AD7291 IIO ADC Linux驱动程序

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This version (20 Dec 2016 10:24) was approved by Lars-Peter Clausen.The Previously approved version (11 Feb 2016 20:45) is available.

AD7291 IIO ADC Linux Driver
Source Code
- Status
- Files
Example platform device initialization
- Specifying reference voltage via the regulator framework
  - Declaring I2C devices
Adding Linux driver support
Hardware configuration
Driver testing
Hardware Events
More Information

AD7291 IIO ADC Linux Driver

Supported Devices

AD7291

Evaluation Boards

EVAL-AD7291SDZ

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/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

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