详解并掌握AXI4总线协议（四）、AXI4_FULL_SLAVE接口源码分析以及仿真验证

本文主要是介绍详解并掌握AXI4总线协议（四）、AXI4_FULL_SLAVE接口源码分析以及仿真验证，希望对大家解决编程问题提供一定的参考价值，需要的开发者们随着小编来一起学习吧！

系列文章目录

详解并掌握AXI4总线协议（一）、AXI4-FULL接口介绍
详解并掌握AXI4总线协议（二）、AXI4_FULL_MASTER接口源码分析以及仿真验证
详解并掌握AXI4总线协议（三）、基于AXI4_FULL接口的BRAM读写仿真验证

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一、前言

  在上前面几篇文章中，我们了解了AXI4协议的架构、传输机制以及各个信号的功能，以及AXI4_FULL_MASTERd在本文中，我们来研究Xilinx中AXI4_FULL_master接口是怎么实现、以及通过仿真来验证并且加深我们对AXI4协议的理解。

二、生成axi4_full_slave接口模板

  首先在Tools栏点击创建和打包新的IP

  然后点击创建AXI4接口

  然后自己命名

  然后选择FULL接口，Slave模式

  最后选择vip快速验证

三、分析axi4_full_slave接口代码

  我们先打开代码，然后逐步分析代码，整个代码如下：

`timescale 1 ns / 1 psmodule axi4_full_slave_v1_0_S_AXI #(// Users to add parameters here// User parameters ends// Do not modify the parameters beyond this line// Width of ID for for write address, write data, read address and read dataparameter integer C_S_AXI_ID_WIDTH	= 1,// Width of S_AXI data busparameter integer C_S_AXI_DATA_WIDTH	= 32,// Width of S_AXI address busparameter integer C_S_AXI_ADDR_WIDTH	= 6,// Width of optional user defined signal in write address channelparameter integer C_S_AXI_AWUSER_WIDTH	= 0,// Width of optional user defined signal in read address channelparameter integer C_S_AXI_ARUSER_WIDTH	= 0,// Width of optional user defined signal in write data channelparameter integer C_S_AXI_WUSER_WIDTH	= 0,// Width of optional user defined signal in read data channelparameter integer C_S_AXI_RUSER_WIDTH	= 0,// Width of optional user defined signal in write response channelparameter integer C_S_AXI_BUSER_WIDTH	= 0)(// Users to add ports here// User ports ends// Do not modify the ports beyond this line// Global Clock Signalinput wire  S_AXI_ACLK,// Global Reset Signal. This Signal is Active LOWinput wire  S_AXI_ARESETN,// Write Address IDinput wire [C_S_AXI_ID_WIDTH-1 : 0] S_AXI_AWID,// Write addressinput wire [C_S_AXI_ADDR_WIDTH-1 : 0] S_AXI_AWADDR,// Burst length. The burst length gives the exact number of transfers in a burstinput wire [7 : 0] S_AXI_AWLEN,// Burst size. This signal indicates the size of each transfer in the burstinput wire [2 : 0] S_AXI_AWSIZE,// Burst type. The burst type and the size information, // determine how the address for each transfer within the burst is calculated.input wire [1 : 0] S_AXI_AWBURST,// Lock type. Provides additional information about the// atomic characteristics of the transfer.input wire  S_AXI_AWLOCK,// Memory type. This signal indicates how transactions// are required to progress through a system.input wire [3 : 0] S_AXI_AWCACHE,// Protection type. This signal indicates the privilege// and security level of the transaction, and whether// the transaction is a data access or an instruction access.input wire [2 : 0] S_AXI_AWPROT,// Quality of Service, QoS identifier sent for each// write transaction.input wire [3 : 0] S_AXI_AWQOS,// Region identifier. Permits a single physical interface// on a slave to be used for multiple logical interfaces.input wire [3 : 0] S_AXI_AWREGION,// Optional User-defined signal in the write address channel.input wire [C_S_AXI_AWUSER_WIDTH-1 : 0] S_AXI_AWUSER,// Write address valid. This signal indicates that// the channel is signaling valid write address and// control information.input wire  S_AXI_AWVALID,// Write address ready. This signal indicates that// the slave is ready to accept an address and associated// control signals.output wire  S_AXI_AWREADY,// Write Datainput wire [C_S_AXI_DATA_WIDTH-1 : 0] S_AXI_WDATA,// Write strobes. This signal indicates which byte// lanes hold valid data. There is one write strobe// bit for each eight bits of the write data bus.input wire [(C_S_AXI_DATA_WIDTH/8)-1 : 0] S_AXI_WSTRB,// Write last. This signal indicates the last transfer// in a write burst.input wire  S_AXI_WLAST,// Optional User-defined signal in the write data channel.input wire [C_S_AXI_WUSER_WIDTH-1 : 0] S_AXI_WUSER,// Write valid. This signal indicates that valid write// data and strobes are available.input wire  S_AXI_WVALID,// Write ready. This signal indicates that the slave// can accept the write data.output wire  S_AXI_WREADY,// Response ID tag. This signal is the ID tag of the// write response.output wire [C_S_AXI_ID_WIDTH-1 : 0] S_AXI_BID,// Write response. This signal indicates the status// of the write transaction.output wire [1 : 0] S_AXI_BRESP,// Optional User-defined signal in the write response channel.output wire [C_S_AXI_BUSER_WIDTH-1 : 0] S_AXI_BUSER,// Write response valid. This signal indicates that the// channel is signaling a valid write response.output wire  S_AXI_BVALID,// Response ready. This signal indicates that the master// can accept a write response.input wire  S_AXI_BREADY,// Read