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This version (26 Oct 2012 14:21) was approved by larsc.The Previously approved version (24 Jul 2012 16:29) is available.Diff

ADAS1000: Low Power, 5-ELECTRODE ELECTROCARDIOGRAM (ECG) ANALOG FRONT END (AFE) Linux Driver

Supported Devices

Evaluation Boards

Description

This is a Linux industrial I/O (IIO) subsystem driver, targeting multi channel serial interface ADCs. 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

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
/**
 * struct adas1000_platform_data - ADAS1000 platform data
 * @enbale_vref_buffer: If true enable the vref buffer
 * @use_external_clock: If true use the external clock applied at the XTAL pin
 * @driver_external_common_mode: If true drive the internal common mode signal
 *  to the external common mode pin.
 * @use_external_common_mode: If true use the signal applied at the external
 *  common mode pin as the common mode signal.
 * @high_perfomance: If true configure the ADAS1000 for high performance mode.
 **/
struct adas1000_platform_data {
	bool enable_vref_buffer;
	bool use_external_clock;
	bool drive_external_common_mode;
	bool use_external_common_mode;
	bool high_performance;
};
static struct adas1000_platform_data pdata {
	.enable_vref_buffer = true,
	.high_performance = true,
};

If no platform data is provided the driver will use the device's default setting for all registers.

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 = {
	{
		.modalias = "adas1000",
		.max_speed_hz = 10000000,     /* max spi clock (SCK) speed in HZ */
		.bus_num = 0,
		.chip_select = GPIO_PF10 + MAX_CTRL_CS, /* CS, change it for your board */
		.platform_data = &adas1000_pdata,
		.mode = SPI_MODE_0,
	},
};
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 ADAS1000 Driver depends on CONFIG_SPI

Linux Kernel Configuration
	Device Drivers  --->
		<*>     Industrial I/O support --->
			--- Industrial I/O support
			[--snip--]
			Analog to digital converters  --->  
				*** Analog to digital converters ***
				[--snip--]
				<*> Analog Devices ADAS1000 ECG 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
iio:device0          trigger0

