本文转载自：孤独的单刀的CSDN博客
写在前面
接slave接口篇，本文继续打包一个AXI4-Full-Master接口的IP，学习下源码，再仿真看看波形。
1、调用IP
首先新建一个工程，然后点击Tools-----create and package new ip
点击Next
选择选项4，点击Next，各选项含义：
1---将当前工程打包为IP核
2----将当前工程的模块设计打包为IP核
3----将一个特定的文件夹目录打包为IP核
4----创建一个带AXI接口的IP核
填写IP信息（基本不修改，只改下名称方便后续管理），点击Next
选择Full接口，接口类型选择从机master，数据位宽32位，然后点击Next
这里选择第3个，使用AXI4 VIP来验证IP，然后点击Next。（AXI4 VIP是XILINX的一个IP核，该IP核可以提供多种连接方式来对AXI接口进行验证，用起来很是贴心方便，后面会写相关文章介绍，还请期待。）
到此就生成了一个master接口的验证工程。不着急仿真，先跟它耍耍。整个工程的结构如下：
双击上个表示的BD模块，打开工程框图，如下：
整个工程由两部分构成：1、我们打包的IP，该IP的接口是AIX4-Full-master；2、AXI Verification IP，这是一个AXI的验证IP，提供多种验证方式，功能很强大，双击这个IP，看看它的内置定制信息：
可以看到，它可选择接口模式来实现主机或从机或直通功能；可选协议类型，地址位宽，数据位宽等。我们这里不动它，直接cancel。
2、Master接口的源码分析
在如下路径下有生成的接口源码：
接下来双击打开，我们一探究竟。（由于源码较长900行，一次性展开不利于阅读，我接下来分块进行讲解）
NO.1----模块参数、输入输出信号：
参数主要是数据、地址、ID的位宽；目标从机的基地址。
接口即为标准的AXI4-Full的标准接口，忘记了信号定义的可以看这里：带你快速入门AXI4总线--AXI4-Full篇（1）----AXI4-Full总线
此外还有功能接口：1、INIT_AXI_TXN：开始发送事务信号；2、TXN_DONE：事务完成信号；3、ERROR：错误信号。
`timescale 1 ns / 1 ps module myip_axi4_Full_master_v1_0_M00_AXI # ( // Users to add parameters here // User parameters ends // Do not modify the parameters beyond this line // Base address of targeted slave parameter C_M_TARGET_SLAVE_BASE_ADDR = 32'h40000000, // Burst Length. Supports 1, 2, 4, 8, 16, 32, 64, 128, 256 burst lengths parameter integer C_M_AXI_BURST_LEN = 16, // Thread ID Width parameter integer C_M_AXI_ID_WIDTH = 1, // Width of Address Bus parameter integer C_M_AXI_ADDR_WIDTH = 32, // Width of Data Bus parameter integer C_M_AXI_DATA_WIDTH = 32, // Width of User Write Address Bus parameter integer C_M_AXI_AWUSER_WIDTH = 0, // Width of User Read Address Bus parameter integer C_M_AXI_ARUSER_WIDTH = 0, // Width of User Write Data Bus parameter integer C_M_AXI_WUSER_WIDTH = 0, // Width of User Read Data Bus parameter integer C_M_AXI_RUSER_WIDTH = 0, // Width of User Response Bus parameter integer C_M_AXI_BUSER_WIDTH = 0 ) ( // Users to add ports here // User ports ends // Do not modify the ports beyond this line // Initiate AXI transactions input wire INIT_AXI_TXN, // Asserts when transaction is complete output wire TXN_DONE, // Asserts when ERROR is detected output reg ERROR, // Global Clock Signal. input wire M_AXI_ACLK, // Global Reset Singal. This Signal is Active Low input wire M_AXI_ARESETN, // Master Interface Write Address ID output wire [C_M_AXI_ID_WIDTH-1 : 0] M_AXI_AWID, // Master Interface Write Address output wire [C_M_AXI_ADDR_WIDTH-1 : 0] M_AXI_AWADDR, // Burst length. The burst length gives the exact number of transfers in a burst output wire [7 : 0] M_AXI_AWLEN, // Burst size. This signal indicates the size of each transfer in the burst output wire [2 : 0] M_AXI_AWSIZE, // Burst type. The burst type and the size information, // determine how the address for each transfer within the burst is calculated. output wire [1 : 0] M_AXI_AWBURST, // Lock type. Provides additional information about the // atomic characteristics of the transfer. output wire M_AXI_AWLOCK, // Memory type. This signal indicates how transactions // are required to progress through a system. output wire [3 : 0] M_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. output wire [2 : 0] M_AXI_AWPROT, // Quality of Service, QoS identifier sent for each write transaction. output wire [3 : 0] M_AXI_AWQOS, // Optional User-defined signal in the write address channel. output wire [C_M_AXI_AWUSER_WIDTH-1 : 0] M_AXI_AWUSER, // Write address valid. This signal indicates that // the channel is signaling valid write address and control information. output wire M_AXI_AWVALID, // Write address ready. This signal indicates that // the slave is ready to accept an address and associated