address ID. This signal is the identification// tag for the read address group of signals.input wire [C_S_AXI_ID_WIDTH-1 : 0] S_AXI_ARID,// Read address. This signal indicates the initial// address of a read burst transaction.input wire [C_S_AXI_ADDR_WIDTH-1 : 0] S_AXI_ARADDR,// Burst length. The burst length gives the exact number of transfers in a burstinput wire [7 : 0] S_AXI_ARLEN,// Burst size. This signal indicates the size of each transfer in the burstinput wire [2 : 0] S_AXI_ARSIZE,// Burst type. The burst type and the size information, // determine how the address for each transfer within the burst is calculated.input wire [1 : 0] S_AXI_ARBURST,// Lock type. Provides additional information about the// atomic characteristics of the transfer.input wire  S_AXI_ARLOCK,// Memory type. This signal indicates how transactions// are required to progress through a system.input wire [3 : 0] S_AXI_ARCACHE,// Protection type. This signal indicates the privilege// and security level of the transaction, and whether// the transaction is a data access or an instruction access.input wire [2 : 0] S_AXI_ARPROT,// Quality of Service, QoS identifier sent for each// read transaction.input wire [3 : 0] S_AXI_ARQOS,// Region identifier. Permits a single physical interface// on a slave to be used for multiple logical interfaces.input wire [3 : 0] S_AXI_ARREGION,// Optional User-defined signal in the read address channel.input wire [C_S_AXI_ARUSER_WIDTH-1 : 0] S_AXI_ARUSER,// Write address valid. This signal indicates that// the channel is signaling valid read address and// control information.input wire  S_AXI_ARVALID,// Read address ready. This signal indicates that// the slave is ready to accept an address and associated// control signals.output wire  S_AXI_ARREADY,// Read ID tag. This signal is the identification tag// for the read data group of signals generated by the slave.output wire [C_S_AXI_ID_WIDTH-1 : 0] S_AXI_RID,// Read Dataoutput wire [C_S_AXI_DATA_WIDTH-1 : 0] S_AXI_RDATA,// Read response. This signal indicates the status of// the read transfer.output wire [1 : 0] S_AXI_RRESP,// Read last. This signal indicates the last transfer// in a read burst.output wire  S_AXI_RLAST,// Optional User-defined signal in the read address channel.output wire [C_S_AXI_RUSER_WIDTH-1 : 0] S_AXI_RUSER,// Read valid. This signal indicates that the channel// is signaling the required read data.output wire  S_AXI_RVALID,// Read ready. This signal indicates that the master can// accept the read data and response information.input wire  S_AXI_RREADY);// AXI4FULL signalsreg [C_S_AXI_ADDR_WIDTH-1 : 0] 	axi_awaddr;reg  	axi_awready;reg  	axi_wready;reg [1 : 0] 	axi_bresp;reg [C_S_AXI_BUSER_WIDTH-1 : 0] 	axi_buser;reg  	axi_bvalid;reg [C_S_AXI_ADDR_WIDTH-1 : 0] 	axi_araddr;reg  	axi_arready;reg [C_S_AXI_DATA_WIDTH-1 : 0] 	axi_rdata;reg [1 : 0] 	axi_rresp;reg  	axi_rlast;reg [C_S_AXI_RUSER_WIDTH-1 : 0] 	axi_ruser;reg  	axi_rvalid;// aw_wrap_en determines wrap boundary and enables wrappingwire aw_wrap_en;// ar_wrap_en determines wrap boundary and enables wrappingwire ar_wrap_en;// aw_wrap_size is the size of the write transfer, the// write address wraps to a lower address if upper address// limit is reachedwire [31:0]  aw_wrap_size ; // ar_wrap_size is the size of the read transfer, the// read address wraps to a lower address if upper address// limit is reachedwire [31:0]  ar_wrap_size ; // The axi_awv_awr_flag flag marks the presence of write address validreg axi_awv_awr_flag;//The axi_arv_arr_flag flag marks the presence of read address validreg axi_arv_arr_flag; // The axi_awlen_cntr internal write address counter to keep track of beats in a burst transactionreg [7:0] axi_awlen_cntr;//The axi_arlen_cntr internal read address counter to keep track of beats in a burst transactionreg [7:0] axi_arlen_cntr;reg [1:0] axi_arburst;reg [1:0] axi_awburst;reg [7:0] axi_arlen;reg [7:0] axi_awlen;//local parameter for addressing 32 bit / 64 bit C_S_AXI_DATA_WIDTH//ADDR_LSB is used for addressing 32/64 bit registers/memories//ADDR_LSB = 2 for 32 bits (n downto 2) //ADDR_LSB = 3 for 42 bits (n downto 3)localparam integer ADDR_LSB = (C_S_AXI_DATA_WIDTH/32)+ 1;localparam integer OPT_MEM_ADDR_BITS = 3;localparam integer USER_NUM_MEM = 1;//----------------------------------------------//-- Signals for user logic memory space example//------------------------------------------------wire [OPT_MEM_ADDR_BITS:0] mem_address;wire [USER_NUM_MEM-1:0] mem_select;reg [C_S_AXI_DATA_WIDTH-1:0] mem_data_out[0 : USER_NUM_MEM-1];genvar i;genvar j;genvar mem_byte_index;// I/O Connections assignmentsassign S_AXI_AWREADY	= axi_awready;assign S_AXI_WREADY	= axi_wready;assign S_AXI_BRESP	= axi_bresp;assign S_AXI_BUSER	= axi_buser;assign S_AXI_BVALID	= axi_bvalid;assign S_AXI_ARREADY	= axi_arready;assign S_AXI_RDATA	= axi_rdata;assign S_AXI_RRESP	= axi_rresp;assign S_AXI_RLAST	= axi_rlast;assign S_AXI_RUSER	= axi_ruser;assign S_AXI_RVALID	= axi_rvalid;assign S_AXI_BID = S_AXI_AWID;assign S_AXI_RID = S_AXI_ARID;assign  aw_wrap_size = (C_S_AXI_DATA_WIDTH/8 * (axi_awlen)); assign  ar_wrap_size = (C_S_AXI_DATA_WIDTH/8 * (axi_arlen)); assign  aw_wrap_en = ((axi_awaddr & aw_wrap_size) == aw_wrap_size)? 