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

root:/sys/devices/platform/bfin-spi.0/spi0.12/iio:device0> ls -l
drwxr-xr-x    2 root     root             0 Jan  1 00:00 buffer
-r--r--r--    1 root     root          4096 Jan  1 00:00 dev
-rw-r--r--    1 root     root          4096 Jan  1 00:00 in_voltage-voltage_filter_low_pass_3db_frequency
-r--r--r--    1 root     root          4096 Jan  1 00:00 in_voltage-voltage_filter_low_pass_3db_frequency_available
-rw-r--r--    1 root     root          4096 Jan  1 00:00 in_voltage-voltage_offset
-rw-r--r--    1 root     root          4096 Jan  1 00:00 in_voltage-voltage_sampling_frequency
-r--r--r--    1 root     root          4096 Jan  1 00:00 in_voltage-voltage_sampling_frequency_available
-rw-r--r--    1 root     root          4096 Jan  1 00:00 in_voltage-voltage_scale
-r--r--r--    1 root     root          4096 Jan  1 00:00 in_voltage-voltage_scale_available
-rw-r--r--    1 root     root          4096 Jan  1 00:00 in_voltage0-voltage2_calibscale
-rw-r--r--    1 root     root          4096 Jan  1 00:00 in_voltage0-voltage5_calibscale
-rw-r--r--    1 root     root          4096 Jan  1 00:00 in_voltage1-voltage0_calibscale
-rw-r--r--    1 root     root          4096 Jan  1 00:00 in_voltage1-voltage2_calibscale
-rw-r--r--    1 root     root          4096 Jan  1 00:00 in_voltage1-voltage5_calibscale
-rw-r--r--    1 root     root          4096 Jan  1 00:00 in_voltage2-voltage5_calibscale
-rw-r--r--    1 root     root          4096 Jan  1 00:00 in_voltage3-voltage5_calibscale
-rw-r--r--    1 root     root          4096 Jan  1 00:00 in_voltage4-voltage5_calibscale
-r--r--r--    1 root     root          4096 Jan  1 00:00 name
-rw-r--r--    1 root     root          4096 Jan  1 00:00 out_voltage6_calibration_offset
-rw-r--r--    1 root     root          4096 Jan  1 00:00 out_voltage6_calibration_powerdown
-rw-r--r--    1 root     root          4096 Jan  1 00:00 out_voltage6_calibration_raw
-rw-r--r--    1 root     root          4096 Jan  1 00:00 out_voltage6_calibration_scale
drwxr-xr-x    2 root     root             0 Jan  1 00:00 power
-rw-r--r--    1 root     root          4096 Jan  1 00:00 rld_out_select
-r--r--r--    1 root     root          4096 Jan  1 00:00 rld_out_select_available
-rw-r--r--    1 root     root          4096 Jan  1 00:00 rld_powerdown
-rw-r--r--    1 root     root          4096 Jan  1 00:00 rld_summing_junction_ce_en
-rw-r--r--    1 root     root          4096 Jan  1 00:00 rld_summing_junction_la_en
-rw-r--r--    1 root     root          4096 Jan  1 00:00 rld_summing_junction_ll_en
-rw-r--r--    1 root     root          4096 Jan  1 00:00 rld_summing_junction_ra_en
-rw-r--r--    1 root     root          4096 Jan  1 00:00 rld_summing_junction_v1_en
-rw-r--r--    1 root     root          4096 Jan  1 00:00 rld_summing_junction_v2_en
drwxr-xr-x    2 root     root             0 Jan  1 00:00 scan_elements
-rw-r--r--    1 root     root          4096 Jan  1 00:00 shield_driver_powerdown
lrwxrwxrwx    1 root     root             0 Jan  1 00:00 subsystem -> ../../../../../../../bus/iio
drwxr-xr-x    2 root     root             0 Jan  1 00:00 trigger
-rw-r--r--    1 root     root          4096 Jan  1 00:00 uevent
-rw-r--r--    1 root     root          4096 Jan  1 00:00 vcm_summing_junction_ce_en
-rw-r--r--    1 root     root          4096 Jan  1 00:00 vcm_summing_junction_la_en
-rw-r--r--    1 root     root          4096 Jan  1 00:00 vcm_summing_junction_ll_en
-rw-r--r--    1 root     root          4096 Jan  1 00:00 vcm_summing_junction_ra_en
-rw-r--r--    1 root     root          4096 Jan  1 00:00 vcm_summing_junction_v1_en
-rw-r--r--    1 root     root          4096 Jan  1 00:00 vcm_summing_junction_v2_en

root:/sys/devices/platform/bfin-spi.0/spi0.12/iio:device0>

Show device name

This specifies any shell prompt running on the target

root:/sys/devices/platform/bfin-spi.0/spi_master/spi0/spi0.18/iio:device0/> cat name
adas1000

Contains the device name, this will always be “adas1000” for the adas1000 driver.

List available low filter frequencies

Description:
in_voltage-voltage_filter_low_pass_3db_frequency_available

Lists all available low pass filter frequencies, which may be set by writing to in_voltage-voltage_filter_low_pass_3db_frequency.

This specifies any shell prompt running on the target

root:/sys/devices/platform/bfin-spi.0/spi0.3/device0> cat in_voltage-voltage_filter_low_pass_3db_frequency_available
40 150 250 400
root:/sys/devices/platform/bfin-spi.0/spi0.3/device0>

Set and show low filter frequency

Description:
in_voltage-voltage_filter_low_pass_3db_frequency

Writing to this file will set the low pass filter frequency, reading from this file will show the currently selected low pass filter.

This specifies any shell prompt running on the target

root:/sys/devices/platform/bfin-spi.0/spi0.3/device0> cat in_voltage-voltage_filter_low_pass_3db_frequency
40
root:/sys/devices/platform/bfin-spi.0/spi0.3/device0> echo 250 > in_voltage-voltage_filter_low_pass_3db_frequency
root:/sys/devices/platform/bfin-spi.0/spi0.3/device0> cat in_voltage-voltage_filter_low_pass_3db_frequency
250
root:/sys/devices/platform/bfin-spi.0/spi0.3/device0>

The low pass filter will only be active when sampling with 2kHz base frequency.

