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.