实现CAN总线通讯的自测试功能，如果硬件条件具备，也可用来实现CAN控制器之间的通讯。 具体内容见代码中每一句的注释，经调试成功-CAN bus communication realize the self-test function, if hardware conditions are ripe, but also can be used to realize communication between the CAN controller. The specific content o