control signals input wire M_AXI_AWREADY, // Master Interface Write Data. output wire [C_M_AXI_DATA_WIDTH-1 : 0] M_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. output wire [C_M_AXI_DATA_WIDTH/8-1 : 0] M_AXI_WSTRB, // Write last. This signal indicates the last transfer in a write burst. output wire M_AXI_WLAST, // Optional User-defined signal in the write data channel. output wire [C_M_AXI_WUSER_WIDTH-1 : 0] M_AXI_WUSER, // Write valid. This signal indicates that valid write // data and strobes are available output wire M_AXI_WVALID, // Write ready. This signal indicates that the slave // can accept the write data. input wire M_AXI_WREADY, // Master Interface Write Response. input wire [C_M_AXI_ID_WIDTH-1 : 0] M_AXI_BID, // Write response. This signal indicates the status of the write transaction. input wire [1 : 0] M_AXI_BRESP, // Optional User-defined signal in the write response channel input wire [C_M_AXI_BUSER_WIDTH-1 : 0] M_AXI_BUSER, // Write response valid. This signal indicates that the // channel is signaling a valid write response. input wire M_AXI_BVALID, // Response ready. This signal indicates that the master // can accept a write response. output wire M_AXI_BREADY, // Master Interface Read Address. output wire [C_M_AXI_ID_WIDTH-1 : 0] M_AXI_ARID, // Read address. This signal indicates the initial // address of a read burst transaction. output wire [C_M_AXI_ADDR_WIDTH-1 : 0] M_AXI_ARADDR, // Burst length. The burst length gives the exact number of transfers in a burst output wire [7 : 0] M_AXI_ARLEN, // Burst size. This signal indicates the size of each transfer in the burst output wire [2 : 0] M_AXI_ARSIZE, // Burst type. The burst type and the size information, // determine how the address for each transfer within the burst is calculated. output wire [1 : 0] M_AXI_ARBURST, // Lock type. Provides additional information about the // atomic characteristics of the transfer. output wire M_AXI_ARLOCK, // Memory type. This signal indicates how transactions // are required to progress through a system. output wire [3 : 0] M_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. output wire [2 : 0] M_AXI_ARPROT, // Quality of Service, QoS identifier sent for each read transaction output wire [3 : 0] M_AXI_ARQOS, // Optional User-defined signal in the read address channel. output wire [C_M_AXI_ARUSER_WIDTH-1 : 0] M_AXI_ARUSER, // Write address valid. This signal indicates that // the channel is signaling valid read address and control information output wire M_AXI_ARVALID, // Read address ready. This signal indicates that // the slave is ready to accept an address and associated control signals input wire M_AXI_ARREADY, // Read ID tag. This signal is the identification tag // for the read data group of signals generated by the slave. input wire [C_M_AXI_ID_WIDTH-1 : 0] M_AXI_RID, // Master Read Data input wire [C_M_AXI_DATA_WIDTH-1 : 0] M_AXI_RDATA, // Read response. This signal indicates the status of the read transfer input wire [1 : 0] M_AXI_RRESP, // Read last. This signal indicates the last transfer in a read burst input wire M_AXI_RLAST, // Optional User-defined signal in the read address channel. input wire [C_M_AXI_RUSER_WIDTH-1 : 0] M_AXI_RUSER, // Read valid. This signal indicates that the channel // is signaling the required read data. input wire M_AXI_RVALID, // Read ready. This signal indicates that the master can // accept the read data and response information. output wire M_AXI_RREADY );
NO.2----函数、寄存器定义：
主要是对AXI4的输出端口的寄存器定义，避免直接对输出端口操作；
clogb2这个function实现的功能：以2为底取对数，主要是用来计算位宽。
状态机的状态定义：初始状态、发送状态、接收状态、比较（检查错误）状态。
