AD5764 IIO四通道Linux驱动程序DAC

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This version (05 Jan 2021 17:01) was approved by Ioana Chelaru.The Previously approved version (11 Feb 2016 20:55) is available.

AD5764 IIO Quad-Channel DAC Linux Driver
Source Code
- Status
- Files
Example platform device initialization
- Specifying reference voltage via the regulator framework
  - Declaring SPI slave devices
Adding Linux driver support
Hardware configuration
Driver testing
More Information

AD5764 IIO Quad-Channel DAC Linux Driver

Supported Devices

Evaluation Boards

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/ad5764.c

Example platform device initialization

Specifying reference voltage via the regulator framework

Depending on the part it will either have an internal reference(AD5764R, AD5744R) or use an external reference(AD5764, AD5744) In case an external reference voltage is used the regulator framework must be used to provide the regulator supplys. The supplys must be be called “vrefAB” and “vrefCD”.

Below example specifies a 2.5 Volt reference for the SPI device 3 on SPI-Bus 0. (spi0.3)

#if IS_ENABLED(CONFIG_REGULATOR_FIXED_VOLTAGE)
static struct regulator_consumer_supply ad5764_consumer_supplies[] = {
	REGULATOR_SUPPLY("vrefAB", "spi0.3"),
	REGULATOR_SUPPLY("vrefCD", "spi0.3"),
};
 
static struct regulator_init_data stamp_avdd_reg_init_data = {
	.constraints	= {
		.name	= "2V5",
		.valid_ops_mask = REGULATOR_CHANGE_STATUS,
	},
	.consumer_supplies = ad5764_consumer_supplies,
	.num_consumer_supplies = ARRAY_SIZE(ad5764_consumer_supplies),
};
 
static struct fixed_voltage_config stamp_vdd_pdata = {
	.supply_name	= "board-2V5",
	.microvolts	= 2500000,
	.gpio		= -EINVAL,
	.enabled_at_boot = 0,
	.init_data	= &stamp_avdd_reg_init_data,
};
static struct platform_device brd_voltage_regulator = {
	.name		= "reg-fixed-voltage",
	.id		= -1,
	.num_resources	= 0,
	.dev		= {
		.platform_data	= &stamp_vdd_pdata,
	},
};
#endif

static struct platform_device *board_devices[] __initdata = {
#if IS_ENABLED(CONFIG_REGULATOR_FIXED_VOLTAGE)
	&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 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

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 IS_ENABLED(CONFIG_AD5764)
	{
		/* the modalias must be the same as spi device driver name */
		.modalias = "ad5764", /* Name of spi_driver for this device */
		.max_speed_hz = 1000000,     /* max spi clock (SCK) speed in HZ */
		.bus_num = 0, /* Framework bus number */
		.chip_select = 3, /* Framework chip select */
		.mode = SPI_MODE_1,
	},
#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 AD5764 Driver depends on CONFIG_SPI_MASTER

Linux Kernel Configuration
    Device Drivers  --->
        ...
        <*>     Industrial I/O support --->
            --- Industrial I/O support
            ...
            Digital to analog converters  ---> 
                ...
                <*>  Analog Devices AD5764/64R/44/44R DAC drive
                ...
            ...
        ...

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