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AD9834 IIO Direct Digital Synthesis Linux Driver

Supported Devices

Reference Circuits

Evaluation Boards

Description

This is a Linux industrial I/O (IIO) subsystem driver, targeting serial interface DDS controllers. 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

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.

21 Oct 2010 16:10 · Michael Hennerich

The reference volatage may vary between boards and models. The platform_data for the device's “struct device” holds this information.

file: drivers/staging/iio/dds/ad9834.h

scm failed with exit code 1:
file does not exist in git: http://raw.github.com/analogdevicesinc/linux/master/drivers/staging/iio/dds/ad9834.h
/**
 * struct ad9834_platform_data - platform specific information
 * @mclk:		master clock in Hz
 * @freq0:		power up freq0 tuning word in Hz
 * @freq1:		power up freq1 tuning word in Hz
 * @phase0:		power up phase0 value [0..4095] correlates with 0..2PI
 * @phase1:		power up phase1 value [0..4095] correlates with 0..2PI
 * @en_div2:		digital output/2 is passed to the SIGN BIT OUT pin
 * @en_signbit_msb_out:	the MSB (or MSB/2) of the DAC data is connected to the
 *			SIGN BIT OUT pin. en_div2 controls whether it is the MSB
 *			or MSB/2 that is output. if en_signbit_msb_out=false,
 *			the on-board comparator is connected to SIGN BIT OUT
 */
 
struct ad9834_platform_data ad9834_pdata = {
	.mclk = 75000000,
	.freq0 = 1000000,
	.freq1 = 5000000,
	.phase0 = 512,
	.phase1 = 1024,
	.en_div2 = false,
	.en_signbit_msb_out = false,
};

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 DDS 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_AD9834) \
	|| defined(CONFIG_AD9834_MODULE)
	{
		.modalias = "ad9834",
		.max_speed_hz = 1000000,     /* max spi clock (SCK) speed in HZ */
		.bus_num = 0,
		.chip_select = 3, /* CS, change it for your board */
		.platform_data = &ad9834_pdata, /* No spi_driver specific config */
		.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 AD9834 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

			          *** Direct Digital Synthesis ***
			    [--snip--]

			    <*>   Analog Devices ad9833/4/ 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.

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
device0
root:/sys/bus/iio/devices> cd device0

root:/sys/devices/platform/bfin-spi.0/spi0.3/device0> ls -l
--w-------    1 root     root          4096 Jan  3 14:06 dds0_freq0
--w-------    1 root     root          4096 Jan  3 14:06 dds0_freq1
-r--r--r--    1 root     root          4096 Jan  3 14:06 dds0_freq_scale
--w-------    1 root     root          4096 Jan  3 14:06 dds0_freqsymbol
--w-------    1 root     root          4096 Jan  3 14:06 dds0_out0_wavetype
-r--r--r--    1 root     root          4096 Jan  3 14:06 dds0_out0_wavetype_available
--w-------    1 root     root          4096 Jan  3 14:06 dds0_out1_enable
--w-------    1 root     root          4096 Jan  3 14:06 dds0_out1_wavetype
-r--r--r--    1 root     root          4096 Jan  3 14:06 dds0_out1_wavetype_available
--w-------    1 root     root          4096 Jan  3 14:06 dds0_out_enable
--w-------    1 root     root          4096 Jan  3 14:06 dds0_phase0
--w-------    1 root     root          4096 Jan  3 14:06 dds0_phase1
-r--r--r--    1 root     root          4096 Jan  3 14:06 dds0_phase_scale
--w-------    1 root     root          4096 Jan  3 14:06 dds0_phasesymbol
--w-------    1 root     root          4096 Jan  3 14:06 dds0_pincontrol_en
-r--r--r--    1 root     root          4096 Jan  3 14:06 name
drwxr-xr-x    2 root     root             0 Jan  3 14:06 power
lrwxrwxrwx    1 root     root             0 Jan  3 14:06 subsystem -> ../../../../../bus/iio
-rw-r--r--    1 root     root          4096 Jan  3 14:06 uevent

Show device name

This specifies any shell prompt running on the target

root:/sys/devices/platform/bfin-spi.0/spi0.3/device0> cat name
ad9834

Show frequency scale

/sys/bus/iio/devices/…/ddsX_freqY_scale

Scale to be applied to ddsX_freqY in order to obtain the desired value in Hz. If shared across all frequency registers Y is not present. It is also possible X is not present if shared across all channels.

