This is a Linux industrial I/O (IIO) subsystem driver, targeting single and multi channel serial interface Capacitance to Digital Converters. 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.
Function | File |
---|---|
driver | drivers/staging/iio/cdc/ad7746.c |
include | drivers/staging/iio/cdc/ad7746.h |
Unlike PCI or USB devices, I2C devices are not enumerated at the hardware level. Instead, the software must know which devices are connected on each I2C bus segment, and what address these devices are using. For this reason, the kernel code must instantiate I2C devices explicitly. There are different ways to achieve this, depending on the context and requirements. However the most common method is to declare the I2C devices by bus number.
This method is appropriate when the I2C bus is a system bus, as in many embedded systems, wherein each I2C bus has a number which is known in advance. It is thus possible to pre-declare the I2C devices that inhabit this bus. This is done with an array of struct i2c_board_info, which is registered by calling i2c_register_board_info().
So, to enable such a driver one need only edit the board support file by adding an appropriate entry to i2c_board_info.
For more information see: Documentation/i2c/instantiating-devices.rst
Depending on the converter IC used, you may need to set the I2C_BOARD_INFO name accordingly, matching your part name.
ADI part number | I2C_BOARD_INFO Name |
---|---|
AD7745 | ad7745 |
AD7746 | ad7746 |
AD7747 | ad7747 |
static struct i2c_board_info __initdata board_i2c_board_info[] = { #if defined(CONFIG_AD7746) || defined(CONFIG_AD7746_MODULE) { I2C_BOARD_INFO("ad7746", 0x48), }, #endif };
static int __init board_init(void) { [--snip--] i2c_register_board_info(0, board_i2c_board_info, ARRAY_SIZE(board_i2c_board_info)); [--snip--] return 0; } arch_initcall(board_init);
Configure kernel with “make menuconfig” (alternatively use “make xconfig” or “make qconfig”)
The driver depends on CONFIG_I2C
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 ri ng -*- Enable triggered sampling support [--snip--] *** Analog to digital converters *** <*> Analog Devices AD7745, AD7746 AD7747 capacitive sensor driver [--snip--]
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.
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/i2c-bfin-twi.0/i2c-0/0-0048/iio:device0> ls -l -r--r--r-- 1 root root 4096 Jan 1 11:17 dev -rw-r--r-- 1 root root 4096 Jan 1 11:17 in_capacitance-capacitance_calibbias -rw-r--r-- 1 root root 4096 Jan 1 11:17 in_capacitance-capacitance_scale -rw-r--r-- 1 root root 4096 Jan 1 11:17 in_capacitance0-capacitance2_calibscale -rw-r--r-- 1 root root 4096 Jan 1 11:17 in_capacitance0-capacitance2_offset -r--r--r-- 1 root root 4096 Jan 1 11:17 in_capacitance0-capacitance2_raw --w------- 1 root root 4096 Jan 1 11:17 in_capacitance0_calibbias_calibration -rw-r--r-- 1 root root 4096 Jan 1 11:17 in_capacitance0_calibscale --w------- 1 root root 4096 Jan 1 11:17 in_capacitance0_calibscale_calibration -rw-r--r-- 1 root root 4096 Jan 1 11:19 in_capacitance0_offset -r--r--r-- 1 root root 4096 Jan 1 11:17 in_capacitance0_raw -rw-r--r-- 1 root root 4096 Jan 1 11:17 in_capacitance1-capacitance3_calibscale -rw-r--r-- 1 root root 4096 Jan 1 11:17 in_capacitance1-capacitance3_offset -r--r--r-- 1 root root 4096 Jan 1 11:17 in_capacitance1-capacitance3_raw --w------- 1 root root 4096 Jan 1 11:17 in_capacitance1_calibbias_calibration -rw-r--r-- 1 root root 4096 Jan 1 11:17 in_capacitance1_calibscale --w------- 1 root root 4096 Jan 1 11:17 in_capacitance1_calibscale_calibration -rw-r--r-- 1 root root 4096 Jan 1 11:17 in_capacitance1_offset -r--r--r-- 1 root root 4096 Jan 1 11:17 in_capacitance1_raw -rw-r--r-- 1 root root 4096 Jan 1 11:17 in_capacitance_calibbias -rw-r--r-- 1 root root 4096 Jan 1 11:17 in_capacitance_sampling_frequency -r--r--r-- 1 root root 4096 Jan 1 11:17 in_capacitance_sampling_frequency_available -rw-r--r-- 1 root root 4096 Jan 1 11:17 in_capacitance_scale -r--r--r-- 1 root root 4096 Jan 1 11:17 in_temp0_input -r--r--r-- 1 root root 4096 Jan 1 11:17 in_temp1_input --w------- 1 root root 4096 Jan 1 11:17 in_voltage0_calibscale_calibration -r--r--r-- 1 root root 4096 Jan 1 11:17 in_voltage0_raw -r--r--r-- 1 root root 4096 Jan 1 11:17 in_voltage1_supply_raw -rw-r--r-- 1 root root 4096 Jan 1 11:17 in_voltage_sampling_frequency -r--r--r-- 1 root root 4096 Jan 1 11:17 in_voltage_sampling_frequency_available -rw-r--r-- 1 root root 4096 Jan 1 11:17 in_voltage_scale -rw-r--r-- 1 root root 4096 Jan 1 11:17 in_voltage_supply_scale -r--r--r-- 1 root root 4096 Jan 1 11:17 name drwxr-xr-x 2 root root 0 Jan 1 11:17 power lrwxrwxrwx 1 root root 0 Jan 1 11:17 subsystem -> ../../../../../../bus/iio -rw-r--r-- 1 root root 4096 Jan 1 11:17 uevent
