world leader in high performance signal processing
This version (09 Nov 2011 10:16) was approved by mhennerich.The Previously approved version (09 Nov 2011 10:15) is available.Diff

AD7291 IIO ADC Linux Driver

Supported Devices

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 Yes

Files

Function File
driver drivers/staging/iio/adc/ad7291.c

Example platform device initialization

Specifying reference voltage via the regulator framework

In case the AD7291 on-chip 2.5V reference is not used, this driver requires specifying the reference voltage, by using the Linux regulator framework.

Below example specifies a 3.3 Volt reference for the I2C device 0-002a on I2C-Bus 0. (0-002a)

#if defined(CONFIG_REGULATOR_FIXED_VOLTAGE) || defined(CONFIG_REGULATOR_FIXED_VOLTAGE_MODULE)
static struct regulator_consumer_supply ad7291_consumer_supplies[] = {
	REGULATOR_SUPPLY("vcc", "0-002a"),
};
 
static struct regulator_init_data board_avdd_reg_init_data = {
	.constraints	= {
		.name	= "3V3",
		.valid_ops_mask = REGULATOR_CHANGE_STATUS,
	},
	.consumer_supplies = ad7291_consumer_supplies,
	.num_consumer_supplies = ARRAY_SIZE(ad7291_consumer_supplies),
};
 
static struct fixed_voltage_config board_vdd_pdata = {
	.supply_name	= "board-3V3",
	.microvolts	= 3300000,
	.gpio		= -EINVAL,
	.enabled_at_boot = 0,
	.init_data	= &board_avdd_reg_init_data,
};
static struct platform_device brd_voltage_regulator = {
	.name		= "reg-fixed-voltage",
	.id		= -1,
	.num_resources	= 0,
	.dev		= {
		.platform_data	= &board_vdd_pdata,
	},
};
#endif
static struct platform_device *board_devices[] __initdata = {
#if defined(CONFIG_REGULATOR_FIXED_VOLTAGE) || defined(CONFIG_REGULATOR_FIXED_VOLTAGE_MODULE)
	&brd_voltage_regulator
#endif
};
static int __init board_init(void)
{
	[--snip--]
 
	platform_add_devices(board_devices, ARRAY_SIZE(board_devices));
 
	[--snip--]
 
	return 0;
}
arch_initcall(board_init);

Declaring I2C devices

Unlike PCI or USB devices, I2C devices are not enumerated at the hardware level. Instead, the software must know which devices are connected on each I2C bus segment, and what address these devices are using. For this reason, the kernel code must instantiate I2C devices explicitly. There are different ways to achieve this, depending on the context and requirements. However the most common method is to declare the I2C devices by bus number.

This method is appropriate when the I2C bus is a system bus, as in many embedded systems, wherein each I2C bus has a number which is known in advance. It is thus possible to pre-declare the I2C devices that inhabit this bus. This is done with an array of struct i2c_board_info, which is registered by calling i2c_register_board_info().

So, to enable such a driver one need only edit the board support file by adding an appropriate entry to i2c_board_info.

For more information see: Documentation/i2c/instantiating-devices

21 Oct 2010 16:10 · Michael Hennerich

Depending on the converter IC used, you may need to set the I2C_BOARD_INFO name accordingly, matching your part name.

static struct i2c_board_info __initdata board_i2c_board_info[] = {
#if defined(CONFIG_AD7291) || defined(CONFIG_AD7291_MODULE)
	{
		I2C_BOARD_INFO("ad7291", 0x2A),
		.irq = IRQ_PG14,
	},
#endif
};
static int __init board_init(void)
{
	[--snip--]
 
	i2c_register_board_info(0, board_i2c_board_info,
				ARRAY_SIZE(board_i2c_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 driver depends on CONFIG_I2C

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 AD7291 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

