Rk3399 development board i2c4 attaching EEPROM instance

Feiling embedded OK3399-C The development board is reserved I2C4 Pin interface , be located P32 Pin on pin , Namely I2C4_SCL and I2C4_SDA. Through this article, the editor will list and explain how to use I2C4 mount at24c08（EEPROM） chip .

Modify the result

1、 modify kernel/arch/arm64/boot/dts/rockchip/OK3399.dts, Add and modify as follows ：

2、 Enucleation at24c08 Pull up resistance on the module , Use of flying wire 1.8V Power the module , Access I2C4_SCL and I2C4_SDA.

Change your mind

We're going to add a I2C The idea of the equipment is ： Add a description to the device tree -> Add the corresponding device driver in the device tree description -> Add device drivers to the kernel .

According to the idea , First, in the device tree I2C4 Add under node at24c08 Device information for . stay kernel/arch/arm64/boot/dts/rockchip/OK3399-C.dts file , find I2C4 The nodes are as follows ：

At present, it is disabled The state of , And there is no device information . Add device information as follows ：

Pictured above , Tell the kernel through the device tree ,I2C4 Start using , And a EEPROM equipment , Name is [email protected], The driver used is compatible=“”;

Now we lack this driver , General I2C The driver file used by the device corresponds to I2C The manufacturer will provide , If the manufacturer says there is no need to drive , It doesn't really mean “ Unwanted ” drive , Instead, their devices can use universal drivers .

This is the equipment in this article , After communicating with the manufacturer, he said that there was no driver file . Then search directly under the kernel directory eeprom、at24 Such words , Find out if there is a corresponding general driver file .

It can be seen that kernel/drivers/misc/eeprom/at24.c file .

See how the content matches the use of this driver , Normally, the driver file should be reserved .compatible= *** Call the interface of the driver as a device tree , As long as it is in the device tree description compatible And In the driver file .compatible As described in , It will match successfully .

But this at24.c Not in China .compatible, only one at24_ids Among them ”24c08”：

Compare at25.c The document has .compatible No, ids.

ids And .compatible equally , The device tree is used to identify matching , Among the three recognition matching conditions, those who are interested can go deep . Because it has nothing to do with this article , I won't repeat . So I found the corresponding driver file , Return to the device tree and add a description .

Now this tells the kernel that I want to use I2C4, my I2C4 There's a next one. EEPROM equipment , It uses “24c08” drive , But not yet ”24c08” This file is sent to the kernel , Then the next goal is to program the driver into the kernel .

stay kernel Run in directory makemenuconfig, Search for at24, as follows ：

Press the number 1, Automatically jump to the corresponding option , Press down y Choose , Save and exit .

because makemenuconfig The change is .config file , The compiled script will be regenerated every time .config file , So in order for the modification to take effect , Modify the compilation script , Make it not regenerate .config file , as follows ：

Will generate .config Comment out the command of the file , Compiling the kernel , This will be ”24c08” To the kernel , Also tell the kernel through the device tree ,I2C4 There's a next one. EEPROM The equipment should use “24c08”.

Here we are , Our routine idea of adding devices has been completed ： Add a description to the device tree -> The device tree describes the corresponding device driver -> Add device drivers to the kernel .

The next step is to compile the kernel , burning boot Mirror to the development board , Use i2ctool Command to view , I won't repeat it here i2ctool How to use the command . Use command ：i2cdetect-l 、i2cdetect-y 4.

The corresponding address has been registered by the driver , But not generated devices Under the I2C4 equipment , It indicates that the module may not work properly , View module related information .

The module comes with I2C4 Pull up resistance , because OK3399-C The bottom plate also has a pull-up resistor, as shown in the figure below , And is 1.8V Pull up , For level matching , Without modifying the bottom plate , Use 1.8V Benchmarking , Remove the pull-up resistor attached to the module , Use 1.8V To configure .

Modify the device tree again , Add the clock description and device address description .

After compiling , Burning the kernel , After burning, start the development board .

Identify to I2C4 Under the equipment , Then conduct a read-write test , Following commands ：

echo"hello my world" > /sys/bus/i2c/devices/1-0050/eeprom

cat/sys/bus/i2c/devices/4-0050/eeprom

So far a new I2C EEPROM Device added successfully , Yes I2C The device can also be read and written through the i2ctool Related command operation .