List available sampling frequencies

Description:
in_voltage-voltage_sampling_frequency_available

Lists all available sampling frequencies, which may be set by writing to in_voltage-voltage_sampling_frequency.

This specifies any shell prompt running on the target

root:/sys/devices/platform/bfin-spi.0/spi0.3/device0> cat in_voltage-voltage_sampling_frequency_available
128000 64000 32000 16000 8000 4000 2000 1000 500
root:/sys/devices/platform/bfin-spi.0/spi0.3/device0>

The only actuall supported sampling rates by the ADAS1000 are 128000, 16000 and 2000, all other sampling rates will be achieved by using a 2x or 4x decimation filter.

Set and show filter frequency

Description:
in_voltage-voltage_sampling_frequency

Writing to this file will set the sampling frequency, reading from the file will return the currently selected sampling frequency.

This specifies any shell prompt running on the target

root:/sys/devices/platform/bfin-spi.0/spi0.3/device0> cat in_voltage-voltage_sampling_frequency
4000
root:/sys/devices/platform/bfin-spi.0/spi0.3/device0>

Setting a new sampling frequency can be done by writing to the file.

This specifies any shell prompt running on the target

root:/sys/devices/platform/bfin-spi.0/spi0.3/device0> echo 8000 > in_voltage-voltage_sampling_frequency
root:/sys/devices/platform/bfin-spi.0/spi0.3/device0> cat in_voltage-voltage_sampling_frequency
8000
root:/sys/devices/platform/bfin-spi.0/spi0.3/device0>

List available ADC gain values

Description:
in_voltage-voltage_scale_available

List the available ADC gain settings, which can be set using in_voltage-voltage_scale.

This specifies any shell prompt running on the target

root:/sys/devices/platform/bfin-spi.0/spi0.3/device0> cat in_voltage-voltage_scale_available
0.000019618 0.000013079 0.000009809 0.000006539
root:/sys/devices/platform/bfin-spi.0/spi0.3/device0>

Set and ADC gain value

Description:
in_voltage-voltage_scale

Scale to be applied to in_voltageY-voltageZ_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/device0> cat in_voltage-voltage_scale
0.000019618
root:/sys/devices/platform/bfin-spi.0/spi0.3/device0> echo 0.000006539 > in_voltage-voltage_scale
root:/sys/devices/platform/bfin-spi.0/spi0.3/device0> cat in_voltage-voltage_scale
0.000006539
root:/sys/devices/platform/bfin-spi.0/spi0.3/device0>

Set ADC calibration gain

Description:
in_voltage0-voltage2_calibscale
in_voltage0-voltage5_calibscale
in_voltage1-voltage0_calibscale
in_voltage1-voltage2_calibscale
in_voltage1-voltage5_calibscale
in_voltage2-voltage5_calibscale
in_voltage3-voltage5_calibscale
in_voltage4-voltage5_calibscale

Set the channel calibration gain. Writing to these files will set the calibration gain for the respective channel. Valid values are in the range of -2048 to 2047.

This specifies any shell prompt running on the target

root:/sys/devices/platform/bfin-spi.0/spi0.3/device0> echo 1020 > in_voltage0-voltage2_calibscale
root:/sys/devices/platform/bfin-spi.0/spi0.3/device0> cat in_voltage0-voltage2_calibscale
1020
root:/sys/devices/platform/bfin-spi.0/spi0.3/device0>

in_voltage0-voltage2_calibscale and in_voltage0-voltage5_calibscale, in_voltage1-voltage0_calibscale and in_voltage1-voltage5_calibscale, in_voltage1-voltage2_calibscale and in_voltage2-voltage5_calibscale refer to the same set of calibration data.

List available Right Leg drive outputs

Description:
rld_out_select_available

List available values for the rld_out_select file.