root:/sys/bus/iio/devices> cd iio:device0

root:/sys/devices/platform/i2c-bfin-twi.0/i2c-0/0-002a/iio:device0> ls -l
-r--r--r--    1 root     root          4096 Jan  1 00:38 dev
drwxr-xr-x    2 root     root             0 Jan  1 00:38 events
-rw-r--r--    1 root     root          4096 Jan  1 00:38 in_temp0_mean_raw
-r--r--r--    1 root     root          4096 Jan  1 00:38 in_temp0_raw
-rw-r--r--    1 root     root          4096 Jan  1 00:38 in_temp0_scale
-r--r--r--    1 root     root          4096 Jan  1 00:38 in_voltage0_raw
-r--r--r--    1 root     root          4096 Jan  1 00:38 in_voltage1_raw
-r--r--r--    1 root     root          4096 Jan  1 00:38 in_voltage2_raw
-r--r--r--    1 root     root          4096 Jan  1 00:38 in_voltage3_raw
-r--r--r--    1 root     root          4096 Jan  1 00:38 in_voltage4_raw
-r--r--r--    1 root     root          4096 Jan  1 00:38 in_voltage5_raw
-r--r--r--    1 root     root          4096 Jan  1 00:38 in_voltage6_raw
-r--r--r--    1 root     root          4096 Jan  1 00:38 in_voltage7_raw
-rw-r--r--    1 root     root          4096 Jan  1 00:38 in_voltage_scale
-r--r--r--    1 root     root          4096 Jan  1 00:38 name
drwxr-xr-x    2 root     root             0 Jan  1 00:38 power
--w-------    1 root     root          4096 Jan  1 00:38 reset
lrwxrwxrwx    1 root     root             0 Jan  1 00:38 subsystem -> ../../../../../../bus/iio
-rw-r--r--    1 root     root          4096 Jan  1 00:38 uevent

Show device name

This specifies any shell prompt running on the target

root:/sys/devices/platform/i2c-bfin-twi.0/i2c-0/0-002a/iio:device0> cat name
ad7291

Show scale

Description:
scale to be applied to in_voltageX_raw in order to obtain the measured voltage in millivolts.

This specifies any shell prompt running on the target

root:/sys/devices/platform/i2c-bfin-twi.0/i2c-0/0-002a/iio:device0> cat in_voltage_scale
0.610000

Show channel 0 measurement

Description:
Raw unscaled voltage measurement on channel 0

ADC Input Channel name
VIN0 in_voltage0_raw
VIN1 in_voltage1_raw
VIN2 in_voltage2_raw
VIN3 in_voltage3_raw
VIN4 in_voltage4_raw
VIN5 in_voltage5_raw
VIN6 in_voltage6_raw
VIN7 in_voltage7_raw

This specifies any shell prompt running on the target

root:/sys/devices/platform/i2c-bfin-twi.0/i2c-0/0-002a/iio:device0> cat in_voltage0_raw
1641

U = in_voltage0_raw * in_voltage_scale = 1641 * 0.610000 = 1001,01 mV

Show internal temperature

Description: /sys/bus/iio/devices/iio:deviceX/in_temp0_raw
Shows raw unscaled temperature.

Channel name Description
in_temp0_raw Current temperature
in_temp0_mean_raw Averaged temperature

This specifies any shell prompt running on the target

root:/sys/devices/platform/i2c-bfin-twi.0/i2c-0/0-002a/iio:device0> cat in_temp0_raw
107
root:/sys/devices/platform/i2c-bfin-twi.0/i2c-0/0-002a/iio:device0> cat in_temp0_scale
250

T = in_temp0_raw * in_temp0_scale = 107 * 250 = 26750 = 26.75 °C

Hardware Events

Event Management

The Industrial I/O subsystem provides support for passing hardware generated events up to userspace.

In IIO events are not used for passing normal readings from the sensing devices to userspace, but rather for out of band information. Normal data reaches userspace through a low overhead character device - typically via either software or hardware buffer. The stream format is pseudo fixed, so is described and controlled via sysfs rather than adding headers to the data describing what is in it.

Pretty much all IIO events correspond to thresholds on some value derived from one or more raw readings from the sensor. They are provided by the underlying hardware.

Examples include:

  • Straight crossing a voltage threshold
  • Moving average crosses a threshold
  • Motion detectors (lots of ways of doing this).
  • Thresholds on sum squared or rms values.
  • Rate of change thresholds.
  • Lots more variants…

Events have timestamps.

The Interface:

  • Single user at a time.
  • Simple chrdev per device (aggregation across devices doesn't really make sense for IIO as you tend to really care which sensor caused the event rather than just that it happened.)

The format is:

/**
 * struct iio_event_data - The actual event being pushed to userspace
 * @id:		event identifier
 * @timestamp:	best estimate of time of event occurrence (often from
 *		the interrupt handler)
 */
struct iio_event_data {
	u64	id;
	s64	timestamp;
};
02 Mar 2011 15:16 · Michael Hennerich

Typical event attributes

/sys/bus/iio/devices/iio:deviceX/events
Configuration of which hardware generated events are passed up to user-space.

  • Threshold Events:

<type>Z[_name]_thresh[_rising|falling]_en
Event generated when channel passes a threshold in the specified (_rising|_falling) direction. If the direction is not specified, then either the device will report an event which ever direction a single threshold value is called in (e.g. <type>[Z][_name]_<raw|input>_thresh_value) or <type>[Z][_name]_<raw|input>_thresh_rising_value and <type>[Z][_name]_<raw|input>_thresh_falling_value may take different values, but the device can only enable both thresholds or neither. Note the driver will assume the last p events requested are to be enabled where p is however many it supports (which may vary depending on the exact set requested. So if you want to be sure you have set what you think you have, check the contents of these attributes after everything is configured. Drivers may have to buffer any parameters so that they are consistent when a given event type is enabled a future point (and not those for whatever event was previously enabled).

