AD5421 IIO DAC Linux驱动程序

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This version (11 Feb 2016 20:52) was approved by Lars-Peter Clausen.The Previously approved version (20 Nov 2015 15:10) is available.

AD5421 IIO DAC Linux Driver
Source Code
- Status
- Files
Example platform device initialization
- Declaring SPI slave devices
Adding Linux driver support
Hardware configuration
Driver testing
More Information

AD5421 IIO DAC Linux Driver

Supported Devices

AD5421

Reference Circuits

Evaluation Boards

EVAL-AD5421SDZ

Description

This is a Linux industrial I/O (IIO) subsystem driver, targeting multi-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 IIO for more information.

Source Code

Status

Source	Mainlined
git	Yes

Files

Function	File
driver	drivers/iio/dac/ad5421.c

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

The ad5421 platform data is used to describe how the chip is configured on a specific board.

/**
 * enum ad5421_current_range - Current range the AD5421 is configured for.
 * @AD5421_CURRENT_RANGE_4mA_20mA: 4 mA to 20 mA (RANGE1,0 pins = 00)
 * @AD5421_CURRENT_RANGE_3mA8_21mA: 3.8 mA to 21 mA (RANGE1,0 pins = x1)
 * @AD5421_CURRENT_RANGE_3mA2_24mA: 3.2 mA to 24 mA (RANGE1,0 pins = 10)
 */
 
enum ad5421_current_range {
    AD5421_CURRENT_RANGE_4mA_20mA,
    AD5421_CURRENT_RANGE_3mA8_21mA,
    AD5421_CURRENT_RANGE_3mA2_24mA,
};
 
/**
 * struct ad5421_platform_data - AD5421 DAC driver platform data
 * @external_vref: whether an external reference voltage is used or not
 * @current_range: Current range the AD5421 is configured for
 */
 
struct ad5421_platform_data {
    bool external_vref;
    enum ad5421_current_range current_range;
};

If no platform data is given, the driver will assume an internal reference voltage and a current range of 4 mA to 20 mA.

struct ad5421_platform_data ad5421_pdata {
	.external_vref = true,
	.current_range = AD5421_CURRENT_RANGE_3mA2_24mA,
};
 
static int __init board_init(void)
{
	[--snip--]
 
	platform_add_devices(board_devices, ARRAY_SIZE(board_devices));
 
	[--snip--]
 
	return 0;
}
arch_initcall(board_init);

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

static struct spi_board_info board_spi_board_info[] __initdata = {
#if defined(CONFIG_AD5421_SPI) || /
 	defined(CONFIG_AD5421_SPI_MODULE)
	{
		/* the modalias must be the same as spi device driver name */
		.modalias = "ad5421", /* Name of spi_driver for this device */
		.max_speed_hz = 30000000,     /* max spi clock (SCK) speed in HZ */
		.bus_num = 0, /* Framework bus number */
		.chip_select = 3, /* Framework chip select */
		.mode = SPI_MODE_2,
		.irq = IRQ_PF4,
		.platform_data = &ad5421_pdata,
	},
#endif
};

Adding Linux driver support

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

The ad5421 Driver depends on CONFIG_SPI

Linux Kernel Configuration
    Device Drivers  --->
        ...
        <*>     Industrial I/O support --->
            --- Industrial I/O support
            ...
            Digital to analog converters  ---> 
                ...
                <*>  Analog Devices AD5421 DAC driver
                ...
            ...
        ...

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