1'b1: 1'b0;assign  ar_wrap_en = ((axi_araddr & ar_wrap_size) == ar_wrap_size)? 1'b1: 1'b0;// Implement axi_awready generation// axi_awready is asserted for one S_AXI_ACLK clock cycle when both// S_AXI_AWVALID and S_AXI_WVALID are asserted. axi_awready is// de-asserted when reset is low.always @( posedge S_AXI_ACLK )beginif ( S_AXI_ARESETN == 1'b0 )beginaxi_awready <= 1'b0;axi_awv_awr_flag <= 1'b0;end elsebegin    if (~axi_awready && S_AXI_AWVALID && ~axi_awv_awr_flag && ~axi_arv_arr_flag)begin// slave is ready to accept an address and// associated control signalsaxi_awready <= 1'b1;axi_awv_awr_flag  <= 1'b1; // used for generation of bresp() and bvalidendelse if (S_AXI_WLAST && axi_wready)          // preparing to accept next address after current write burst tx completionbeginaxi_awv_awr_flag  <= 1'b0;endelse        beginaxi_awready <= 1'b0;endend end       // Implement axi_awaddr latching// This process is used to latch the address when both // S_AXI_AWVALID and S_AXI_WVALID are valid. always @( posedge S_AXI_ACLK )beginif ( S_AXI_ARESETN == 1'b0 )beginaxi_awaddr <= 0;axi_awlen_cntr <= 0;axi_awburst <= 0;axi_awlen <= 0;end elsebegin    if (~axi_awready && S_AXI_AWVALID && ~axi_awv_awr_flag)begin// address latching axi_awaddr <= S_AXI_AWADDR[C_S_AXI_ADDR_WIDTH - 1:0];  axi_awburst <= S_AXI_AWBURST; axi_awlen <= S_AXI_AWLEN;     // start address of transferaxi_awlen_cntr <= 0;end   else if((axi_awlen_cntr <= axi_awlen) && axi_wready && S_AXI_WVALID)        beginaxi_awlen_cntr <= axi_awlen_cntr + 1;case (axi_awburst)2'b00: // fixed burst// The write address for all the beats in the transaction are fixedbeginaxi_awaddr <= axi_awaddr;          //for awsize = 4 bytes (010)end   2'b01: //incremental burst// The write address for all the beats in the transaction are increments by awsizebeginaxi_awaddr[C_S_AXI_ADDR_WIDTH - 1:ADDR_LSB] <= axi_awaddr[C_S_AXI_ADDR_WIDTH - 1:ADDR_LSB] + 1;//awaddr aligned to 4 byte boundaryaxi_awaddr[ADDR_LSB-1:0]  <= {ADDR_LSB{1'b0}};   //for awsize = 4 bytes (010)end   2'b10: //Wrapping burst// The write address wraps when the address reaches wrap boundary if (aw_wrap_en)beginaxi_awaddr <= (axi_awaddr - aw_wrap_size); endelse beginaxi_awaddr[C_S_AXI_ADDR_WIDTH - 1:ADDR_LSB] <= axi_awaddr[C_S_AXI_ADDR_WIDTH - 1:ADDR_LSB] + 1;axi_awaddr[ADDR_LSB-1:0]  <= {ADDR_LSB{1'b0}}; end                      default: //reserved (incremental burst for example)beginaxi_awaddr <= axi_awaddr[C_S_AXI_ADDR_WIDTH - 1:ADDR_LSB] + 1;//for awsize = 4 bytes (010)endendcase              endend end       // Implement axi_wready generation// axi_wready is asserted for one S_AXI_ACLK clock cycle when both// S_AXI_AWVALID and S_AXI_WVALID are asserted. axi_wready is // de-asserted when reset is low. always @( posedge S_AXI_ACLK )beginif ( S_AXI_ARESETN == 1'b0 )beginaxi_wready <= 1'b0;end elsebegin    if ( ~axi_wready && S_AXI_WVALID && axi_awv_awr_flag)begin// slave can accept the write dataaxi_wready <= 1'b1;end//else if (~axi_awv_awr_flag)else if (S_AXI_WLAST && axi_wready)beginaxi_wready <= 1'b0;endend end       // Implement write response logic generation// The write response and response valid signals are asserted by the slave // when axi_wready, S_AXI_WVALID, axi_wready and S_AXI_WVALID are asserted.  // This marks the acceptance of address and indicates the status of // write transaction.always @( posedge S_AXI_ACLK )beginif ( S_AXI_ARESETN == 1'b0 )beginaxi_bvalid <= 0;axi_bresp <= 2'b0;axi_buser <= 0;end elsebegin    if (axi_awv_awr_flag && axi_wready && S_AXI_WVALID && ~axi_bvalid && S_AXI_WLAST )beginaxi_bvalid <= 1'b1;axi_bresp  <= 2'b0; // 'OKAY' response end                   elsebeginif (S_AXI_BREADY && axi_bvalid) //check if bready is asserted while bvalid is high) //(there is a possibility that bready is always asserted high)   beginaxi_bvalid <= 1'b0; end  endendend   // Implement axi_arready generation// axi_arready is asserted for one S_AXI_ACLK clock cycle when// S_AXI_ARVALID is asserted. axi_awready is // de-asserted when reset (active low) is asserted. // The read address is also latched when S_AXI_ARVALID is // asserted. axi_araddr is reset