STM32F7_I2C_RXDR
val = readb_relaxed(i2c_dev->base + STM32F7_I2C_RXDR);
STM32F7_I2C_RXDR);
*f7_msg->buf++ = readb_relaxed(base + STM32F7_I2C_RXDR);
readb_relaxed(base + STM32F7_I2C_RXDR);