// function called clogb2 that returns an integer which has the //value of the ceiling of the log base 2 // function called clogb2 that returns an integer which has the // value of the ceiling of the log base 2. function integer clogb2 (input integer bit_depth); begin for(clogb2=0; bit_depth>0; clogb2=clogb2+1) bit_depth = bit_depth >> 1; end endfunction // C_TRANSACTIONS_NUM is the width of the index counter for // number of write or read transaction. localparam integer C_TRANSACTIONS_NUM = clogb2(C_M_AXI_BURST_LEN-1); // Burst length for transactions, in C_M_AXI_DATA_WIDTHs. // Non-2^n lengths will eventually cause bursts across 4K address boundaries. localparam integer C_MASTER_LENGTH = 12; // total number of burst transfers is master length divided by burst length and burst size localparam integer C_NO_BURSTS_REQ = C_MASTER_LENGTH-clogb2((C_M_AXI_BURST_LEN*C_M_AXI_DATA_WIDTH/8)-1); // Example State machine to initialize counter, initialize write transactions, // initialize read transactions and comparison of read data with the // written data words. parameter [1:0] IDLE = 2'b00, // This state initiates AXI4Lite transaction // after the state machine changes state to INIT_WRITE // when there is 0 to 1 transition on INIT_AXI_TXN INIT_WRITE = 2'b01, // This state initializes write transaction, // once writes are done, the state machine // changes state to INIT_READ INIT_READ = 2'b10, // This state initializes read transaction // once reads are done, the state machine // changes state to INIT_COMPARE INIT_COMPARE = 2'b11; // This state issues the status of comparison // of the written data with the read data reg [1:0] mst_exec_state; // AXI4LITE signals //AXI4 internal temp signals reg [C_M_AXI_ADDR_WIDTH-1 : 0] axi_awaddr; reg axi_awvalid; reg [C_M_AXI_DATA_WIDTH-1 : 0] axi_wdata; reg axi_wlast; reg axi_wvalid; reg axi_bready; reg [C_M_AXI_ADDR_WIDTH-1 : 0] axi_araddr; reg axi_arvalid; reg axi_rready; //write beat count in a burst reg [C_TRANSACTIONS_NUM : 0] write_index; //read beat count in a burst reg [C_TRANSACTIONS_NUM : 0] read_index; //size of C_M_AXI_BURST_LEN length burst in bytes wire [C_TRANSACTIONS_NUM+2 : 0] burst_size_bytes; //The burst counters are used to track the number of burst transfers of C_M_AXI_BURST_LEN burst length needed to transfer 2^C_MASTER_LENGTH bytes of data. reg [C_NO_BURSTS_REQ : 0] write_burst_counter; reg [C_NO_BURSTS_REQ : 0] read_burst_counter; reg start_single_burst_write; reg start_single_burst_read; reg writes_done; reg reads_done; reg error_reg; reg compare_done; reg read_mismatch; reg burst_write_active; reg burst_read_active; reg [C_M_AXI_DATA_WIDTH-1 : 0] expected_rdata; //Interface response error flags wire write_resp_error; wire read_resp_error; wire wnext; wire rnext; reg init_txn_ff; reg init_txn_ff2; reg init_txn_edge; wire init_txn_pulse;
NO.3----wire信号赋值：
对AXI4的输出信号赋值，避免直接对其进行操作。
// I/O Connections assignments
//I/O Connections. Write Address (AW)
assign M_AXI_AWID = 'b0;
//The AXI address is a concatenation of the target base address + active offset range
assign M_AXI_AWADDR = C_M_TARGET_SLAVE_BASE_ADDR + axi_awaddr;
//Burst LENgth is number of transaction beats, minus 1
assign M_AXI_AWLEN = C_M_AXI_BURST_LEN - 1;
//Size should be C_M_AXI_DATA_WIDTH, in 2^SIZE bytes, otherwise narrow bursts are used
assign M_AXI_AWSIZE = clogb2((C_M_AXI_DATA_WIDTH/8)-1);
//INCR burst type is usually used, except for keyhole bursts
assign M_AXI_AWBURST = 2'b01;
assign M_AXI_AWLOCK = 1'b0;
//Update value to 4'b0011 if coherent accesses to be used via the Zynq ACP port. Not Allocated, Modifiable, not Bufferable. Not Bufferable since this example is meant to test memory, not intermediate cache.
