-Old-Kits: Attaching an I2C Device to MicroE Click Connector

This application note describes how to connect an I2C device to the J1 MicroE Click Connector and enabled the device support in the Linux kernel. The DS1339 Real-Time Clock chip is used to demonstrate this capability.

Connect a DS1339 sensor to the J1 MicroE Click Connector as follows:
- J1B.9 - GND
- J1B.12 - SCL
- J1B.13 - SDA
- J1A.7 - VCC

Boot the board and check that an I2C device (0x68) is found on Bus I2C2:

/ # i2cdetect -y 2
     0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f
00:          -- -- -- -- -- -- -- -- -- -- -- -- --
10: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
20: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
30: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
40: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
50: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
60: -- -- -- -- -- -- -- -- 68 -- -- -- -- -- -- --
70: -- -- -- -- -- -- -- --

Check out the STM32MP1 kernel source code as described in Application Note Building Linux Kernel.

Add a device node description for the DS1339 sensor to the I2C2 node of the device tree (arch/arm/boot/dts/stm32mp157x-bsb.dtsi):

&i2c2 {                                                                                                                                                                                                    
        pinctrl-names = "default", "sleep";                                                                                                                                                                
        pinctrl-0 = <&i2c2_pins_a>;                                                                                                                                                                        
        pinctrl-1 = <&i2c2_sleep_pins_a>;                                                                                                                                                                  
        i2c-scl-rising-time-ns = <185>;                                                                                                                                                                    
        i2c-scl-falling-time-ns = <20>;                                                                                                                                                                    
        /delete-property/dmas;                                                                                                                                                                             
        /delete-property/dma-names;                                                                                                                                                                        
        status = "okay";                                                                                                                                                                                   
        clock-frequency = <1000000>;                                                                                                                                                                       

        ds1339: rtc@68 {                                                                                                                                                                                   
               compatible = "dallas,ds1339";                                                                                                                                                              
               reg = <0x68>;                                                                                                                                                                              
               trickle-resistor-ohms = <250>;                                                                                                                                                             
               trickle-diode-disable;                                                                                                                                                                     
        };                                                                                                                                                                                                           
};

Rebuild and update the kernel on the board.
The DS1339 Real-Time Clock chip should be visible as the /dev/rtc1 device in the system.