AD5449
AD5449 IIO DAC Linux Driver.
Supported Devices
Evaluation Boards
Reference Circuits
Description
This is a Linux industrial I/O (Linux Industrial I/O Subsystem) subsystem driver, targeting single- and dual-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 Linux Industrial I/O Subsystem for more information.
Source Code
Status
Files
Function |
File |
|---|---|
driver |
|
include |
Adding Linux driver support
Kernel configuration
Configure kernel with make menuconfig (alternatively use make xconfig or
make qconfig)
Note
The AD5449 Driver depends on CONFIG_SPI
Linux Kernel Configuration
Device Drivers --->
...
<*> Industrial I/O support --->
--- Industrial I/O support
...
Digital to analog converters --->
...
<*> Analog Devices AD5449 and similar DACs drive
...
...
...
Platform-data configuration
Example platform device initialization
Specifying reference voltage via the regulator framework
Below example specifies a 2.5 Volt reference for the SPI device 3 on SPI-Bus 0. (spi0.3)
#if defined(CONFIG_REGULATOR_FIXED_VOLTAGE) || defined(CONFIG_REGULATOR_FIXED_VOLTAGE_MODULE)
static struct regulator_consumer_supply ad5449_consumer_supplies[] = {
REGULATOR_SUPPLY("VREFA", "spi0.3"),
REGULATOR_SUPPLY("VREFB", "spi0.3"),
/* Single-channel models instead request "VREF". */
};
static struct regulator_init_data stamp_avdd_reg_init_data = {
.constraints = {
.name = "2V5",
.valid_ops_mask = REGULATOR_CHANGE_STATUS,
},
.consumer_supplies = ad5449_consumer_supplies,
.num_consumer_supplies = ARRAY_SIZE(ad5449_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 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);
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: Overview of Linux kernel SPI support
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 = {
{
/* the modalias must be the same as spi device driver name */
.modalias = "ad5449", /* 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_2,
},
};
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);
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.
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 1 02:20 dev
-r--r--r-- 1 root root 4096 Jan 1 02:20 name
-rw-r--r-- 1 root root 4096 Jan 1 02:25 out_voltage0_raw
-rw-r--r-- 1 root root 4096 Jan 1 02:20 out_voltage0_scale
-rw-r--r-- 1 root root 4096 Jan 1 02:25 out_voltage1_raw
-rw-r--r-- 1 root root 4096 Jan 1 02:20 out_voltage1_scale
drwxr-xr-x 2 root root 0 Jan 1 02:20 power
lrwxrwxrwx 1 root root 0 Jan 1 02:20 subsystem -> ../../../../../../../bus/iio
-rw-r--r-- 1 root root 4096 Jan 1 02:20 uevent
Note
For DACs with only one output channel there will be no out_voltage1_raw and out_voltage1_scale files
Identify the device
root:/sys/devices/platform/bfin-spi.0/spi0.3/iio:device0> cat name
ad5449
Basic operation
Show scale
Description: scale for converting the programmed DAC code to its reference-based nominal value. For the current-output multiplying DACs in this family, the actual output voltage and polarity also depend on the external current-to-voltage amplifier and feedback configuration. Verify the board transfer function before interpreting raw × scale as a measured output voltage.
root:/sys/devices/platform/bfin-spi.0/spi0.3/iio:device0> cat out_voltage0_scale
0.610351562
For AD5449 with a 2.5 V reference, 1234 codes correspond to about 753.174 mV.
Use out_voltage0_scale in the following equation.
Set channel 0
Description: /sys/bus/iio/devices/iio:deviceX/out_voltageY_raw
Raw (unscaled, no bias etc.) output voltage for channel Y.
root:/sys/devices/platform/bfin-spi.0/spi0.3/iio:device0> echo 1234 > out_voltage0_raw
U = out_voltage0_raw * out_voltage_scale = 1234 * 0.152mV = 187.568 mV