高速接口中多指针弹性缓冲器设计

Design of multiple pointer elastic buffer for high-speed interface

弹性缓冲器广泛应用于高速接口物理层,一般通过读写指针跳跃和断点保存来完成跳跃字符(SKP)的添加和删除.高速接口对于这种单指针读写的弹性缓冲器有很高的频率要求,容易产生复杂的时序问题.为此基于FPGA,以USB3.0协议为标准,设计了一个具有4个读写指针寻址来实现SKP添加和删除的弹性缓冲器.首先利用输入控制单元改变输入数据中SKP对的排序,输出控制单元改变输出的数据;其次在阈值检测单元中检测弹性缓冲器中的有效数据量是否达到添加或删除的阈值,发出有效指令到读写指针控制单元;最后通过控制4个读写指针寻址来添加和删除数据中的SKP,维持弹性缓冲器的半满状态.实验结果表明,设计的弹性缓冲器可正确实现SKP的添加和删除功能,且时钟频率能够满足USB3.0的协议要求.

Elastic buffers are widely used in the high speed interface of the physical layer,which usually completes the addition and deletion of skip（SKP）by reading/writing pointer jumping and breakpoint preservation.However,common single pointer elastic buffer must be operated at high frequencies,which would make it easy to create complex timing problems.To solve these problems,based on the FPGA and the USB3.0 protocol,a four read/write pointer addressing elastic buffer to complete the addition and deletion of SKP has been proposed.First,the elastic buffer makes use of the input control unit to change the sequence of the SKP pairs in the input data and the output control unit to change the output data.Then,the threshold detection unit sends the valid instructions to the read/write pointer control unit by checking whether the amount of valid data in the elastic buffer achieves the threshold which is added or deleted.Last,to maintain the elastic buffer in half full state,the SKP in data is added or deleted by controlling the addressing of the four read/write pointers.Experimental results show that the designedelastic buffer can achieve the function of SKP addition and deletion,and its clock frequency can satisfy the protocol of Universal Serial Bus 3.0.