This version is outdated by a newer approved version.
This version (15 Nov 2012 19:54) was approved by Lars-Peter Clausen.The Previously approved version (05 Sep 2012 14:02) is available.
This version (15 Nov 2012 19:54) was approved by Lars-Peter Clausen.The Previously approved version (05 Sep 2012 14:02) is available.This is an old revision of the document!
Table of Contents
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
Files
| Function | File |
|---|---|
| driver | drivers/staging/iio/frequency/ad9834.c |
| include | drivers/staging/iio/frequency/ad9834.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 volatage may vary between boards and models. The platform_data for the device's “struct device” holds this information.
<source trunk/drivers/staging/iio/dds/ad9834.h:ad9834_platform_data{} c linux-kernel>
/** * 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.rst
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.
<box 100% green|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</box>
Show device name
<box 100% green|shell prompt running on the target>
root:/sys/devices/platform/bfin-spi.0/spi0.3/device0> cat name ad9834</box>
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.
<box 100% green|shell prompt running on the target>
root:/sys/devices/platform/bfin-spi.0/spi0.3/device0> cat dds0_freq_scale 1</box>
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.
<box 100% green|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</box>
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.
<box 100% green|shell prompt running on the target>
root:/sys/devices/platform/bfin-spi.0/spi0.3/device0> cat dds0_phase_scale 0.0015339808</box>
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.
<box 100% green|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</box>
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.
<box 100% green|shell prompt running on the target>
root:/sys/devices/platform/bfin-spi.0/spi0.3/device0> cat dds0_out0_wavetype_available sine triangle</box>
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.
<box 100% green|shell prompt running on the target>
root:/sys/devices/platform/bfin-spi.0/spi0.3/device0> echo sine > dds0_out0_wavetype</box>
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).
<box 100% green|shell prompt running on the target>
root:/sys/devices/platform/bfin-spi.0/spi0.3/device0> echo 0 > dds0_pincontrol_en</box>
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.
<box 100% green|shell prompt running on the target>
root:/sys/devices/platform/bfin-spi.0/spi0.3/device0> echo 1 > dds0_out_enable</box>
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.
<box 100% green|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></box>
More Information
- IIO mailing list: linux [dash] iio [at] vger [dot] kernel [dot] org
resources/tools-software/linux-drivers/iio-dds/ad9834.1353005626.txt.gz · Last modified: 15 Nov 2012 19:53 by Lars-Peter Clausen