【AXIS】AXI-Stream FIFO设计实现（四）——异步时钟

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  前文介绍了几种同步时钟情况下的AXI Stream FIFO实现方式，一般来说，FIFO也需要承担异步时钟域模块间数据传输的功能，本文介绍异步AXIS FIFO的实现方式。

  如前文所说，AXI-Stream FIFO十分类似于FWFT异步FIFO，推荐参考前文FWFT异步FIFO的实现方式【FIFO】Standard / FWFT FIFO设计实现（二）——异步时钟，也可以参考同步AXIS FIFO的实现方式【AXIS】AXI-Stream FIFO设计实现（一）——基本模式。

  对于已经实现好的FWFT FIFO，只进行些许调整，将其写FIFO信号wr_en替换为s_axis_tvalid，将FIFO写满信号wfull替换为_{s_axis_tready，将读FIFO信号rd_en替换为m_axis_tvalid，将FIFO读空信号rempty替换为}m_axis_tready。

`timescale 1ns / 1psmodule async_axis_fifo_tb();localparam TDATA_WIDTH = 4;bit m_clk;bit s_clk;bit   [TDATA_WIDTH - 1 : 0]   m_axis_tdata;bit                           m_axis_tvalid; // wr_enbit                           m_axis_tready; // ~wfullbit   [TDATA_WIDTH - 1 : 0]   s_axis_tdata;  bit                           s_axis_tvalid; // ~remptybit                           s_axis_tready;always #5 m_clk = ~m_clk;always #7 s_clk = ~s_clk;logic [TDATA_WIDTH - 1 : 0] send_queue[$], recv_queue[$];always_ff @(posedge m_clk) beginif (~m_axis_tvalid) begin`ifdef FLOWm_axis_tvalid <= 1;`elsem_axis_tvalid <= $random();`endifm_axis_tdata <= $random();end else if (m_axis_tvalid & m_axis_tready) begin`ifdef FLOWm_axis_tvalid <= 1;`elsem_axis_tvalid <= $random();`endifm_axis_tdata <= $random();endendinitial begin forever beginif (m_axis_tvalid & m_axis_tready) beginsend_queue.push_back(m_axis_tdata);end@(posedge m_clk);endendinitial beginforever beginif (s_axis_tvalid & s_axis_tready) beginrecv_queue.push_back(s_axis_tdata);endif (send_queue.size != 0 && recv_queue.size != 0) beginif (send_queue[0] == recv_queue[0]) beginsend_queue.pop_front();recv_queue.pop_front();end else begin$error();$stop();endend@(posedge s_clk);endendalways_ff @(posedge s_clk) begin`ifdef FLOWs_axis_tready <= 1;`elses_axis_tready <= $random();`endifendlogic wfull, rempty;assign m_axis_tready = ~wfull;assign s_axis_tvalid = ~rempty;async_fifo_huge #(.TDATA_WIDTH    (TDATA_WIDTH    ),.FIFO_DEPTH     (4) // 2 ** n) async_fifo_huge_inst(.m_clk(m_clk),.s_clk(s_clk),.m_axis_tdata(m_axis_tdata),.wr_en(m_axis_tvalid), .wfull(wfull),.s_axis_tdata(s_axis_tdata),  .rempty(rempty), .rd_en(s_axis_tready));
endmodule

  下图展示了通过调整利用FWFT FIFO作为AXI Stream FIFO进行数据传输的仿真波形，其中上半部分为FWFT FIFO，下半部分为AXIS Stream输入激励。

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