to zero on reset assertion.always @( posedge S_AXI_ACLK )beginif ( S_AXI_ARESETN == 1'b0 )beginaxi_arready <= 1'b0;axi_arv_arr_flag <= 1'b0;end elsebegin    if (~axi_arready && S_AXI_ARVALID && ~axi_awv_awr_flag && ~axi_arv_arr_flag)beginaxi_arready <= 1'b1;axi_arv_arr_flag <= 1'b1;endelse if (axi_rvalid && S_AXI_RREADY && axi_arlen_cntr == axi_arlen)// preparing to accept next address after current read completionbeginaxi_arv_arr_flag  <= 1'b0;endelse        beginaxi_arready <= 1'b0;endend end       // Implement axi_araddr latching//This process is used to latch the address when both //S_AXI_ARVALID and S_AXI_RVALID are valid. always @( posedge S_AXI_ACLK )beginif ( S_AXI_ARESETN == 1'b0 )beginaxi_araddr <= 0;axi_arlen_cntr <= 0;axi_arburst <= 0;axi_arlen <= 0;axi_rlast <= 1'b0;axi_ruser <= 0;end elsebegin    if (~axi_arready && S_AXI_ARVALID && ~axi_arv_arr_flag)begin// address latching axi_araddr <= S_AXI_ARADDR[C_S_AXI_ADDR_WIDTH - 1:0]; axi_arburst <= S_AXI_ARBURST; axi_arlen <= S_AXI_ARLEN;     // start address of transferaxi_arlen_cntr <= 0;axi_rlast <= 1'b0;end   else if((axi_arlen_cntr <= axi_arlen) && axi_rvalid && S_AXI_RREADY)        beginaxi_arlen_cntr <= axi_arlen_cntr + 1;axi_rlast <= 1'b0;case (axi_arburst)2'b00: // fixed burst// The read address for all the beats in the transaction are fixedbeginaxi_araddr       <= axi_araddr;        //for arsize = 4 bytes (010)end   2'b01: //incremental burst// The read address for all the beats in the transaction are increments by awsizebeginaxi_araddr[C_S_AXI_ADDR_WIDTH - 1:ADDR_LSB] <= axi_araddr[C_S_AXI_ADDR_WIDTH - 1:ADDR_LSB] + 1; //araddr aligned to 4 byte boundaryaxi_araddr[ADDR_LSB-1:0]  <= {ADDR_LSB{1'b0}};   //for awsize = 4 bytes (010)end   2'b10: //Wrapping burst// The read address wraps when the address reaches wrap boundary if (ar_wrap_en) beginaxi_araddr <= (axi_araddr - ar_wrap_size); endelse beginaxi_araddr[C_S_AXI_ADDR_WIDTH - 1:ADDR_LSB] <= axi_araddr[C_S_AXI_ADDR_WIDTH - 1:ADDR_LSB] + 1; //araddr aligned to 4 byte boundaryaxi_araddr[ADDR_LSB-1:0]  <= {ADDR_LSB{1'b0}};   end                      default: //reserved (incremental burst for example)beginaxi_araddr <= axi_araddr[C_S_AXI_ADDR_WIDTH - 1:ADDR_LSB]+1;//for arsize = 4 bytes (010)endendcase              endelse if((axi_arlen_cntr == axi_arlen) && ~axi_rlast && axi_arv_arr_flag )   beginaxi_rlast <= 1'b1;end          else if (S_AXI_RREADY)   beginaxi_rlast <= 1'b0;end          end end       // Implement axi_arvalid generation// axi_rvalid is asserted for one S_AXI_ACLK clock cycle when both // S_AXI_ARVALID and axi_arready are asserted. The slave registers // data are available on the axi_rdata bus at this instance. The // assertion of axi_rvalid marks the validity of read data on the // bus and axi_rresp indicates the status of read transaction.axi_rvalid // is deasserted on reset (active low). axi_rresp and axi_rdata are // cleared to zero on reset (active low).  always @( posedge S_AXI_ACLK )beginif ( S_AXI_ARESETN == 1'b0 )beginaxi_rvalid <= 0;axi_rresp  <= 0;end elsebegin    if (axi_arv_arr_flag && ~axi_rvalid)beginaxi_rvalid <= 1'b1;axi_rresp  <= 2'b0; // 'OKAY' responseend   else if (axi_rvalid && S_AXI_RREADY)beginaxi_rvalid <= 1'b0;end            endend    // ------------------------------------------// -- Example code to access user logic memory region// ------------------------------------------generateif (USER_NUM_MEM >= 1)beginassign mem_select  = 1;assign mem_address = (axi_arv_arr_flag? axi_araddr[ADDR_LSB+OPT_MEM_ADDR_BITS:ADDR_LSB]:(axi_awv_awr_flag? axi_awaddr[ADDR_LSB+OPT_MEM_ADDR_BITS:ADDR_LSB]:0));endendgenerate// implement Block RAM(s)generate for(i=0; i<= USER_NUM_MEM-1; i=i+1)begin:BRAM_GENwire mem_rden;wire mem_wren;assign mem_wren = axi_wready && S_AXI_WVALID ;assign mem_rden = axi_arv_arr_flag ; //& ~axi_rvalidfor(mem_byte_index=0; mem_byte_index<= (C_S_AXI_DATA_WIDTH/8-1); mem_byte_index=mem_byte_index+1)begin:BYTE_BRAM_GENwire [8-1:0] data_in ;wire [8-1:0] data_out;reg  [8-1:0] byte_ram [0 : 15];integer  j;//assigning 8 bit dataassign data_in  = S_AXI_WDATA[(mem_byte_index*8+7) -: 8];assign data_out = byte_ram[mem_address];always @( posedge S_AXI_ACLK )beginif (mem_wren && S_AXI_WSTRB[mem_byte_index])beginbyte_ram[mem_address] <= data_in;end   end    always @( posedge S_AXI_ACLK )beginif (mem_rden)beginmem_data_out[i][(mem_byte_index*8+7) -: 8] <= data_out;end   end    endend       endgenerate//Output register or memory read dataalways @( mem_data_out, axi_rvalid)beginif (axi_rvalid) begin// Read address muxaxi_rdata <= mem_data_out[0];end   elsebeginaxi_rdata <= 32'h00000000;end       end    // Add user logic here// User logic endsendmodule