This specifies any shell prompt running on the target

root:/sys/devices/platform/bfin-spi.0/spi0.3/device0> cat rld_out_select_available
rl la ll ra v1 v2
root:/sys/devices/platform/bfin-spi.0/spi0.3/device0>

Select Right Leg drive output electrode

Description:
rld_out_select

Set the Right Leg drive output electrode.

This specifies any shell prompt running on the target

root:/sys/devices/platform/bfin-spi.0/spi0.3/device0> echo rl > rld_out_select_available
root:/sys/devices/platform/bfin-spi.0/spi0.3/device0> cat rld_out_select
rl
root:/sys/devices/platform/bfin-spi.0/spi0.3/device0>

Enable/Disable Right Leg drive output

Description:
rld_powerdown

Enable or disable the Right Leg drive output. Writing a '0' to this file will enable the Right Leg drive, writing a '1' to this file will enable the Right Leg drive.

This specifies any shell prompt running on the target

root:/sys/devices/platform/bfin-spi.0/spi_master/spi0/spi0.18/iio:device0> cat rld_powerdown
1
root:/sys/devices/platform/bfin-spi.0/spi_master/spi0/spi0.18/iio:device0> echo 0 > rld_powerdown
root:/sys/devices/platform/bfin-spi.0/spi_master/spi0/spi0.18/iio:device0> cat rld_powerdown
0

Setup Right Leg drive summing junction configuration

Description:
rld_summing_junction_ce_en
rld_summing_junction_la_en
rld_summing_junction_ll_en
rld_summing_junction_ra_en
rld_summing_junction_v1_en
rld_summing_junction_v2_en

Writing a '1' to a file will add the respective channel to the Right Leg driver summing junction, writing a '0' will remove it.

This specifies any shell prompt running on the target

root:/sys/devices/platform/bfin-spi.0/spi_master/spi0/spi0.18/iio:device0> cat rld_summing_junction_la_en
1
root:/sys/devices/platform/bfin-spi.0/spi_master/spi0/spi0.18/iio:device0> echo 1 > rld_summing_junction_v2_en
root:/sys/devices/platform/bfin-spi.0/spi_master/spi0/spi0.18/iio:device0> cat rld_summing_junction_v2_en
1

Setup VCM summing junction configuration

Description:
vcm_summing_junction_ce_en
vcm_summing_junction_la_en
vcm_summing_junction_ll_en
vcm_summing_junction_ra_en
vcm_summing_junction_v1_en
vcm_summing_junction_v2_en

Writing a '1' to a file will add the respective channel to the VCM summing junction, writing a '0' will remove it.

This specifies any shell prompt running on the target

root:/sys/devices/platform/bfin-spi.0/spi_master/spi0/spi0.18/iio:device0> cat vcm_summing_junction_ra_en
0
root:/sys/devices/platform/bfin-spi.0/spi_master/spi0/spi0.18/iio:device0> echo 1 > vcm_summing_junction_ra_en
root:/sys/devices/platform/bfin-spi.0/spi_master/spi0/spi0.18/iio:device0> cat vcm_summing_junction_ra_en
1

Enable/Disable shield driver

Description:
shield_driver_powerdown

Enable or disable the shield driver. Writing a '0' to this file will enable the shild driver, writing a '1' to this file will enable the shield driver.

This specifies any shell prompt running on the target

root:/sys/devices/platform/bfin-spi.0/spi_master/spi0/spi0.18/iio:device0> cat shield_driver_powerdown
1
root:/sys/devices/platform/bfin-spi.0/spi_master/spi0/spi0.18/iio:device0> echo 0 > shield_driver_powerdown
root:/sys/devices/platform/bfin-spi.0/spi_master/spi0/spi0.18/iio:device0> cat shield_driver_powerdown
0

out_voltage6_calibration_offset

Enable/Disable calibration DAC

Description:
out_voltage6_calibration_powerdown

Enable or disable the calibration DAC. Writing a '0' to this file will enable the calibration DAC, writing a '1' to this file will disable the calibration DAC.

