfaces for elements that will be captured for a single triggered sample set in the buffer.

02 Mar 2011 15:16 · Michael Hennerich

This specifies any shell prompt running on the target

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.

02 Mar 2011 15:16 · Michael Hennerich

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