assign M_AXI_AWCACHE = 4'b0010;
assign M_AXI_AWPROT = 3'h0;
assign M_AXI_AWQOS = 4'h0;
assign M_AXI_AWUSER = 'b1;
assign M_AXI_AWVALID = axi_awvalid;
//Write Data(W)
assign M_AXI_WDATA = axi_wdata;
//All bursts are complete and aligned in this example
assign M_AXI_WSTRB = {(C_M_AXI_DATA_WIDTH/8){1'b1}};
assign M_AXI_WLAST = axi_wlast;
assign M_AXI_WUSER = 'b0;
assign M_AXI_WVALID = axi_wvalid;
//Write Response (B)
assign M_AXI_BREADY = axi_bready;
//Read Address (AR)
assign M_AXI_ARID = 'b0;
assign M_AXI_ARADDR = C_M_TARGET_SLAVE_BASE_ADDR + axi_araddr;
//Burst LENgth is number of transaction beats, minus 1
assign M_AXI_ARLEN = C_M_AXI_BURST_LEN - 1;
//Size should be C_M_AXI_DATA_WIDTH, in 2^n bytes, otherwise narrow bursts are used
assign M_AXI_ARSIZE = clogb2((C_M_AXI_DATA_WIDTH/8)-1);
//INCR burst type is usually used, except for keyhole bursts
assign M_AXI_ARBURST = 2'b01;
assign M_AXI_ARLOCK = 1'b0;
//Update value to 4'b0011 if coherent accesses to be used via the Zynq ACP port. Not Allocated, Modifiable, not Bufferable. Not Bufferable since this example is meant to test memory, not intermediate cache.
assign M_AXI_ARCACHE = 4'b0010;
assign M_AXI_ARPROT = 3'h0;
assign M_AXI_ARQOS = 4'h0;
assign M_AXI_ARUSER = 'b1;
assign M_AXI_ARVALID = axi_arvalid;
//Read and Read Response (R)
assign M_AXI_RREADY = axi_rready;
//Example design I/O
assign TXN_DONE = compare_done;
//Burst size in bytes
assign burst_size_bytes = C_M_AXI_BURST_LEN * C_M_AXI_DATA_WIDTH/8;NO.4----捕获写事务开始信号的上升沿：
写事务开始信号INIT_AXI_TXN打拍，并捕获其上升沿，作为开始发送的标志信号。
assign init_txn_pulse = (!init_txn_ff2) && init_txn_ff; //Generate a pulse to initiate AXI transaction. always @(posedge M_AXI_ACLK) begin // Initiates AXI transaction delay if (M_AXI_ARESETN == 0 ) begin init_txn_ff <= 1'b0; init_txn_ff2 <= 1'b0; end else begin init_txn_ff <= INIT_AXI_TXN; init_txn_ff2 <= init_txn_ff; end end
NO.5----写地址通道：
写地址准备信号axi_awvalid：当单次突发写信号start_single_burst_write有效时，将其拉高。
写地址通道握手成功时同时对首地址axi_awaddr赋值。
always @(posedge M_AXI_ACLK) begin if (M_AXI_ARESETN == 0 || init_txn_pulse == 1'b1 ) begin axi_awvalid <= 1'b0; end // If previously not valid , start next transaction else if (~axi_awvalid && start_single_burst_write) begin axi_awvalid <= 1'b1; end /* Once asserted, VALIDs cannot be deasserted, so axi_awvalid must wait until transaction is accepted */ else if (M_AXI_AWREADY && axi_awvalid) begin axi_awvalid <= 1'b0; end else axi_awvalid <= axi_awvalid; end // Next address after AWREADY indicates previous address acceptance always @(posedge M_AXI_ACLK) begin if (M_AXI_ARESETN == 0 || init_txn_pulse == 1'b1) begin axi_awaddr <= 'b0; end else if (M_AXI_AWREADY && axi_awvalid) begin axi_awaddr <= axi_awaddr + burst_size_bytes; end else axi_awaddr <= axi_awaddr;
NO.6----写数据通道：
写数据准备信号axi_wvalid：当单次突发写信号start_single_burst_write有效时，将其拉高。
写入最后一个数据时拉高axi_wlast。
每写入一个数据，突发写入长度计数器write_index累加1.