This specifies any shell prompt running on the target

root:/sys/devices/platform/bfin-spi.0/spi_master/spi0/spi0.18/iio:device0> cat out_voltage6_calibration_raw
1
root:/sys/devices/platform/bfin-spi.0/spi_master/spi0/spi0.18/iio:device0> echo 0 > out_voltage6_calibration_powerdown
root:/sys/devices/platform/bfin-spi.0/spi_master/spi0/spi0.18/iio:device0> cat out_voltage6_calibration_raw
0

Set calibration DAC output value

Description:
out_voltage6_calibration_raw

Sets the calibration DAC output value. Valid values are in the range of 0-1023.

This specifies any shell prompt running on the target

root:/sys/devices/platform/bfin-spi.0/spi_master/spi0/spi0.18/iio:device0> echo 100 > out_voltage6_calibration_raw
root:/sys/devices/platform/bfin-spi.0/spi_master/spi0/spi0.18/iio:device0> cat out_voltage6_calibration_raw
100

Show calibration DAC scale

Description:
out_voltage6_calibration_scale

This specifies any shell prompt running on the target

root:/sys/devices/platform/bfin-spi.0/spi_master/spi0/spi0.18/iio:device0> cat out_voltage6_calibration_scale
0.002346

Vout = (out_voltage6_calibration_offset + out_voltage6_calibration_raw) * out_voltage6_calibration_scale

Debugfs

The adas1000 driver exposes also some files, which are meant for debugging purposes, in debugfs. These files can be used to read the OPSTAT register and to configure the testtone generator.

root:/sys/kernel/debug/iio/iio:device0> ls direct_reg_access pll_locked testtone_la_en testtone_v1_en fuse_crc_failure testtone_en testtone_ll_en testtone_v2_en fuse_status testtone_frequency testtone_out_en pll_lock_lost testtone_internal testtone_ra_en root:/sys/kernel/debug/iio/iio:device0>

Direct register read and write acccess

Description:
direct_reg_access

Allows direct register access to the device. To write to a register write the register address and the register value seperated by a space to the file.

This specifies any shell prompt running on the target

root:/sys/kernel/debug/iio/iio:device0> echo 0x12 0x17 > direct_reg_access

To read a register value, first write the register address to the file followed by a read.

This specifies any shell prompt running on the target

root:/sys/kernel/debug/iio/iio:device0> echo 0x05 > direct_reg_access
root:/sys/kernel/debug/iio/iio:device0> cat direct_reg_access

Check fuse CRC status

Description:
fuse_crc_failure

'1' if a fuse CRC failure has been detected, '0' otherwise.

Check fuse status

Description:
fuse_status

'0' if the fuse bits have been read, '1' otherwise.

Check PLL status

Description:
pll_locked

'1' if the PLL is locked, '0' otherwise.

Enable testtone

Description:
testtone_en

Enable the testtone generator.

If both the testtone and the calibration DAC are enabled, the testtone will take precedence.

Set testtone frequnecy

Description:
testtone_frequency

Select the testtone frequency and waveform.

Valid values are:

  • 1: 1 Hz square wave
  • 10: 10 Hz sine wave
  • 150: 150 Hz sine wave

Enable internal testtone routing

Description:
testtone_internal

Route the testtone signal internally ECG channels.

Enable external testtone output

Description:
testtone_out_en

Enables or disables testtone output to the external CAL_DAC_IO pin.

The testtone signal will be routed to the CAL_DAC_IO pin by default and only if internal routing is enabled this switch will have an effect.

Enable testtone routing to individual ECG channels

Description:
testtone_la_en
testtone_ll_en
testtone_ra_en
testtone_v1_en
testtone_v2_en

Enables the internal testtone routing to the individual ECG channels.

Trigger management

The adas1000 driver will register a IIO trigger for the device. The trigger will be hooked up to the devices DATARDY IRQ. Normally you would want to use this trigger as the trigger for the device.

