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.
| Function | File |
|---|---|
| driver | drivers/iio/dac/ad5064.c |
Below example specifies a 2.5 Volt reference for the SPI device 3 on SPI-Bus 0. (spi0.3) In this example all 4 reference voltage are supplied by the same regulator.
#if defined(CONFIG_REGULATOR_FIXED_VOLTAGE) || defined(CONFIG_REGULATOR_FIXED_VOLTAGE_MODULE)
static struct regulator_consumer_supply ad5064_consumer_supplies[] = {
REGULATOR_SUPPLY("vrefA", "spi0.3"),
REGULATOR_SUPPLY("vrefB", "spi0.3"),
REGULATOR_SUPPLY("vrefC", "spi0.3"),
REGULATOR_SUPPLY("vrefD", "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: Documentation/spi/spi-summary.rst
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_AD5064_SPI) || \
defined(CONFIG_AD5064_SPI_MODULE)
{
/* the modalias must be the same as spi device driver name */
.modalias = "ad5064", /* 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);
Configure kernel with “make menuconfig” (alternatively use “make xconfig” or “make qconfig”)
The AD5064 Driver depends on CONFIG_SPI
Linux Kernel Configuration
Device Drivers --->
...
<*> Industrial I/O support --->
--- Industrial I/O support
...
Digital to analog converters --->
...
<*> Analog Devices AD5064 and similar multi-channel DAC driver
...
...
...
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.
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 1 03:29 dev
-r--r--r-- 1 root root 4096 Jan 1 03:29 name
-rw-r--r-- 1 root root 4096 Jan 1 03:29 out_voltage0_powerdown
-rw-r--r-- 1 root root 4096 Jan 1 03:29 out_voltage0_powerdown_mode
-rw-r--r-- 1 root root 4096 Jan 1 03:29 out_voltage0_raw
-rw-r--r-- 1 root root 4096 Jan 1 03:29 out_voltage0_scale
-rw-r--r-- 1 root root 4096 Jan 1 03:29 out_voltage1_powerdown
-rw-r--r-- 1 root root 4096 Jan 1 03:29 out_voltage1_powerdown_mode
-rw-r--r-- 1 root root 4096 Jan 1 03:29 out_voltage1_raw
-rw-r--r-- 1 root root 4096 Jan 1 03:29 out_voltage1_scale
-rw-r--r-- 1 root root 4096 Jan 1 03:29 out_voltage2_powerdown
-rw-r--r-- 1 root root 4096 Jan 1 03:29 out_voltage2_powerdown_mode
-rw-r--r-- 1 root root 4096 Jan 1 03:29 out_voltage2_raw
-rw-r--r-- 1 root root 4096 Jan 1 03:29 out_voltage2_scale
-rw-r--r-- 1 root root 4096 Jan 1 03:29 out_voltage3_powerdown
-rw-r--r-- 1 root root 4096 Jan 1 03:29 out_voltage3_powerdown_mode
-rw-r--r-- 1 root root 4096 Jan 1 03:29 out_voltage3_raw
-rw-r--r-- 1 root root 4096 Jan 1 03:29 out_voltage3_scale
-r--r--r-- 1 root root 4096 Jan 1 03:29 out_voltage_powerdown_mode_available
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
The number of channels depends on the chip model.
This specifies any shell prompt running on the target
root:/sys/devices/platform/bfin-spi.0/spi0.3/iio:device0> **cat name**
ad5064
Description:
/sys/bus/iio/devices/iio:deviceX/out_voltageY_scale
scale to be applied to out_voltage0_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_voltage0_scale**
0.038140
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 * 0,038140 mV = 381,14 mV
/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**
1kohm_to_gnd 100kohm_to_gnd three_state
/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 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
/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.
This specifies any shell prompt running on the target
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
The PMOD-DA4 is a PMOD board made by Digilent Inc. which features the AD5628
The following example shows how to connect the PMOD-DA4 to a Blackfin BF537-STAMP board.
| BF537-STAMP (P9) SPI header | PMOD-DA4 | ||
|---|---|---|---|
| PIN | Function | PIN | Function |
| 2 | (+3.3V) | 6 | VDD |
| 5 | SPI_MOSI | 2 | DIN |
| 8 | SPI_SCK | 4 | SCLK |
| 10 | SPI_SS | 1 | SYNC |
| 20 | GND | 5 | GND |