AD5624
AD5624 IIO Quad-Channel DAC Linux Driver.
Supported Devices
Evaluation Boards
Description
This is a Linux industrial I/O (Linux Industrial I/O Subsystem) 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 Linux Industrial I/O Subsystem for more information.
Source Code
Status
Files
Function |
File |
|---|---|
driver |
|
include |
Example platform device initialization
Specifying reference voltage via the regulator framework
Tip
For chip variants with build in references such as the: ad5620-2500 ad5620-1250 ad5640-2500 ad5640-1250 ad5660-2500 ad5660-1250 specifying the reference voltage via the regulator framework is not mandatory.
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 ad5624_consumer_supplies[] = {
REGULATOR_SUPPLY("vcc", "spi0.3"),
};
static struct regulator_init_data stamp_avdd_reg_init_data = {
.constraints = {
.name = "2V5",
.valid_ops_mask = REGULATOR_CHANGE_STATUS,
},
.consumer_supplies = ad5624_consumer_supplies,
.num_consumer_supplies = ARRAY_SIZE(ad5624_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 = {
#if defined(CONFIG_AD5624R_SPI) || \
defined(CONFIG_AD5624R_SPI_MODULE)
{
/* the modalias must be the same as spi device driver name */
.modalias = "ad5644r3", /* 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)
Note
The AD5624 Driver depends on CONFIG_SPI
Linux Kernel Configuration
Device Drivers --->
...
<*> Industrial I/O support --->
--- Industrial I/O support
...
Digital to analog converters --->
...
<*> Analog Devices AD5624/44/64R DAC spi 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.
root:/> cd /sys/bus/iio/devices/
root:/sys/bus/iio/devices> ls
iio:device0 iio:device0:buffer0:access0 iio:trigger0
iio:device0:buffer0 iio:device0:buffer0:event0
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 3 16:50 name
-rw-r--r-- 1 root root 4096 Jan 3 16:50 out_voltage0_powerdown
--w------- 1 root root 4096 Jan 3 16:50 out_voltage0_raw
-rw-r--r-- 1 root root 4096 Jan 3 16:50 out_voltage1_powerdown
--w------- 1 root root 4096 Jan 3 16:50 out_voltage1_raw
-rw-r--r-- 1 root root 4096 Jan 3 16:50 out_voltage2_powerdown
--w------- 1 root root 4096 Jan 3 16:50 out_voltage2_raw
-rw-r--r-- 1 root root 4096 Jan 3 16:50 out_voltage3_powerdown
--w------- 1 root root 4096 Jan 3 16:50 out_voltage3_raw
-rw-r--r-- 1 root root 4096 Jan 3 16:50 out_voltage_powerdown_mode
-r--r--r-- 1 root root 4096 Jan 3 16:50 out_voltage_powerdown_mode_available
-r--r--r-- 1 root root 4096 Jan 3 16:50 out_voltage_scale
drwxr-xr-x 2 root root 0 Jan 3 16:50 power
lrwxrwxrwx 1 root root 0 Jan 3 16:50 subsystem -> ../../../../../bus/iio
-rw-r--r-- 1 root root 4096 Jan 3 16:50 uevent
Show device name
root:/sys/devices/platform/bfin-spi.0/spi0.3/iio:device0> cat name
ad5644r3
Show scale
Description: scale to be applied to out_voltage0_raw in order to obtain the measured voltage in millivolts.
root:/sys/devices/platform/bfin-spi.0/spi0.3/iio:device0> cat out_voltage_scale
0.076
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.
root:/sys/devices/platform/bfin-spi.0/spi0.3/iio:device0> echo 10000 > out_voltage0_raw
U = out_voltage0_raw * out_voltage_scale = 10000 * 0.076 = 760,00 mV
List available power down modes
/sys/bus/iio/devices/iio:deviceX/out_voltage_powerdown_mode_available
Description: Lists all available output power down modes.
root:/sys/devices/platform/bfin-spi.0/spi0.3/iio:device0> cat out_voltage_powerdown_mode_available
1kohm_to_gnd 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
1kohm_to_gnd |
connected to ground via an 1kOhm resistor |
100kohm_to_gnd |
connected to ground via an 100kOhm resistor |
three_state |
left floating |
For a list of available output power down options read outX_powerdown_mode_available.
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
Enable power down mode on output Y
/sys/bus/iio/devices/iio:deviceX/out_voltageY_powerdown
Description: Writing 1 causes output Y to enter the power down mode specified by the corresponding out_voltageY_powerdown_mode. Clearing returns to normal operation. Y may be suppressed if all outputs are controlled together.
root:/sys/devices/platform/bfin-spi.0/spi0.3/iio:device0> echo 1 > out_voltage0_powerdown
root:/sys/devices/platform/bfin-spi.0/spi0.3/iio:device0> cat out_voltage0_powerdown
1
root:/sys/devices/platform/bfin-spi.0/spi0.3/iio:device0> echo 0 > out_voltage0_powerdown
root:/sys/devices/platform/bfin-spi.0/spi0.3/iio:device0> cat out_voltage0_powerdown
0