This specifies any shell prompt running on the target

root:/sys/devices/platform/bfin-spi.0/spi0.3/device0> cat dds0_freq_scale
1

Set frequency symbol 0/1

/sys/bus/iio/devices/…/ddsX_freqY

Stores frequency into tuning word Y. There will be more than one ddsX_freqY file, which allows for pin controlled FSK Frequency Shift Keying (ddsX_pincontrol_freq_en is active) or the user can control the desired active tuning word by writing Y to the ddsX_freqsymbol file.

This specifies any shell prompt running on the target

root:/sys/devices/platform/bfin-spi.0/spi0.3/device0> echo 1000000 > dds0_freq0
root:/sys/devices/platform/bfin-spi.0/spi0.3/device0> echo 500000 > dds0_freq0

freq0 = ddsX_freq0 * dds0_freq_scale = 1000000 * 1 = 1 MHz
freq1 = ddsX_freq1 * dds0_freq_scale = 500000 * 1 = 500 kHz

Show phase scale

/sys/bus/iio/devices/…/ddsX_phaseY_scale

Scale to be applied to ddsX_phaseY in order to obtain the desired value in rad. If shared across all phase registers Y is not present. It is also possible X is not present if shared across all channels.

This specifies any shell prompt running on the target

root:/sys/devices/platform/bfin-spi.0/spi0.3/device0> cat dds0_phase_scale
0.0015339808

Set phase symbol 0/1

/sys/bus/iio/devices/…/ddsX_phaseY

Stores phase into Y. There will be more than one ddsX_phaseY file, which allows for pin controlled PSK Phase Shift Keying (ddsX_pincontrol_phase_en is active) or the user can control the desired phase Y which is added to the phase accumulator output by writing Y to the en_phase file.

This specifies any shell prompt running on the target

root:/sys/devices/platform/bfin-spi.0/spi0.3/device0> echo 512 > dds0_phase0
root:/sys/devices/platform/bfin-spi.0/spi0.3/device0> echo 2048 > dds0_phase0

phase0 = dds0_phase0 * ddsX_phaseY_scale = 512 * 0.0015339808 = 0.7853981696 rad
phase1 = dds0_phase1 * ddsX_phaseY_scale = 2048 * 0.0015339808 = PI = 3.1415926 rad

List available wavetypes

/sys/bus/iio/devices/…/ddsX_outY_wavetype_available

Lists all available output waveform options.

This specifies any shell prompt running on the target

root:/sys/devices/platform/bfin-spi.0/spi0.3/device0> cat dds0_out0_wavetype_available
sine triangle

Set wavetype

/sys/bus/iio/devices/…/ddsX_outY_wavetype

Specifies the output waveform. (sine, triangle, ramp, square, …) For a list of available output waveform options read available_output_modes.

This specifies any shell prompt running on the target

root:/sys/devices/platform/bfin-spi.0/spi0.3/device0> echo sine > dds0_out0_wavetype

Disable FSK/PSK pincontrol

/sys/bus/iio/devices/…/ddsX_pincontrol_en

ddsX_pincontrol_en: Both, the active frequency and phase is controlled by the respective phase and frequency control inputs. In case the device in question allows to independent controls, then there are dedicated files (ddsX_pincontrol_freq_en, ddsX_pincontrol_phase_en).

This specifies any shell prompt running on the target

root:/sys/devices/platform/bfin-spi.0/spi0.3/device0> echo 0 > dds0_pincontrol_en

Enable output 0

/sys/bus/iio/devices/…/ddsX_out_enable
/sys/bus/iio/devices/…/ddsX_outY_enable

ddsX_outY_enable controls signal generation on output Y of channel X. Y may be suppressed if all channels are controlled together.

This specifies any shell prompt running on the target

root:/sys/devices/platform/bfin-spi.0/spi0.3/device0> echo 1 > dds0_out_enable

Switch between frequency symbol 0/1

/sys/bus/iio/devices/…/ddsX_freqsymbol

Specifies the active output frequency tuning word. The value corresponds to the Y in ddsX_freqY. To exit this mode the user can write ddsX_pincontrol_freq_en or ddsX_out_enable file.

This specifies any shell prompt running on the target

root:/sys/devices/platform/bfin-spi.0/spi0.3/device0> echo 1 > dds0_freqsymbol
root:/sys/devices/platform/bfin-spi.0/spi0.3/device0> echo 0 > dds0_freqsymbol
root:/sys/devices/platform/bfin-spi.0/spi0.3/device0>

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