3.1 输入输出接口信号分析

3.1.1 自定义参数

		parameter integer C_S_AXI_ID_WIDTH		= 1,	//读写ID的数据位宽parameter integer C_S_AXI_DATA_WIDTH	= 32,	//读写数据的位宽parameter integer C_S_AXI_ADDR_WIDTH	= 6,	//读写地址的位宽parameter integer C_S_AXI_AWUSER_WIDTH	= 0,	//用户自定义信号位宽，没使用就不管它parameter integer C_S_AXI_ARUSER_WIDTH	= 0,parameter integer C_S_AXI_WUSER_WIDTH	= 0,parameter integer C_S_AXI_RUSER_WIDTH	= 0,parameter integer C_S_AXI_BUSER_WIDTH	= 0

3.1.2 AXI4接口信号

		input wire  S_AXI_ACLK,								//全局时钟input wire  S_AXI_ARESETN,							//全局复位信号，低电平有效//写地址通道信号input 	wire [C_S_AXI_ID_WIDTH-1 : 0] S_AXI_AWID,		input 	wire [C_S_AXI_ADDR_WIDTH-1 : 0] S_AXI_AWADDR,input 	wire [7 : 0] S_AXI_AWLEN,input 	wire [2 : 0] S_AXI_AWSIZE,input 	wire [1 : 0] S_AXI_AWBURST,input 	wire  S_AXI_AWLOCK,input 	wire [3 : 0] S_AXI_AWCACHE,input 	wire [2 : 0] S_AXI_AWPROT,input 	wire [3 : 0] S_AXI_AWQOS,input 	wire [3 : 0] S_AXI_AWREGION,input 	wire [C_S_AXI_AWUSER_WIDTH-1 : 0] S_AXI_AWUSER,input 	wire  S_AXI_AWVALID,output 	wire  S_AXI_AWREADY,//写数据通道input 	wire [C_S_AXI_DATA_WIDTH-1 : 0] S_AXI_WDATA,input 	wire [(C_S_AXI_DATA_WIDTH/8)-1 : 0] S_AXI_WSTRB,input 	wire  S_AXI_WLAST,input 	wire [C_S_AXI_WUSER_WIDTH-1 : 0] S_AXI_WUSER,input 	wire  S_AXI_WVALID,output 	wire  S_AXI_WREADY,//写响应通道output 	wire [C_S_AXI_ID_WIDTH-1 : 0] S_AXI_BID,output 	wire [1 : 0] S_AXI_BRESP,output 	wire [C_S_AXI_BUSER_WIDTH-1 : 0] S_AXI_BUSER,output 	wire  S_AXI_BVALID,input 	wire  S_AXI_BREADY,//读地址通道input 	wire [C_S_AXI_ID_WIDTH-1 : 0] S_AXI_ARID,input 	wire [C_S_AXI_ADDR_WIDTH-1 : 0] S_AXI_ARADDR,input 	wire [7 : 0] S_AXI_ARLEN,input 	wire [2 : 0] S_AXI_ARSIZE,input 	wire [1 : 0] S_AXI_ARBURST,input 	wire  S_AXI_ARLOCK,input 	wire [3 : 0] S_AXI_ARCACHE,input 	wire [2 : 0] S_AXI_ARPROT,input 	wire [3 : 0] S_AXI_ARQOS,input 	wire [3 : 0] S_AXI_ARREGION,input 	wire [C_S_AXI_ARUSER_WIDTH-1 : 0] S_AXI_ARUSER,input 	wire  S_AXI_ARVALID,output 	wire  S_AXI_ARREADY,//读数据通道output 	wire [C_S_AXI_ID_WIDTH-1 : 0] S_AXI_RID,output 	wire [C_S_AXI_DATA_WIDTH-1 : 0] S_AXI_RDATA,output 	wire [1 : 0] S_AXI_RRESP,output 	wire  S_AXI_RLAST,output 	wire [C_S_AXI_RUSER_WIDTH-1 : 0] S_AXI_RUSER,output 	wire  S_AXI_RVALID,input 	wire  S_AXI_RREADY

