IIO (Industrial I / O) is a subsystem of the Linux kernel for analog to digital converters (ADC), digital to analog converters (DAC), and various types of sensors. Can be used on high speed industrial devices. It also includes a built-in API for other drivers.

Industrial I/O Linux ( ) , . , sysfs devfs.

IIO:

IIO :

(: )
- , DFSDM (, , )
, TIM LPTIM
SPI I2C

IIO , , ...

IIO

/ :

# https://www.kernel.org/doc/Documentation/i2c/dev-interface
open("/dev/i2c-1", O_RDWR);
# https://www.kernel.org/doc/Documentation/spi/spidev.rst
open("/dev/spidev2.0", O_RDWR);

, :

— ?

"" ( ).

IIO - , - poll .

IIO — .

IIO

sysfs ( ):

# cat /sys/bus/iio/devices/iio\:device0/in_accel_x_raw
-493

"" , .

read():

#      
(cd /sys/bus/iio/devices/iio:device0/scan_elements/ && for file in *_en; do echo 1 > $file; done)

int fd = open("/dev/iio:device0");
read(fd, buffer, scan_size);
#  scan_size      ,     1  /sys/bus/iio/devices/iio:device0/scan_elements/*_en

scan_size, "" , , .

IIO struct iio_chan_spec:

IIO types

BME280

/* https://elixir.bootlin.com/linux/v5.9-rc1/source/drivers/iio/pressure/bmp280-core.c#L132*/
static const struct iio_chan_spec bmp280_channels[] = {
    {
        .type = IIO_PRESSURE,
        .info_mask_separate = BIT(IIO_CHAN_INFO_PROCESSED) |
                      BIT(IIO_CHAN_INFO_OVERSAMPLING_RATIO),
    },
    {
        .type = IIO_TEMP,
        .info_mask_separate = BIT(IIO_CHAN_INFO_PROCESSED) |
                      BIT(IIO_CHAN_INFO_OVERSAMPLING_RATIO),
    },
    {
        .type = IIO_HUMIDITYRELATIVE,
        .info_mask_separate = BIT(IIO_CHAN_INFO_PROCESSED) |
                      BIT(IIO_CHAN_INFO_OVERSAMPLING_RATIO),
    },
};

, , — .

Linux , .

, kfifo .

, , , .

. , , , , , .

, CLOCK_REALTIME.

IIO Triggered Buffers

"" , user space.

, .

# cat /sys/bus/iio/devices/iio\:device0/trigger/current_trigger
icm20608-dev0
# echo > /sys/bus/iio/devices/iio\:device0/trigger/current_trigger
# cat /sys/bus/iio/devices/iio\:device0/trigger/current_trigger
# echo "icm20608-dev0" > /sys/bus/iio/devices/iio\:device0/trigger/current_trigger

Official Trigger Documentation

IIO sysfs trigger

Industrial IIO configfs support

Triggered buffer support trigger buffer support for IIO subsystem of Linux device driver

Device owned triggers

, device tree:

icm20608: imu@0 {
    ...
    interrupt-parent = <&gpio5>;
    interrupts = <11 IRQ_TYPE_EDGE_RISING>;
    ...
};

cat /sys/bus/iio/devices/trigger0/name
icm20608-dev0

gpio, , .

Interrupt triggers (also known as gpio trigger)

iio-trig-interrupt

, . gpio, .

, maintainer'a IIO Jonathan Cameron, .

— Triggered buffer support trigger buffer support for IIO subsystem of Linux device driver

.

[v3,1/6] dt-bindings: iio: introduce trigger providers, consumers

device tree :

trig0: interrupt-trigger0 {
    #io-trigger-cells = <0>;
    compatible = "interrupt-trigger";
    interrupts = <11 0>;
    interrupt-parent = <&gpioa>;
};

sysfs trigger

iio-trig-sysfs

sysfs — , .

# echo 10 > /sys/bus/iio/devices/iio_sysfs_trigger/add_trigger

"sysfstrig%d", .

High resolution timer trigger

1 .

