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This version (06 Jun 2014 15:19) was approved by larsc.The Previously approved version (06 Feb 2014 11:24) is available.Diff

AD5755 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 Yes

Files

Function File
driver drivers/iio/dac/ad5755.c

Example platform device initialization

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 defined(CONFIG_AD5755_SPI) || \
 	defined(CONFIG_AD5755_SPI_MODULE)
	{
		/* the modalias must be the same as spi device driver name */
		.modalias = "ad5755", /* 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,
	},
#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 AD5755 Driver depends on CONFIG_SPI

Linux Kernel Configuration
    Device Drivers  --->
        ...
        <*>     Industrial I/O support --->
            --- Industrial I/O support
            ...
            Digital to analog converters  ---> 
                ...
                <*>  Analog Devices AD5755/AD5755-1/AD5757/AD5735/AD5737 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_current0_calibbias
-rw-r--r--    1 root     root          4096 Jan  2 21:54 out_current0_calibscale
-rw-r--r--    1 root     root          4096 Jan  2 21:54 out_current0_offset
-rw-r--r--    1 root     root          4096 Jan  2 21:54 out_current0_raw
-rw-r--r--    1 root     root          4096 Jan  2 21:54 out_current0_scale
-rw-r--r--    1 root     root          4096 Jan  2 21:54 out_current0_powerdown
-rw-r--r--    1 root     root          4096 Jan  2 21:54 out_current1_calibbias
-rw-r--r--    1 root     root          4096 Jan  2 21:54 out_current1_calibscale
-rw-r--r--    1 root     root          4096 Jan  2 21:54 out_current1_offset
-rw-r--r--    1 root     root          4096 Jan  2 21:54 out_current1_raw
-rw-r--r--    1 root     root          4096 Jan  2 21:54 out_current1_scale
-rw-r--r--    1 root     root          4096 Jan  2 21:54 out_current1_powerdown
-rw-r--r--    1 root     root          4096 Jan  2 21:54 out_voltage2_calibbias
-rw-r--r--    1 root     root          4096 Jan  2 21:54 out_voltage2_calibscale
-rw-r--r--    1 root     root          4096 Jan  2 21:54 out_voltage2_offset
-rw-r--r--    1 root     root          4096 Jan  2 21:54 out_voltage2_raw
-rw-r--r--    1 root     root          4096 Jan  2 21:54 out_voltage2_scale
-rw-r--r--    1 root     root          4096 Jan  2 21:54 out_voltage2_powerdown
-rw-r--r--    1 root     root          4096 Jan  2 21:54 out_voltage3_calibbias
-rw-r--r--    1 root     root          4096 Jan  2 21:54 out_voltage3_calibscale
-rw-r--r--    1 root     root          4096 Jan  2 21:54 out_voltage3_offset
-rw-r--r--    1 root     root          4096 Jan  2 21:54 out_voltage3_raw
-rw-r--r--    1 root     root          4096 Jan  2 21:54 out_voltage3_scale
-rw-r--r--    1 root     root          4096 Jan  2 21:54 out_voltage3_powerdown
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
ad5755

Show scale

Description:
/sys/bus/iio/devices/iio:deviceX/out_voltageY_scale
/sys/bus/iio/devices/iio:deviceX/out_currentY_scale

scale to be applied to out_voltageY_raw/out_currentY_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_voltage2_scale
TBD
root:/sys/devices/platform/bfin-spi.0/spi0.3/iio:device0> cat out_current0_scale
0.000244100

Show offset

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

Raw offset to be applied to out_voltageY_raw in order to obtain the measured voltage in millivolts. The offset is applied before scale is applied.

This specifies any shell prompt running on the target

root:/sys/devices/platform/bfin-spi.0/spi0.3/iio:device0> cat out_voltage2_offset
-TBD
root:/sys/devices/platform/bfin-spi.0/spi0.3/iio:device0> cat out_current0_offset
16384

Set channel Y output voltage

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

Raw (unscaled, no bias etc.) output voltage/current 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_voltage2_raw

U = (out_voltage2_raw + out_voltage2_offset) * out_voltage2_scale = (10000 - TBD) * 0,038140 mV = TBD mV
I = (out_current0_raw + out_current0_offset) * out_current0_scale = (10000 + 16384) * 0,000244100 mV = 6.4403344 mA

Calibrate channel Y gain

Description:
/sys/bus/iio/devices/iio:deviceX/out_voltageY_calibscale
/sys/bus/iio/devices/iio:deviceX/out_currentY_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 65535, minium value is 0, maximum value is 65535.

If scale calibration is used the following formula can be used calculate the output voltage: U = ( ( ( out_voltageY_raw + out_voltageY_offset ) * ( out_voltageY_calibscale + 1 ) ) / 2^16 + out_voltageY_calibbias ) * out_voltageY_scale

Calibrate channel Y offset

Description:
/sys/bus/iio/devices/iio:deviceX/out_voltageY_calibbias
/sys/bus/iio/devices/iio:deviceX/out_currentY_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, minium value is -32768, maximum value is 32767.

If offset calibration is used the following formula can be used calculate the output voltage: U = ( ( ( out_voltageY_raw + out_voltageY_offset ) * ( out_voltageY_calibscale + 1 ) ) / 2^16 + out_voltageY_calibbias ) * out_voltageY_scale

Enable power down mode for the device

/sys/bus/iio/devices/iio:deviceX/out_voltageY_powerdown /sys/bus/iio/devices/iio:deviceX/out_currentY_powerdown

Description:
Writing 1 causes channel Y 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_voltage2_powerdown
root:/sys/devices/platform/bfin-spi.0/spi0.3/iio:device0> cat out_voltage2_powerdown
1
root:/sys/devices/platform/bfin-spi.0/spi0.3/iio:device0> echo 0 > out_voltage2_powerdown
root:/sys/devices/platform/bfin-spi.0/spi0.3/iio:device0> cat out_voltage2_powerdown
0

More Information