AXI 协议中outstanding和burst的配合

在 AXI（Advanced eXtensible Interface）协议中，outstanding 和 burst 是两个关键术语，用于描述数据传输的特性。

Outstanding（未完成的）是指在数据传输期间，发送方还未收到接收方的确认信号。当一个传输请求被发出时，发送方会等待接收方返回确认信号，表示接收方已准备好接收数据。如果发送方在收到确认信号之前发送了另一个传输请求，那么第一个传输请求就称为“outstanding”。

Burst（突发）则是指在一个时钟周期内连续传输多个数据。AXI协议支持突发传输，这意味着在一次传输请求中可以连续传输多个数据项，而不需要每次传输都进行单独的请求和确认。

因此，在AXI协议中，outstanding 和 burst 配合使用，可以实现高效的数据传输。发送方可以连续发送多个数据项形成一个 burst，然后等待接收方的确认信号。如果在确认信号返回之前发送了另一个burst，那么第一个burst就是outstanding的。

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相关问题

AXI outstanding可以和burst一同生效吗

可以，AXI outstanding和burst可以同时生效。AXI (Advanced eXtensible Interface) 是一种高性能、高带宽、低功耗的总线协议，用于连接处理器、内存和外设等模块。AXI支持多种传输方式，包括burst传输。而AXI outstanding是指在一个burst传输中可以同时存在的未完成的事务数目。因此，在使用AXI协议进行burst传输时，可以通过设置AXI outstanding的值来控制同一时间内可以存在的未完成事务的数量。这样可以提高系统的吞吐量和性能。

verilog AXI slave with outstanding

An AXI slave with outstanding transactions can be implemented in Verilog by using a state machine to manage the response to incoming transactions. The state machine can keep track of the number of outstanding transactions and respond accordingly. Here is an example implementation:

module axi_slave_outstanding(
  input          aclk,
  input          aresetn,
  input          awvalid,
  input  [31:0]  awaddr,
  input  [2:0]   awprot,
  input          awcache,
  input          awburst,
  input  [3:0]   awlen,
  input          arvalid,
  input  [31:0]  araddr,
  input  [2:0]   arprot,
  input          arcache,
  input          arburst,
  input  [3:0]   arlen,
  input          wvalid,
  input  [31:0]  wdata,
  input  [3:0]   wstrb,
  input          wlast,
  output         bvalid,
  output         rvalid,
  output  [1:0]  rresp,
  output  [31:0] rdata,
  output         rlast
);

  reg [1:0] state;
  reg [31:0] mem[0:1023];
  reg [3:0] arcount;
  reg [3:0] awcount;
  
  // Reset state machine and counters on reset
  always @(posedge aclk) begin
    if (!aresetn) begin
      state <= 2'b00;
      arcount <= 4'b0000;
      awcount <= 4'b0000;
    end
  end
  
  // State machine
  always @(posedge aclk) begin
    case (state)
      // Idle state
      2'b00: begin
        if (awvalid) begin
          state <= 2'b01;
          awcount <= awlen;
        end else if (arvalid) begin
          state <= 2'b10;
          arcount <= arlen;
        end
      end
      // Write data state
      2'b01: begin
        if (wvalid) begin
          mem[awaddr] <= wdata;
          awaddr <= awaddr + 1;
          awcount <= awcount - 1;
          if (wlast) begin
            bvalid <= 1'b1;
            state <= 2'b00;
          end
        end
      end
      // Read data state
      2'b10: begin
        if (rcount == 4'b0000) begin
          rvalid <= 1'b1;
          rdata <= mem[araddr];
        end
        araddr <= araddr + 1;
        arcount <= arcount - 1;
        if (arcount == 4'b0000) begin
          rlast <= 1'b1;
          rvalid <= 1'b0;
          state <= 2'b00;
        end
      end
      // Error state
      default: begin
        state <= 2'b00;
      end
    endcase
  end
endmodule

In this implementation, the state machine has three states: idle, write data, and read data. When an AXI write transaction is received, the state machine transitions to the write data state and writes the incoming data to memory. It also keeps track of the number of outstanding write transactions using the `awcount` counter. When an AXI read transaction is received, the state machine transitions to the read data state and reads the requested data from memory. It also keeps track of the number of outstanding read transactions using the `arcount` counter.

The `bvalid`, `rvalid`, `rdata`, and `rlast` outputs are used to signal the completion of the AXI transactions to the master. The `bvalid` output is set to 1 when a write response is ready, and the `rvalid` output is set to 1 when a read response is ready. The `rdata` output contains the read data, and the `rlast` output signals the end of a read transaction.

This implementation assumes a single master and a single slave, and does not support burst transactions or interleaved transactions. It also does not support any AXI extensions beyond the basic read and write transactions.