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This version (06 Feb 2014 11:23) was approved by larsc.The Previously approved version (18 Feb 2013 15:02) is available.Diff

AD5380 IIO Multi-Channel DAC Linux Driver

Supported Devices

Reference Circuits

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 git

Files

Function File
driver drivers/iio/dac/ad5380.c

Example platform device initialization

Specifying reference voltage via the regulator framework

The AD538X/AD539X can either use an internal or an external reference voltage. To use an external reference voltage use the regulator framework to provide a regulator supply. The supply should be called “vref”.

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 ad5380_consumer_supplies[] = {
	REGULATOR_SUPPLY("vref", "spi0.3"),
};
 
static struct regulator_init_data stamp_avdd_reg_init_data = {
	.constraints	= {
		.name	= "2V5",
		.valid_ops_mask = REGULATOR_CHANGE_STATUS,
	},
	.consumer_supplies = ad5380_consumer_supplies,
	.num_consumer_supplies = ARRAY_SIZE(ad5380_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 · 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 IS_ENABLED(CONFIG_AD5380)
	{
		/* the modalias must be the same as spi device driver name */
		.modalias = "ad5380-5", /* 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);

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 modalias accordingly, matching your part name.

The part name needs a -3 or -5 depending on whether a 1.25V or 2.5V internal reference is used. E.g. “ad5380-5” or “ad5391-3”.

The I2C device id depends on the AD0 and AD1 pin settings and needs to be set according to your board setup.

AD1 AD0 I2C device id
0 0 0x54
0 1 0x55
1 0 0x56
1 1 0x57

In this example we assume ADDR0=0 and ADDR1=0.

static struct i2c_board_info __initdata bfin_i2c_board_info[] = {
 
	[--snip--]
	{
		I2C_BOARD_INFO("a5380", 0x38),
	},
	[--snip--]
}
static int __init stamp_init(void)
{
	[--snip--]
	i2c_register_board_info(0, bfin_i2c_board_info,
				ARRAY_SIZE(bfin_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 AD5380 Driver depends on CONFIG_SPI_MASTER or CONFIG_I2C

Linux Kernel Configuration
    Device Drivers  --->
        ...
        <*>     Industrial I/O support --->
            --- Industrial I/O support
            ...
            Digital to analog converters  ---> 
                ...
                <*>  Analog Devices AD5380/81/82/83/84/90/91/92 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 · 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/bfin-spi.0/spi0.3/iio:device0> ls -l
-r--r--r--    1 root     root          4096 Jan  2 21:54 dev
-r--r--r--    1 root     root          4096 Jan  2 21:54 name
-rw-r--r--    1 root     root          4096 Jan  2 21:54 out_voltage0_calibbias
-rw-r--r--    1 root     root          4096 Jan  2 21:54 out_voltage0_calibscale
-rw-r--r--    1 root     root          4096 Jan  2 21:54 out_voltage0_raw
-rw-r--r--    1 root     root          4096 Jan  2 21:54 out_voltage10_calibbias
-rw-r--r--    1 root     root          4096 Jan  2 21:54 out_voltage10_calibscale
-rw-r--r--    1 root     root          4096 Jan  2 21:54 out_voltage10_raw
...
-rw-r--r--    1 root     root          4096 Jan  3 21:54 out_voltage9_calibbias
-rw-r--r--    1 root     root          4096 Jan  3 21:54 out_voltage9_calibscale
-rw-r--r--    1 root     root          4096 Jan  3 21:54 out_voltage9_raw
-rw-r--r--    1 root     root          4096 Jan  2 21:54 out_voltage_powerdown
-rw-r--r--    1 root     root          4096 Jan  3 21:54 out_voltage_powerdown_mode
-r--r--r--    1 root     root          4096 Jan  3 21:54 out_voltage_powerdown_mode_available
-rw-r--r--    1 root     root          4096 Jan  3 21:54 out_voltage_scale
drwxr-xr-x    2 root     root             0 Jan  2 21:54 power
lrwxrwxrwx    1 root     root             0 Jan  2 21:54 subsystem -> ../../../../../bus/iio
-rw-r--r--    1 root     root          4096 Jan  2 21:54 uevent

Show device name

This specifies any shell prompt running on the target

root:/sys/devices/platform/bfin-spi.0/spi0.3/iio:device0> cat name
ad5380

Show scale

Description:
/sys/bus/iio/devices/iio:deviceX/out_scale_raw

scale to be applied to out_voltageY_raw in order to obtain the measured voltage in millivolts.