  AXI4的信号已在上一文章中详细介绍，这里就不再赘述。

3.2 局部参数定义

	reg             [C_S_AXI_ADDR_WIDTH-1 : 0]          axi_awaddr  ;		//写地址reg                                                 axi_awready ;		//写地址准备信号reg                                                 axi_wready  ;		//写数据准备信号reg             [1 : 0]                             axi_bresp   ;		//写响应reg             [C_S_AXI_BUSER_WIDTH-1 : 0]         axi_buser   ;		//写响应用户自定义信号reg                                                 axi_bvalid  ;		//写响应valid信号reg             [C_S_AXI_ADDR_WIDTH-1 : 0]          axi_araddr  ;		//读地址信号reg                                                 axi_arready ;		//读地址准备信号reg             [C_S_AXI_DATA_WIDTH-1 : 0]          axi_rdata   ;		//读数据reg             [1 : 0]                             axi_rresp   ;		//读响应信号reg                                                 axi_rlast   ;		//读突发最后一个数据信号reg             [C_S_AXI_RUSER_WIDTH-1 : 0]         axi_ruser   ;		//读通道用户自定义信号reg                                                 axi_rvalid  ;		//读valid信号

	wire                                                aw_wrap_en  ;		//写突发类型中的包模式，确定包装边界并启用包wire                                                ar_wrap_en  ;		//读突发类型中的包模式，确定包装边界并启用包wire            [31:0]                              aw_wrap_size ;		//写传输的大小，如果达到地址上限，则写地址将回到最低的地址wire            [31:0]                              ar_wrap_size ; 		//读传输的大小，如果达到地址上限，则读地址将回到最低的地址reg                                                 axi_awv_awr_flag ;	//整个写操作标志信号reg                                                 axi_arv_arr_flag ; 	//整个读操作标志信号reg             [7:0]                               axi_awlen_cntr  ;	//一次突发中，写数据个数计数器reg             [7:0]                               axi_arlen_cntr  ;	//一次突发中，读数据个数计数器reg             [1:0]                               axi_arburst ;		//读突发类型reg             [1:0]                               axi_awburst ;		//写突发类型reg             [7:0]                               axi_arlen   ;		//读突发长度reg             [7:0]                               axi_awlen   ;		//写突发长度

	localparam  integer                                 ADDR_LSB    = (C_S_AXI_DATA_WIDTH/32)+ 1;//地址的最低变化位，AXI中，一个字节占用一个地址，一个写数据32位占用4个字节。因此写一次数据，地址+4localparam  integer                                 OPT_MEM_ADDR_BITS   = 3;				//存储器地址位宽localparam  integer                                 USER_NUM_MEM    = 1;					//存储器地址的数量wire            [OPT_MEM_ADDR_BITS:0]               mem_address ;							//存储器地址wire            [USER_NUM_MEM-1:0]                  mem_select  ;							//选择寄存器信号reg             [C_S_AXI_DATA_WIDTH-1:0]            mem_data_out    [0 : USER_NUM_MEM-1];	//定义一个32位宽的寄存器数组