在写入数据期间axi_wdata从0累加1.
assign wnext = M_AXI_WREADY & axi_wvalid; //写数据持续期间 // WVALID logic, similar to the axi_awvalid always block above always @(posedge M_AXI_ACLK) begin if (M_AXI_ARESETN == 0 || init_txn_pulse == 1'b1 ) begin axi_wvalid <= 1'b0; end // If previously not valid, start next transaction else if (~axi_wvalid && start_single_burst_write) begin axi_wvalid <= 1'b1; end /* If WREADY and too many writes, throttle WVALID Once asserted, VALIDs cannot be deasserted, so WVALID must wait until burst is complete with WLAST */ else if (wnext && axi_wlast) axi_wvalid <= 1'b0; else axi_wvalid <= axi_wvalid; end //WLAST generation on the MSB of a counter underflow // WVALID logic, similar to the axi_awvalid always block above always @(posedge M_AXI_ACLK) begin if (M_AXI_ARESETN == 0 || init_txn_pulse == 1'b1 ) begin axi_wlast <= 1'b0; end // axi_wlast is asserted when the write index // count reaches the penultimate count to synchronize // with the last write data when write_index is b1111 // else if (&(write_index[C_TRANSACTIONS_NUM-1:1])&& ~write_index[0] && wnext) else if (((write_index == C_M_AXI_BURST_LEN-2 && C_M_AXI_BURST_LEN >= 2) && wnext) || (C_M_AXI_BURST_LEN == 1 )) begin axi_wlast <= 1'b1; end // Deassrt axi_wlast when the last write data has been // accepted by the slave with a valid response else if (wnext) axi_wlast <= 1'b0; else if (axi_wlast && C_M_AXI_BURST_LEN == 1) axi_wlast <= 1'b0; else axi_wlast <= axi_wlast; end /* Burst length counter. Uses extra counter register bit to indicate terminal count to reduce decode logic */ always @(posedge M_AXI_ACLK) begin if (M_AXI_ARESETN == 0 || init_txn_pulse == 1'b1 || start_single_burst_write == 1'b1) begin write_index <= 0; end else if (wnext && (write_index != C_M_AXI_BURST_LEN-1)) begin write_index <= write_index + 1; end else write_index <= write_index; end /* Write Data Generator Data pattern is only a simple incrementing count from 0 for each burst */ always @(posedge M_AXI_ACLK) begin if (M_AXI_ARESETN == 0 || init_txn_pulse == 1'b1) axi_wdata <= 'b1; //else if (wnext && axi_wlast) // axi_wdata <= 'b0; else if (wnext) axi_wdata <= axi_wdata + 1; else axi_wdata <= axi_wdata; end
NO.7----写响应通道：
写响应准备信号axi_bready：当从机发送的M_AXI_BVALID有效时，将其拉高。
写响应错误信号write_resp_error：当接收的写响应有误时，将其拉高。
always @(posedge M_AXI_ACLK) begin if (M_AXI_ARESETN == 0 || init_txn_pulse == 1'b1 ) begin axi_bready <= 1'b0; end // accept/acknowledge bresp with axi_bready by the master // when M_AXI_BVALID is asserted by slave else if (M_AXI_BVALID && ~axi_bready) begin axi_bready <= 1'b1; end // deassert after one clock cycle else if (axi_bready) begin axi_bready <= 1'b0; end // retain the previous value else axi_bready <= axi_bready; end //Flag any write response errors assign write_resp_error = axi_bready & M_AXI_BVALID & M_AXI_BRESP[1];
NO.8----读地址通道：
读地址准备信号axi_arvalid：当单次突发读信号start_single_burst_read有效时，将其拉高。
读地址通道握手成功时同时对首地址axi_araddr赋值。
always @(posedge M_AXI_ACLK) begin if (M_AXI_ARESETN == 0 || init_txn_pulse == 1'b1 ) begin axi_arvalid <= 1'b0; end // If previously not valid , start next transaction else if (~axi_arvalid && start_single_burst_read) begin axi_arvalid <= 1'b1; end else if (M_AXI_ARREADY && axi_arvalid) begin axi_arvalid <= 1'b0; end else axi_arvalid <= axi_arvalid; end // Next address after ARREADY indicates previous address acceptance always @(posedge M_AXI_ACLK) begin if (M_AXI_ARESETN == 0 || init_txn_pulse == 1'b1) begin axi_araddr <= 'b0; end else if (M_AXI_ARREADY && axi_arvalid) begin axi_araddr <= axi_araddr + burst_size_bytes; end else axi_araddr <= axi_araddr; end
NO.9----读数据通道：
读数据准备信号axi_rready：当完成最后一个数据的读取后拉低，当从机发送的读有效信号M_AXI_RVALID有效时将其拉高。
每读取一个数据，突发读取长度计数器read_index累加1。
读不匹配信号read_mismatch：当读取数据与预期读取数据（写入的数据）不一致时，将其拉高。
