Inter Integrated Circuit

I²C (Inter-Integrated Circuit), pronounced I-squared-C, is a multi-master, multi-slave, single-ended, serial computer bus invented by Philips Semiconductor (now NXP Semiconductors). It is typically used for attaching lower-speed peripheral ICs to processors and microcontrollers. Wikipedia

• Linux Journal Greg Kroah-Hartman I2C Drivers Part I

• Linux Journal Greg Kroah-Hartman I2C Drivers Part II

Required Hardware

One I2C sensor

Kernel Integration

Kernel Display Message

    root@edison:~# dmesg | grep -i i2c
    [    0.190675] I2C bus = 1, name =      pcal9555a-1, irq = 0x 0, addr = 0x20
    [    0.190711] I2C bus = 1, name =      pcal9555a-2, irq = 0x 0, addr = 0x21
    [    0.190743] I2C bus = 1, name =      pcal9555a-3, irq = 0x 0, addr = 0x22
    [    0.190774] I2C bus = 1, name =      pcal9555a-4, irq = 0x 0, addr = 0x23
    [    0.746686] i2c /dev entries driver

Userspace Interfaces

SysFs

    root@edison:~# ls /sys/class/i2c-dev/
    i2c-1  i2c-2  i2c-3  i2c-4  i2c-5  i2c-6  i2c-7

DevFs

    root@edison:~# ls /dev/i2c-*
    /dev/i2c-1  /dev/i2c-2  /dev/i2c-3  /dev/i2c-4  /dev/i2c-5  /dev/i2c-6  /dev/i2c-7

ProcFs

    root@edison:~# cat /proc/interrupts | grep i2c
      7:         44          0   IO-APIC-fasteoi   i2c-    designware-1
     10:          0          0   IO-APIC-fasteoi   i2c-designware-2
     12:          0          0   IO-APIC-fasteoi   watchdog, i2c-designware-3
     13:          0          0   IO-APIC-fasteoi   i2c-designware-4
     14:          0          0   IO-APIC-fasteoi   i2c-designware-5
     15:          0          0   IO-APIC-fasteoi   i2c-designware-6
     16:          0          0   IO-APIC-fasteoi   i2c-designware-7

Applications / Libraries

Setup

Opkg

    root@edison:~# opkg install i2c-tools
    Package i2c-tools (3.1.1-r0) installed in root is up to date.
    ...

Programs

i2cdetect

    root@edison:~# i2cdetect -y -r 1
         0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f
    00:          -- -- -- -- -- -- -- -- -- -- -- -- -- 
    10: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 
    20: UU UU UU UU -- -- -- -- -- -- -- -- -- -- -- -- 
    30: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 
    40: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 
    50: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 
    60: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 
    70: -- -- -- -- -- -- -- --