Neza-D1开发板学习之I2C-OLED篇

1. Neza-D1开发板扩展IO上引出了I2C2，从原理图上看，已经接了PCF8574@38了，总线速度400K,我们的OLED也是接在这上边的,由于这屏幕比较小，显示不了多少东西，就不用FB方式了，直接在应用层操作OLED，所以设备树也不需要配置

2. 在应用层操作就跟单片机操作是一样的了，这里为了方便操作屏幕，我分辨率移植u8g2这个库，我手里的哦了的是1.3”的，驱动IC是SHT1106，用1306也可以，只能显示不满屏，可能是基地址定义的不一样

3. 我们不需要从OLED读取数据，所以只需要实现I2C写函数就可以，注意OLED模块上标的地址是0x78，这个是8位地址，这里使用的是7位地址，右移一位所以是0x3C

    unsigned char i2c_init()
    {
        const char *i2c_dev = "/dev/i2c-2";
        fd = open(i2c_dev, O_RDWR);
        if (fd < 0)
        {
            printf("not have /dev/i2c-2 t\r\n");
            fflush(stdout);
            return -1;
        }
        return 0;
    }
    // I2C Addr 7bit
    unsigned char base_i2c_write(unsigned char device_addr, unsigned char *buff, int num)
    {
   
        struct i2c_rdwr_ioctl_data data;
        struct i2c_msg msgs_str[1];
        data.msgs = msgs_str;
        data.nmsgs = 1;
        data.msgs[0].len = num;
        data.msgs[0].addr = device_addr;
        data.msgs[0].flags = 0;
        data.msgs[0].buf = buff;
        ioctl(fd, I2C_RDWR, (unsigned long)&data);
    }
   

4. 移植u8g2 非常简单，只需修改这下边这个函数里初始化位置和写数据位置就行，另外一个是延时，可以不用修改
   uint8_t u8x8_byte_hw_i2c(u8x8_t *u8x8, uint8_t msg, uint8_t arg_int, void arg_ptr)
   {
   / u8g2/u8x8 will never send more than 32 bytes between START_TRANSFER and END_TRANSFER */
   static uint8_t buffer[128];
   static uint8_t buf_idx;
   uint8_t data;
   
   switch (msg)
   {
   case U8X8_MSG_BYTE_INIT:
   {
   / add your custom code to init i2c subsystem */
   i2c_init; // I2C初始化
   }
   break;
   
   case U8X8_MSG_BYTE_START_TRANSFER:
   {
   buf_idx = 0;
   }
   break;
   
   case U8X8_MSG_BYTE_SEND:
   {
   data = (uint8_t *)arg_ptr;
   
   while (arg_int > 0)
   {
   buffer[buf_idx++] = *data;
   data++;
   arg_int–;
   }
   }
   break;
   
   case U8X8_MSG_BYTE_END_TRANSFER:
   {
   //i2c写函数
   if (base_i2c_write(OLED_ADDRESS, buffer, buf_idx) != 0)
   return 0;
   }
   break;
   
   case U8X8_MSG_BYTE_SET_DC:
   break;
   
   default:
   return 0;
   }
   
   return 1;
   }
   
   uint8_t u8x8_gpio_and_delay(u8x8_t *u8x8, uint8_t msg, uint8_t arg_int, void arg_ptr)
   {
   switch (msg)
   {
   case U8X8_MSG_DELAY_100NANO: // delay arg_int * 100 nano seconds
   break;
   case U8X8_MSG_DELAY_10MICRO: // delay arg_int * 10 micro seconds
   break;
   case U8X8_MSG_DELAY_MILLI: // delay arg_int * 1 milli second
   break;
   case U8X8_MSG_DELAY_I2C: // arg_int is the I2C speed in 100KHz, e.g. 4 = 400 KHz
   break; // arg_int=1: delay by 5us, arg_int = 4: delay by 1.25us
   case U8X8_MSG_GPIO_I2C_CLOCK: // arg_int=0: Output low at I2C clock pin
   break; // arg_int=1: Input dir with pullup high for I2C clock pin
   case U8X8_MSG_GPIO_I2C_DATA: // arg_int=0: Output low at I2C data pin
   break; // arg_int=1: Input dir with pullup high for I2C data pin
   case U8X8_MSG_GPIO_MENU_SELECT:
   u8x8_SetGPIOResult(u8x8, / get menu select pin state / 0);
   break;
   case U8X8_MSG_GPIO_MENU_NEXT:
   u8x8_SetGPIOResult(u8x8, / get menu next pin state / 0);
   break;
   case U8X8_MSG_GPIO_MENU_PREV:
   u8x8_SetGPIOResult(u8x8, / get menu prev pin state / 0);
   break;
   case U8X8_MSG_GPIO_MENU_HOME:
   u8x8_SetGPIOResult(u8x8, / get menu home pin state */ 0);
   break;
   default:
   u8x8_SetGPIOResult(u8x8, 1); // default return value
   break;
   }
   return 1;
   }

5. 这就移植完了，下边编译一下传到开发板里，可以看到显示成功

6. 最后附上完整工程