# mkdir /sys/kernel/config/iio/triggers/hrtimer/my_trigger_name
# cat /sys/bus/iio/devices/trigger4/name
my_trigger_name
# cat /sys/bus/iio/devices/trigger4/sampling_frequency
100

— "" SoC.

loop trigger

iio-trig-loop

PATCH v1 5/5 iio:pressure:ms5611: continuous sampling support

.

. :

iio:trigger: Experimental kthread tight loop trigger.

DT, , .

Device tree

label , , of_node iio:device — /sys/bus/iio/devices/iio\:device0/of_node/.

— https://elixir.bootlin.com/linux/v5.9-rc1/source/Documentation/devicetree/bindings/iio

, IIO, enum iio_chan_type . iio_event_monitor.

IIO iio-buffer-sysfs-interface.

[be|le]:[s|u]bits/storagebitsXrepeat[>>shift]

icm20608:

# cat /sys/bus/iio/devices/iio\:device0/scan_elements/*_type
be:s16/16>>0
be:s16/16>>0
be:s16/16>>0
be:s16/16>>0
be:s16/16>>0
be:s16/16>>0
le:s64/64>>0

le be c
— , s u
/ ,

be:u4/8>>0
be:u4/8>>4

repeat — 1 .

Scaling and offset

/sys/bus/iio/devices/iio:deviceX/in_*_raw
/sys/bus/iio/devices/iio:deviceX/in_*_offset
/sys/bus/iio/devices/iio:deviceX/in_*_scale

(raw + offset)*scale, offset'a .

How to do a simple ADC conversion using the sysfs interface

iio_simple_dummy

iio_simple_dummy — IIO :

IIO_VOLTAGE
IIO_ACCEL
IIO_ACTIVITY

The iio_simple_dummy Anatomy

iio_simple_dummy

libiio

— libiio Analog Devices.

, / .

/, , Linux, Windows Mac , USB, Ethernet Serial.

iiod:

On remote :

host # iiod

On local :

local $ iio_info -n [host_address]
local $ iio_attr -u ip:[host_address] -d
local $ iio_readdev -u ip:[host_address] -b 256 -s 0 icm20608

Matlab, .

, libiio .

https://github.com/maquefel/icm20608-iio

libiio

sysfs , :

, /sys/bus/iio/iio:deviceN/name, /sys/bus/iio/iio:deviceN /dev/iio:deviceN
/sys/bus/iio/iio:deviceN/scan_elements/, , *_en
/sys/bus/iio/iio:deviceN/enable

E libiio.

https://elixir.bootlin.com/linux/v5.9-rc1/source/drivers/iio/industrialio-buffer.c#L574

    # bytes -      
    # length -    
    # offset -        
    if (bytes % length == 0)
        offset = bytes;
    else
        offset = bytes - bytes % length + length;

    bytes = offset + length;

libiio, :

, (Sign extension)
offset,
scale,

    input = is_be ? betoh(input) : letoh(input);
    input >>= shift;
    input &= BIT_MASK(bits);
    value = is_signed ? (float)sext(input, bits) : (float)input;
    if(with_offset) value += offset;
    if(with_scale) value *= scale;

: (Sign extension) . SignExtend.

libiio

libiio-loop.c

.

#    uri
# uri = "ip:127.0.0.1"
# uri = "local:"
# uri = "usb:"
ctx = iio_create_context_from_uri(uri);

#  
#  device = icm20608
dev = iio_context_find_device(ctx, device);

#   
nb_channels = iio_device_get_channels_count(dev);

#   
for(int i = 0; i < nb_channels; i++)
    iio_channel_enable(iio_device_get_channel(dev, i));

# buffer_size = SAMPLES_PER_READ,    (  )
buffer = iio_device_create_buffer(dev, buffer_size, false);

#    
iio_buffer_set_blocking_mode(buffer, true);

while(true) {
    #  
    iio_buffer_refill(buffer);

    #   -      libiio
    #     "" ,        
    #    
    # ssize_t print_sample(const struct iio_channel *chn, void *buffer, size_t bytes, __notused void *d)
    # const struct iio_channel *chn -     
    # void *buffer -        
    # size_t bytes -    
    # __notused void *d -         iio_buffer_foreach_sample
    iio_buffer_foreach_sample(buffer, print_sample, NULL);
}

#  
iio_buffer_destroy(buffer);

#  
iio_context_destroy(ctx);