## 编写设备驱动之i2c_client
参考资料：
* Linux内核文档:
* `Documentation\i2c\instantiating-devices.rst`
* `Documentation\i2c\writing-clients.rst`
* Linux内核驱动程序示例:
* `drivers/eeprom/at24.c`
* 本节代码：GIT仓库中
* `IMX6ULL\source\04_I2C\03_ap3216c_ok`
* `STM32MP157\source\A7\04_I2C\03_ap3216c_ok`
### 1. I2C总线-设备-驱动模型
### 2. 编译i2c_driver
* 增加Makefile
* 设置工具链
* IMX6ULL
```shell
export ARCH=arm
export CROSS_COMPILE=arm-linux-gnueabihf-
export PATH=$PATH:/home/book/100ask_imx6ull-sdk/ToolChain/gcc-linaro-6.2.1-2016.11-x86_64_arm-linux-gnueabihf/bin
```
* STM32MP157
```shell
source /home/book/100ask_stm32mp157_pro-sdk/ToolChain/openstlinux_eglfs-linux-gnueabi/environment-setup-cortexa7t2hf-neon-vfpv4-ostl-linux-gnueabi
export ARCH=arm
export CROSS_COMPILE=arm-ostl-linux-gnueabi-
```
* 编译
### 3. 编写测试程序
* 编程
* 设置工具链
* IMX6ULL
```shell
export ARCH=arm
export CROSS_COMPILE=arm-linux-gnueabihf-
export PATH=$PATH:/home/book/100ask_imx6ull-sdk/ToolChain/gcc-linaro-6.2.1-2016.11-x86_64_arm-linux-gnueabihf/bin
```
* STM32MP157
**注意**：对于STM32MP157，编译内核/驱动、编译APP的工具链不一样
```shell
export ARCH=arm
export CROSS_COMPILE=arm-buildroot-linux-gnueabihf-
export PATH=$PATH:/home/book/100ask_stm32mp157_pro-sdk/ToolChain/arm-buildroot-linux-gnueabihf_sdk-buildroot/bin
```
* 编译
```shell
// imx6ull
arm-linux-gnueabihf-gcc -o ap321