This specifies any shell prompt running on the target

root:/sys/devices/platform/bfin-spi.0/spi0.3/iio:device0> cat out_voltage_scale
0.305000

Set channel Y output voltage

Description:
/sys/bus/iio/devices/iio:deviceX/out_voltageY_raw

Raw (unscaled, no bias etc.) output voltage for channel Y.

This specifies any shell prompt running on the target

root:/sys/devices/platform/bfin-spi.0/spi0.3/iio:device0> echo 10000 > out_voltage0_raw

U = out_voltage0_raw * out_voltage0_scale = 10000 * 0,305000 mV = 305,00 mV

Calibrate channel Y gain

Description:
/sys/bus/iio/devices/iio:deviceX/out_voltageY_calibscale

Each channel has an adjustable gain which can be used to calibrate the channel's scale and compensate for full-scale errors. The default value is 16382. The minimum value is 0, the maximum value is 16383.

If scale calibration is used the following formula can be used calculate the output voltage:
U = ( ( out_voltageY_raw * ( out_voltageY_calibscale + 2) ) / 2^14 + out_voltageY_calibbias ) * out_voltageY_scale

Calibrate channel Y offset

Description:
/sys/bus/iio/devices/iio:deviceX/out_voltageY_calibbias

Each channel has an adjustable offset which can be used to calibrate the channel's offset and compensate for zero-scale errors. The default value is 0. The minimum value is -8192, the maximum value is 8191.

If offset calibration is used the following formula can be used calculate the output voltage:
U = ( ( out_voltageY_raw * ( out_voltageY_calibscale + 2 ) ) / 2^14 + out_voltageY_calibbias ) * out_voltageY_scale

Enable power down mode for the device

/sys/bus/iio/devices/iio:deviceX/out_voltage_powerdown

Description:
Writing 1 causes the device to enter power down mode. Clearing returns to normal operation.

This specifies any shell prompt running on the target

root:/sys/devices/platform/bfin-spi.0/spi0.3/iio:device0> echo 1 > out_voltage_powerdown
root:/sys/devices/platform/bfin-spi.0/spi0.3/iio:device0> cat out_voltage_powerdown
1
root:/sys/devices/platform/bfin-spi.0/spi0.3/iio:device0> echo 0 > out_voltage_powerdown
root:/sys/devices/platform/bfin-spi.0/spi0.3/iio:device0> cat out_voltage_powerdown
0

List available power down modes

/sys/bus/iio/devices/iio:deviceX/out_voltage_powerdown_mode_available

Description:
Lists all available output power down modes.

This specifies any shell prompt running on the target

root:/sys/devices/platform/bfin-spi.0/spi0.3/iio:device0> cat out_voltage_powerdown_mode_available
100kohm_to_gnd three_state

Set power down mode

/sys/bus/iio/devices/iio:deviceX/out_voltage_powerdown_mode

Description:
Specifies the output power down mode. DAC output stage is disconnected from the amplifier and

100kohm_to_gnd connected to ground via an 100kOhm resistor
three_state left floating

For a list of available output power down options read out_voltage_powerdown_mode_available.

This specifies any shell prompt running on the target

root:/sys/devices/platform/bfin-spi.0/spi0.3/iio:device0> echo three_state > out_voltage_powerdown_mode
root:/sys/devices/platform/bfin-spi.0/spi0.3/iio:device0> cat out_voltage_powerdown_mode
three_state

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