This specifies any shell prompt running on the target
root:/sys/devices/platform/i2c-bfin-twi.0/i2c-0/0-0048/iio:device0> cat name ad7746
This specifies any shell prompt running on the target
root:/sys/devices/platform/i2c-bfin-twi.0/i2c-0/0-0048/iio:device0> cat in_capacitance_sampling_frequency_available 91 84 50 26 16 13 11 9 root:/sys/devices/platform/i2c-bfin-twi.0/i2c-0/0-0048/iio:device0> cat in_voltage_sampling_frequency_available 50 31 16 8 root:/sys/devices/platform/i2c-bfin-twi.0/i2c-0/0-0048/iio:device0>
This specifies any shell prompt running on the target
root:/sys/devices/platform/i2c-bfin-twi.0/i2c-0/0-0048/iio:device0> cat in_capacitance_sampling_frequency 91 root:/sys/devices/platform/i2c-bfin-twi.0/i2c-0/0-0048/iio:device0> echo 50 > in_capacitance_sampling_frequency root:/sys/devices/platform/i2c-bfin-twi.0/i2c-0/0-0048/iio:device0> cat in_capacitance_sampling_frequency 50 root:/sys/devices/platform/i2c-bfin-twi.0/i2c-0/0-0048/iio:device0>
Lists all available scales for the input and input pairs:
ADC Input | Channel name |
---|---|
CIN1(+) | in_capacitance_scale |
CIN2(+) | in_capacitance_scale |
CIN1(+) - CIN1(-) | in_capacitance-capacitance_scale |
CIN2(+) - CIN2(-) | in_capacitance-capacitance_scale |
VIN1 | in_voltage_scale |
VIN_VDD_MON | in_voltage_supply_scale |
This specifies any shell prompt running on the target
root:/sys/devices/platform/i2c-bfin-twi.0/i2c-0/0-0048/iio:device0> cat in_capacitance_scale 0.000000488
Description:
Raw unscaled capacitance measurement on channel in_capacitance0_raw
ADC Input | Channel name |
---|---|
CIN1(+) | in_capacitance0_raw |
CIN2(+) | in_capacitance1_raw |
CIN1(+) - CIN1(-) | in_capacitance0-capacitance2_raw |
CIN2(+) - CIN2(-) | in_capacitance1-capacitance3_raw |
VIN1 | in_voltage0_raw |
VIN_VDD_MON | in_voltage1_supply_raw |
This specifies any shell prompt running on the target
root:/sys/devices/platform/i2c-bfin-twi.0/i2c-0/0-0048/iio:device0> cat in_capacitance0_raw 14914
U = in_capacitance0_raw * in_capacitance_scale = 14914 * 0.000000488 = 0.007278032 pF
Description:
Scaled temperature measurement on channel in_temp0_input. Results are in millidegrees Celsius.
ADC Input Channel | Channel name |
---|---|
TEMP (internal sensor) | in_temp0_input |
TEMP (external sensor diode) | in_temp1_input |
This specifies any shell prompt running on the target
root:/sys/devices/platform/i2c-bfin-twi.0/i2c-0/0-0048/iio:device0> cat in_temp0_input 28756
T = in_temp0_input = 28756 = 28.756 °C
Description:
If known for a device, offset to be added to <type>[Y]_raw prior
to scaling by <type>[Y]_scale in order to obtain value in the
<type> units as specified in <type>[y]_raw documentation.
Input | CAPDAC | Channel name |
---|---|---|
CIN1(+) | CAPDAC(+) | in_capacitance0_offset |
CIN2(+) | CAPDAC(+) | in_capacitance1_offset |
CIN1(-) | CAPDAC(-) | in_capacitance1-capacitance3_offset |
CIN2(-) | CAPDAC(-) | in_capacitance0-capacitance2_offset |
The AD7745/AD7746 CDC full-scale input range is ±4.096 pF. The part can accept a higher capacitance on the input and the common-mode or offset (not-changing component) capacitance can be balanced by programmable on-chip CAPDACs.
Example 4pF Offset:
in_capacitance0_offset = Offset / in_capacitance_scale = 4pF / 0.000000488 = 8196721
This specifies any shell prompt running on the target
root:/sys/devices/platform/i2c-bfin-twi.0/i2c-0/0-0048/iio:device0> echo 8196721 > in_capacitance0_offset root:/sys/devices/platform/i2c-bfin-twi.0/i2c-0/0-0048/iio:device0> cat in_capacitance0_offset 8127504
Description:
Triggers gain calibration on channel in_capacitance0 or in_capacitance1
This specifies any shell prompt running on the target
root:/sys/devices/platform/i2c-bfin-twi.0/i2c-0/0-0048/iio:device0> echo 1 > in_capacitance1_calibscale_calibration root:/sys/devices/platform/i2c-bfin-twi.0/i2c-0/0-0048/iio:device0> cat in_capacitance1_calibscale 1.000000
Description:
Write gain coefficient for channel in_capacitance0 or in_capacitance1
Valid range is between 1.0 and 1.99999999.
This specifies any shell prompt running on the target
root:/sys/devices/platform/i2c-bfin-twi.0/i2c-0/0-0048/iio:device0> echo 1.5 > in_capacitance1_calibscale root:/sys/devices/platform/i2c-bfin-twi.0/i2c-0/0-0048/iio:device0> cat in_capacitance1_calibscale 1.500000
Description:
Triggers offset calibration on channel in_capacitance0 or in_capacitance1
This specifies any shell prompt running on the target
root:/sys/devices/platform/i2c-bfin-twi.0/i2c-0/0-0048/iio:device0> echo 1 > in_capacitance1_calibbias_calibration root:/sys/devices/platform/i2c-bfin-twi.0/i2c-0/0-0048/iio:device0> cat in_capacitance_calibbias 0