This version is outdated by a newer approved version.
This version (14 Oct 2011 10:47) is a draft.
Approvals: 0/1The Previously approved version (26 Aug 2011 22:56) is available.
This version (14 Oct 2011 10:47) is a draft.Approvals: 0/1The Previously approved version (26 Aug 2011 22:56) is available.
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Table of Contents
AD5504 IIO High Voltage ADC Linux Driver
Supported Devices
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
Files
| Function | File |
|---|---|
| driver | drivers/staging/iio/dac/ad5504.c |
| include | drivers/staging/iio/dac/ad5504.h |
Example platform device initialization
For compile time configuration, it’s common Linux practice to keep board- and application-specific configuration out of the main driver file, instead putting it into the board support file.
For devices on custom boards, as typical of embedded and SoC-(system-on-chip) based hardware, Linux uses platform_data to point to board-specific structures describing devices and how they are connected to the SoC. This can include available ports, chip variants, preferred modes, default initialization, additional pin roles, and so on. This shrinks the board-support packages (BSPs) and minimizes board and application specific #ifdefs in drivers.
The reference voltage may vary between boards and models. The platform_data for the device's “struct device” holds this information.
static struct ad5504_platform_data ad5504_pdata = { .vref_mv = 30000, };
This driver supports also an alternative way of specifying the reference voltage, by using the Linux regulator framework.
Specifying reference voltage via the regulator framework
Below example specifies a 30 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 ad5504_consumer_supplies[] = { REGULATOR_SUPPLY("vcc", "spi0.3"), }; static struct regulator_init_data stamp_avdd_reg_init_data = { .constraints = { .name = "30V0", .valid_ops_mask = REGULATOR_CHANGE_STATUS, }, .consumer_supplies = ad5504_consumer_supplies, .num_consumer_supplies = ARRAY_SIZE(ad5504_consumer_supplies), }; static struct fixed_voltage_config stamp_vdd_pdata = { .supply_name = "board-30V0", .microvolts = 30000000, .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);
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.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_AD5504) || \ defined(CONFIG_AD5504_MODULE) { /* the modalias must be the same as spi device driver name */ .modalias = "ad5504", /* 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, .irq = IRQ_PF2, }, #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 AD5504 Driver depends on CONFIG_SPI
Linux Kernel Configuration Device Drivers ---> [*] Staging drivers ---> <*> Industrial I/O support ---> --- Industrial I/O support -*- Enable ring buffer support within IIO -*- Industrial I/O lock free software ring -*- Enable triggered sampling support *** Digital to analog convertors *** [--snip--] <*> Analog Devices AD5504/AD5501 DAC spi driver [--snip--]
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.
<box 100% green|shell prompt running on the target>
root:/> cd /sys/bus/iio/devices/ root:/sys/bus/iio/devices> ls iio:device0 iio:device0: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 14:39 name -rw-r--r-- 1 root root 4096 Jan 3 14:39 out_voltage0_powerdown -rw-r--r-- 1 root root 4096 Jan 3 14:39 out_voltage0_raw -rw-r--r-- 1 root root 4096 Jan 3 14:39 out_voltage1_powerdown -rw-r--r-- 1 root root 4096 Jan 3 14:39 out_voltage1_raw -rw-r--r-- 1 root root 4096 Jan 3 14:39 out_voltage2_powerdown -rw-r--r-- 1 root root 4096 Jan 3 14:39 out_voltage2_raw -rw-r--r-- 1 root root 4096 Jan 3 14:39 out_voltage3_powerdown -rw-r--r-- 1 root root 4096 Jan 3 14:39 out_voltage3_raw -rw-r--r-- 1 root root 4096 Jan 3 14:39 out_voltage_powerdown_mode -r--r--r-- 1 root root 4096 Jan 3 14:39 out_voltage_powerdown_mode_available -r--r--r-- 1 root root 4096 Jan 3 14:39 out_voltage_scale lrwxrwxrwx 1 root root 0 Jan 3 14:39 subsystem -> ../../../../../bus/iio -rw-r--r-- 1 root root 4096 Jan 3 14:39 uevent</box>
Show device name
<box 100% green|shell prompt running on the target>
root:/sys/devices/platform/bfin-spi.0/spi0.3/iio:device0> cat name ad5504</box>
Show scale
Description:
scale to be applied to out_voltage0_raw in order to obtain the measured voltage in millivolts.
<box 100% green|shell prompt running on the target>
root:/sys/devices/platform/bfin-spi.0/spi0.3/iio:device0> cat out_voltage_scale 7.324</box>
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.
<box 100% green|shell prompt running on the target>
root:/sys/devices/platform/bfin-spi.0/spi0.3/iio:device0> echo 1234 > out0_raw</box>
U = out_voltage0_raw * out_voltage_scale = 1234 * 7.324 = 9037,816 mV
List available power down modes
/sys/bus/iio/devices/deviceX/out_voltage_powerdown_mode_available
Description:
Lists all available output power down modes.
<box 100% green|shell prompt running on the target>
root:/sys/devices/platform/bfin-spi.0/spi0.3/iio:device0> cat out_voltage_powerdown_mode_available 20kohm_to_gnd three_state</box>
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
| 20kohm_to_gnd | connected to ground via an 20kOhm resistor |
| three_state | left floating |
For a list of available output power down options read out_voltageX_powerdown_mode_available.
<box 100% green|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</box>
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.
<box 100% green|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</box>
More Information
- IIO mailing list: linux [dash] iio [at] vger [dot] kernel [dot] org
resources/tools-software/linux-drivers/iio-dac/ad5504.1318582042.txt.gz · Last modified: 14 Oct 2011 10:47 by Lars-Peter Clausen