3.3 写地址通道代码分析

  从前面几篇文章我们知道，AXI一共有五个传输通道，每个通道都有对应的握手信号，因此要想AXI传输成功，就必须重点实现握手信号的时序。

always @( posedge S_AXI_ACLK )beginif ( S_AXI_ARESETN == 1'b0 )beginaxi_awready <= 1'b0;axi_awv_awr_flag <= 1'b0;end elsebegin    if (~axi_awready && S_AXI_AWVALID && ~axi_awv_awr_flag && ~axi_arv_arr_flag)		//当主机发出valid信号，并且当前没有读和没有写的时候，拉高aw_ready信号beginaxi_awready <= 1'b1;axi_awv_awr_flag  <= 1'b1; endelse if (S_AXI_WLAST && axi_wready)   //当写完最后一个数据后，拉低axi_awv_awr_flag表示一次突发写完成   					beginaxi_awv_awr_flag  <= 1'b0;endelse        beginaxi_awready <= 1'b0;endend endalways @( posedge S_AXI_ACLK )beginif ( S_AXI_ARESETN == 1'b0 )beginaxi_awaddr <= 0;axi_awlen_cntr <= 0;axi_awburst <= 0;axi_awlen <= 0;end elsebegin    if (~axi_awready && S_AXI_AWVALID && ~axi_awv_awr_flag)				//当前没有写操作时，aw信号握手成功后，将主机发送的写地址信号以及写突发类型，写突发长度暂存下来begin// address latching axi_awaddr <= S_AXI_AWADDR[C_S_AXI_ADDR_WIDTH - 1:0];  axi_awburst <= S_AXI_AWBURST; axi_awlen <= S_AXI_AWLEN;     // start address of transferaxi_awlen_cntr <= 0;end   else if((axi_awlen_cntr <= axi_awlen) && axi_wready && S_AXI_WVALID)  //每当写数据握手成功一次， axi_awlen_cntr累加一次，直到达到一次写突发长度     beginaxi_awlen_cntr <= axi_awlen_cntr + 1;case (axi_awburst)												//根据突发类型来更改写入存储器里写地址2'b00: 															//固定地址突发模式，地址一直固定不变beginaxi_awaddr <= axi_awaddr;          end   2'b01: 															//增量模式突发beginaxi_awaddr[C_S_AXI_ADDR_WIDTH - 1:ADDR_LSB] <= axi_awaddr[C_S_AXI_ADDR_WIDTH - 1:ADDR_LSB] + 1;	//写数据握手成功，从地址第三位开始累加1axi_awaddr[ADDR_LSB-1:0]  <= {ADDR_LSB{1'b0}};   												//低两位不变，所以相当于每写一次地址+4end   2'b10: 															//包类型突发，类似于回环if (aw_wrap_en)begin														//当地址到包边界时，地址重新回到最低位axi_awaddr <= (axi_awaddr - aw_wrap_size); 				endelse beginaxi_awaddr[C_S_AXI_ADDR_WIDTH - 1:ADDR_LSB] <= axi_awaddr[C_S_AXI_ADDR_WIDTH - 1:ADDR_LSB] + 1;axi_awaddr[ADDR_LSB-1:0]  <= {ADDR_LSB{1'b0}}; end                      default: beginaxi_awaddr <= axi_awaddr[C_S_AXI_ADDR_WIDTH - 1:ADDR_LSB] + 1;endendcase              endend end       

3.4 写数据通道代码分析

always @( posedge S_AXI_ACLK )beginif ( S_AXI_ARESETN == 1'b0 )beginaxi_wready <= 1'b0;end elsebegin    if ( ~axi_wready && S_AXI_WVALID && axi_awv_awr_flag)	//当前在wr_flag信号写，主机发出valid信号时候，拉高wready信号beginaxi_wready <= 1'b1;endelse if (S_AXI_WLAST && axi_wready)					//写完最后一个数据后，拉低wready信号beginaxi_wready <= 1'b0;endend end

3.5 写响应通道代码分析

always @( posedge S_AXI_ACLK )beginif ( S_AXI_ARESETN == 1'b0 )beginaxi_bvalid <= 0;axi_bresp <= 2'b0;axi_buser <= 0;end elsebegin    if (axi_awv_awr_flag && axi_wready && S_AXI_WVALID && ~axi_bvalid && S_AXI_WLAST ) //当写完最后一个数据后 拉高bvalid信号以及回复OKAYbeginaxi_bvalid <= 1'b1;axi_bresp  <= 2'b0; end                   elsebeginif (S_AXI_BREADY && axi_bvalid) 								//握手成功后拉低beginaxi_bvalid <= 1'b0; end  endendend 