<type>Z[_name]_thresh[_rising|falling]_value
Specifies the value of threshold that the device is comparing against for the events enabled by <type>Z[_name]_thresh[_rising|falling]_en. If separate attributes exist for the two directions, but direction is not specified for this attribute, then a single threshold value applies to both directions. The raw or input element of the name indicates whether the value is in raw device units or in processed units (as _raw and _input do on sysfs direct channel read attributes).

  • Rate of Change Events:

<type>[Z][_name]_roc[_rising|falling]_en
Event generated when channel passes a threshold on the rate of change (1st differential) in the specified (_rising|_falling) direction. If the direction is not specified, then either the device will report an event which ever direction a single threshold value is called in (e.g. <type>[Z][_name]_<raw|input>_roc_value) or <type>[Z][_name]_<raw|input>_roc_rising_value and <type>[Z][_name]_<raw|input>_roc_falling_value may take different values, but the device can only enable both rate of change thresholds or neither. Note the driver will assume the last p events requested are to be enabled where p is however many it supports (which may vary depending on the exact set requested. So if you want to be sure you have set what you think you have, check the contents of these attributes after everything is configured. Drivers may have to buffer any parameters so that they are consistent when a given event type is enabled a future point (and not those for whatever event was previously enabled).

<type>[Z][_name]_roc[_rising|falling]_value
Specifies the value of rate of change threshold that the device is comparing against for the events enabled by <type>[Z][_name]_roc[_rising|falling]_en. If separate attributes exist for the two directions, but direction is not specified for this attribute, then a single threshold value applies to both directions. The raw or input element of the name indicates whether the value is in raw device units or in processed units (as _raw and _input do on sysfs direct channel read attributes).

  • Magnitude Events:

<type>Z[_name]_mag[_rising|falling]_en
Similar to in_accel_x_thresh[_rising|_falling]_en, but here the magnitude of the channel is compared to the threshold, not its signed value.

<type>Z[_name]_mag[_rising|falling]_value
The value to which the magnitude of the channel is compared. If number or direction is not specified, applies to all channels of this type.

  • Temporal Conditions:

<type>[Z][_name][_thresh|_roc][_rising|falling]_period
Period of time (in seconds) for which the condition must be met before an event is generated. If direction is not specified then this period applies to both directions.

02 Mar 2011 15:16 · Michael Hennerich

Supported Events

Event Attributes
Channel Temp
in_temp0_thresh_both_hyst_raw
in_temp0_thresh_falling_en
in_temp0_thresh_falling_value
in_temp0_thresh_rising_en
in_temp0_thresh_rising_value
Channel VIN0
in_voltage0_thresh_both_hyst_raw
in_voltage0_thresh_falling_en
in_voltage0_thresh_falling_value
in_voltage0_thresh_rising_en
in_voltage0_thresh_rising_value
Channel VIN1
in_voltage1_thresh_both_hyst_raw
in_voltage1_thresh_falling_en
in_voltage1_thresh_falling_value
in_voltage1_thresh_rising_en
in_voltage1_thresh_rising_value
Channel VIN2
in_voltage2_thresh_both_hyst_raw
in_voltage2_thresh_falling_en
in_voltage2_thresh_falling_value
in_voltage2_thresh_rising_en
in_voltage2_thresh_rising_value
Channel VIN3
in_voltage3_thresh_both_hyst_raw
in_voltage3_thresh_falling_en
in_voltage3_thresh_falling_value
in_voltage3_thresh_rising_en
in_voltage3_thresh_rising_value
Channel VIN4
in_voltage4_thresh_both_hyst_raw
in_voltage4_thresh_falling_en
in_voltage4_thresh_falling_value
in_voltage4_thresh_rising_en
in_voltage4_thresh_rising_value
Channel VIN5
in_voltage5_thresh_both_hyst_raw
in_voltage5_thresh_falling_en
in_voltage5_thresh_falling_value
in_voltage5_thresh_rising_en
in_voltage5_thresh_rising_value
Channel VIN6
in_voltage6_thresh_both_hyst_raw
in_voltage6_thresh_falling_en
in_voltage6_thresh_falling_value
in_voltage6_thresh_rising_en
in_voltage6_thresh_rising_value
Channel VIN7
in_voltage7_thresh_both_hyst_raw
in_voltage7_thresh_falling_en
in_voltage7_thresh_falling_value
in_voltage7_thresh_rising_en
in_voltage7_thresh_rising_value

More Information