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CAN FD的一种协议缺陷
资料介绍
在CAN演变为CANFD时,为了兼容性的考虑,仅对头部作了少量修改,然后设置了一个数据域位速率的选择位BRS,如果选CANFD,那么BRS位之后就切换为高速传送,这种简单的处理疏忽了初始相位差的影响。当后发送节点胜出时,先发节点的领先相位差需要在后面的重同步中逐渐抵消,但是当BRS位前的重同步次数不够时,BRS位处的相位差甚至可以大于1个高速位,从而使接收节点高速位起始位置出错,导致传送出错。这是系统完全符合CANFD标准要求下的出错,属于一种协议缺陷。鉴于CANFD被认为是新一代的骨干通信协议,这一缺陷是不能容忍的,所以必须寻求解决方案。一种可能的解决方案是在仲裁域采用硬同步,但是电磁干扰中的毛刺可能使情况变得更糟。目前,没有找到理想的改进方案。
In the evolution from CAN to CAN FD,the most important consideration is downward compatibility.The head part of frame has small change,and then a bit BRS is defined as bit rate change flag.If the application chooses CAN FD,then after BRS the protocol engine using high bit rate for the following bits.This simplified treatment does not consider the big initial phase difference between transmitting nodes.When the later transmitting node won the arbitration,this initial phase needs more resynchronization to diminish.If there is less resynchronization,the phase difference at BRS is bigger than a fast bit.This leads the start position of fast bits in corresponding receiver wrong.And causes transmission fail.This failure occurs under normal protocol working condition.Hence it is a design flaw.Because CAN FD is considered as mainstay of automotive application,this failure is not tolerable.New fixing solution must be found.One possible method is using hard synchronization rule in arbitration field.But the glitch could make things even worse.This problem is still no solution.
部分文件列表
| 文件名 | 大小 |
| CAN_FD的一种协议缺陷.pdf | 1M |
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