3.6 读地址通道代码分析

always @( posedge S_AXI_ACLK )beginif ( S_AXI_ARESETN == 1'b0 )beginaxi_arready <= 1'b0;axi_arv_arr_flag <= 1'b0;end elsebegin    if (~axi_arready && S_AXI_ARVALID && ~axi_awv_awr_flag && ~axi_arv_arr_flag)	//当前没有在写和读时候，当主机发出arvalid信号时，拉高arready信号beginaxi_arready <= 1'b1;axi_arv_arr_flag <= 1'b1;													//并且拉高rdflag信号endelse if (axi_rvalid && S_AXI_RREADY && axi_arlen_cntr == axi_arlen)			//当最后一个数据读出并且握手成功后，拉低rdflag信号beginaxi_arv_arr_flag  <= 1'b0;endelse        beginaxi_arready <= 1'b0;endend endalways @( posedge S_AXI_ACLK )beginif ( S_AXI_ARESETN == 1'b0 )beginaxi_araddr <= 0;axi_arlen_cntr <= 0;axi_arburst <= 0;axi_arlen <= 0;axi_rlast <= 1'b0;axi_ruser <= 0;end elsebegin    if (~axi_arready && S_AXI_ARVALID && ~axi_arv_arr_flag)			//当地址通道信号握手成功后,将读地址信号,读突发类型,读突发长度信号暂存下来beginaxi_araddr <= S_AXI_ARADDR[C_S_AXI_ADDR_WIDTH - 1:0]; 		axi_arburst <= S_AXI_ARBURST; axi_arlen <= S_AXI_ARLEN;     axi_arlen_cntr <= 0;axi_rlast <= 1'b0;end   else if((axi_arlen_cntr <= axi_arlen) && axi_rvalid && S_AXI_RREADY) //每次读数据握手成功后，读数据数量计数器累加一       beginaxi_arlen_cntr <= axi_arlen_cntr + 1;axi_rlast <= 1'b0;case (axi_arburst)					//根据突发类型选择地址，跟上面写通道一致2'b00: beginaxi_araddr       <= axi_araddr;        end   2'b01:beginaxi_araddr[C_S_AXI_ADDR_WIDTH - 1:ADDR_LSB] <= axi_araddr[C_S_AXI_ADDR_WIDTH - 1:ADDR_LSB] + 1; axi_araddr[ADDR_LSB-1:0]  <= {ADDR_LSB{1'b0}};   end   2'b10: if (ar_wrap_en) beginaxi_araddr <= (axi_araddr - ar_wrap_size); endelse beginaxi_araddr[C_S_AXI_ADDR_WIDTH - 1:ADDR_LSB] <= axi_araddr[C_S_AXI_ADDR_WIDTH - 1:ADDR_LSB] + 1; axi_araddr[ADDR_LSB-1:0]  <= {ADDR_LSB{1'b0}};   end                      default: beginaxi_araddr <= axi_araddr[C_S_AXI_ADDR_WIDTH - 1:ADDR_LSB]+1;endendcase              endelse if((axi_arlen_cntr == axi_arlen) && ~axi_rlast && axi_arv_arr_flag )   //当准备发送最后一个读数据时，拉高rlast信号beginaxi_rlast <= 1'b1;end          else if (S_AXI_RREADY)   //握手成功后拉低beginaxi_rlast <= 1'b0;end          end end

3.7 读数据通道代码分析

always @( posedge S_AXI_ACLK )beginif ( S_AXI_ARESETN == 1'b0 )beginaxi_rvalid <= 0;axi_rresp  <= 0;end elsebegin    if (axi_arv_arr_flag && ~axi_rvalid)beginaxi_rvalid <= 1'b1;		//当读标志有效时，拉高rvalidaxi_rresp  <= 2'b0; 		//回复 okend   else if (axi_rvalid && S_AXI_RREADY)beginaxi_rvalid <= 1'b0;end            endend //定义存储器+
generateif (USER_NUM_MEM >= 1)beginassign mem_select  = 1;assign mem_address = (axi_arv_arr_flag? axi_araddr[ADDR_LSB+OPT_MEM_ADDR_BITS:ADDR_LSB]:(axi_awv_awr_flag? axi_awaddr[ADDR_LSB+OPT_MEM_ADDR_BITS:ADDR_LSB]:0));endendgenerate// implement Block RAM(s)generate for(i=0; i<= USER_NUM_MEM-1; i=i+1)begin:BRAM_GENwire mem_rden;wire mem_wren;assign mem_wren = axi_wready && S_AXI_WVALID ;assign mem_rden = axi_arv_arr_flag ; //& ~axi_rvalidfor(mem_byte_index=0; mem_byte_index<= (C_S_AXI_DATA_WIDTH/8-1); mem_byte_index=mem_byte_index+1)begin:BYTE_BRAM_GENwire [8-1:0] data_in ;wire [8-1:0] data_out;reg  [8-1:0] byte_ram [0 : 15];integer  j;//assigning 8 bit dataassign data_in  = S_AXI_WDATA[(mem_byte_index*8+7) -: 8];assign data_out = byte_ram[mem_address];always @( posedge S_AXI_ACLK )beginif (mem_wren && S_AXI_WSTRB[mem_byte_index])beginbyte_ram[mem_address] <= data_in;end   end    always @( posedge S_AXI_ACLK )beginif (mem_rden)beginmem_data_out[i][(mem_byte_index*8+7) -: 8] <= data_out;end   end    endend       endgeneratealways @( mem_data_out, axi_rvalid)beginif (axi_rvalid) begin// Read address muxaxi_rdata <= mem_data_out[0];end   elsebeginaxi_rdata <= 32'h00000000;end       end 

四、仿真结果

  因为本次验证，直接添加的VIP快速验证，因此直接开始跑仿真即可，将不同通道信号用不同颜色区分开来，仿真如下：

4.1 观察写通道仿真

1. 首先等待写地址通道握手成功后，写起始地址从0开始，突发类型为增量突发，突发长度为8
2. 然后等待写地址通道握手成功后，写数据通道给出写数据以及valid信号，每次握手成功，写数据累加1，然后与从机握手7次后，最后一次数据伴随着wlast，等待握手
3. 当一次写突发完成后，等待从机回复信号握手成功

  整个仿真结果与手册给出的通道示意图一致：

4.2 观察读通道仿真

  当主机给出读地址信号以及arvalid信号，与从机握手成功后，从机根据突发大小以及突发类型给出读数据，此时给出的读数据是从1-8，与前面写入的数据一致。

  整个读通道的时序图和AXI协议给出的整体框图一致：

  因此整个AXI4_FULL_SLAVE接口的读写仿真验证已经完成。

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