This specifies any shell prompt running on the target

root:/sys/devices/platform/bfin-spi.0/spi_master/spi0/spi0.18/iio:device0/> echo adas1000-dev0 > trigger/current_trigger
root:/sys/devices/platform/bfin-spi.0/spi_master/spi0/spi0.18/iio:device0/> cat trigger/current_trigger 
adas1000-dev0

Buffer management

The Industrial I/O subsystem provides support for various ring buffer based data acquisition methods. Apart from device specific hardware buffer support, the user can chose between two different software ring buffer implementations. One is the IIO lock free software ring, and the other is based on Linux kfifo. Devices with buffer support feature an additional sub-folder in the /sys/bus/iio/devices/deviceX/ folder hierarchy. Called deviceX:bufferY, where Y defaults to 0, for devices with a single buffer.

Every buffer implementation features a set of files:

length
Get/set the number of sample sets that may be held by the buffer.

enable
Enables/disables the buffer. This file should be written last, after length and selection of scan elements.

scan_elements
The scan_elements directory contains interfaces for elements that will be captured for a single triggered sample set in the buffer.

02 Mar 2011 15:16 · Michael Hennerich

This specifies any shell prompt running on the target

root:/sys/devices/platform/bfin-spi.0/spi_master/spi0/spi0.18/iio:device0/scan_elements> ls
in_voltage0-voltage2_en     in_voltage1-voltage5_en
in_voltage0-voltage2_index  in_voltage1-voltage5_index
in_voltage0-voltage2_type   in_voltage1-voltage5_type
in_voltage0-voltage5_en     in_voltage2-voltage5_en
in_voltage0-voltage5_index  in_voltage2-voltage5_index
in_voltage0-voltage5_type   in_voltage2-voltage5_type
in_voltage1-voltage0_en     in_voltage3-voltage5_en
in_voltage1-voltage0_index  in_voltage3-voltage5_index
in_voltage1-voltage0_type   in_voltage3-voltage5_type
in_voltage1-voltage2_en     in_voltage4-voltage5_en
in_voltage1-voltage2_index  in_voltage4-voltage5_index
in_voltage1-voltage2_type   in_voltage4-voltage5_type
root:/sys/devices/platform/bfin-spi.0/spi_master/spi0/spi0.18/iio:device0/scan_elements>

Channel Function
in_voltage0-voltage2 LA-RA (LEAD I)
in_voltage1-voltage0 LL-LA (LEAD II)
in_voltage1-voltage2 LL-RA (LEAD III)
in_voltage0-voltage5 LA-VCM
in_voltage1-voltage5 LL-VCM
in_voltage2-voltage5 RA-VCM
in_voltage3-voltage5 V1-VCM (V1')
in_voltage4-voltage5 V2-VCM (V2')

If any of the first three channels is selected the device will operate in Lead mode, otherwise it will operate in single-end mode. If channels from the first three channels are selected channels from the second three channels can not be selected and vice versa.

in_voltageX_en / in_voltageX-voltageY_en / timestamp_en:
Scan element control for triggered data capture. Writing 1 will enable the scan element, writing 0 will disable it

in_voltageX_type / in_voltageX-voltageY_type / timestamp_type:
Description of the scan element data storage within the buffer and therefore in the form in which it is read from user-space. Form is [s|u]bits/storage-bits. s or u specifies if signed (2's complement) or unsigned. bits is the number of bits of data and storage-bits is the space (after padding) that it occupies in the buffer. Note that some devices will have additional information in the unused bits so to get a clean value, the bits value must be used to mask the buffer output value appropriately. The storage-bits value also specifies the data alignment. So u12/16 will be a unsigned 12 bit integer stored in a 16 bit location aligned to a 16 bit boundary. For other storage combinations this attribute will be extended appropriately.

in_voltageX_index / in_voltageX-voltageY_index / timestamp_index:
A single positive integer specifying the position of this scan element in the buffer. Note these are not dependent on what is enabled and may not be contiguous. Thus for user-space to establish the full layout these must be used in conjunction with all _en attributes to establish which channels are present, and the relevant _type attributes to establish the data storage format.

02 Mar 2011 15:16 · Michael Hennerich

More Information