读响应错误信号read_resp_error：一旦读取响应值非法就将其拉高。
预期读取数据expected_rdata：预期读到的数据，即写入数据。
错误信号error_reg：一旦满足以下三种错误即拉高：1、写响应错误；2、读响应错误；3、读、写内容不匹配。
// Forward movement occurs when the channel is valid and ready assign rnext = M_AXI_RVALID && axi_rready; //读数据期间 // Burst length counter. Uses extra counter register bit to indicate // terminal count to reduce decode logic always @(posedge M_AXI_ACLK) begin if (M_AXI_ARESETN == 0 || init_txn_pulse == 1'b1 || start_single_burst_read) begin read_index <= 0; end else if (rnext && (read_index != C_M_AXI_BURST_LEN-1)) begin read_index <= read_index + 1; end else read_index <= read_index; end /* The Read Data channel returns the results of the read request In this example the data checker is always able to accept more data, so no need to throttle the RREADY signal */ always @(posedge M_AXI_ACLK) begin if (M_AXI_ARESETN == 0 || init_txn_pulse == 1'b1 ) begin axi_rready <= 1'b0; end // accept/acknowledge rdata/rresp with axi_rready by the master // when M_AXI_RVALID is asserted by slave else if (M_AXI_RVALID) begin if (M_AXI_RLAST && axi_rready) begin axi_rready <= 1'b0; end else begin axi_rready <= 1'b1; end end // retain the previous value end //Check received read data against data generator always @(posedge M_AXI_ACLK) begin if (M_AXI_ARESETN == 0 || init_txn_pulse == 1'b1) begin read_mismatch <= 1'b0; end //Only check data when RVALID is active else if (rnext && (M_AXI_RDATA != expected_rdata)) begin read_mismatch <= 1'b1; end else read_mismatch <= 1'b0; end //Flag any read response errors assign read_resp_error = axi_rready & M_AXI_RVALID & M_AXI_RRESP[1]; //---------------------------------------- //Example design read check data generator //----------------------------------------- //Generate expected read data to check against actual read data always @(posedge M_AXI_ACLK) begin if (M_AXI_ARESETN == 0 || init_txn_pulse == 1'b1)// || M_AXI_RLAST) expected_rdata <= 'b1; else if (M_AXI_RVALID && axi_rready) expected_rdata <= expected_rdata + 1; else expected_rdata <= expected_rdata; end //---------------------------------- //Example design error register //---------------------------------- //Register and hold any data mismatches, or read/write interface errors always @(posedge M_AXI_ACLK) begin if (M_AXI_ARESETN == 0 || init_txn_pulse == 1'b1) begin error_reg <= 1'b0; end else if (read_mismatch || write_resp_error || read_resp_error) begin error_reg <= 1'b1; end else error_reg <= error_reg; end
NO.10----读、写突发长度计数：
读、写突发长度计数信号read_burst_counter、write_burst_counter在读写期间统计读、写的个数。
// write_burst_counter counter keeps track with the number of burst transaction initiated // against the number of burst transactions the master needs to initiate always @(posedge M_AXI_ACLK) begin if (M_AXI_ARESETN == 0 || init_txn_pulse == 1'b1 ) begin write_burst_counter <= 'b0; end else if (M_AXI_AWREADY && axi_awvalid) begin if (write_burst_counter[C_NO_BURSTS_REQ] == 1'b0) begin write_burst_counter <= write_burst_counter + 1'b1; //write_burst_counter[C_NO_BURSTS_REQ] <= 1'b1; end end else write_burst_counter <= write_burst_counter; end // read_burst_counter counter keeps track with the number of burst transaction initiated // against the number of burst transactions the master needs to initiate always @(posedge M_AXI_ACLK) begin if (M_AXI_ARESETN == 0 || init_txn_pulse == 1'b1) begin read_burst_counter <= 'b0; end else if (M_AXI_ARREADY && axi_arvalid) begin if (read_burst_counter[C_NO_BURSTS_REQ] == 1'b0) begin read_burst_counter <= read_burst_counter + 1'b1; //read_burst_counter[C_NO_BURSTS_REQ] <= 1'b1; end end else read_burst_counter <= read_burst_counter; end
NO.11----流程控制状态机：
该状态机有4个状态：
IDLE：初始状态，一旦写事务开始信号init_txn_pulse有效，即进入写事务状态INIT_WRITE
INIT_WRITE：写事务状态，在此状态完成64次长度为16的突发写事务。一旦所有写事务完成，即进入读事务状态INIT_READ
INIT_READ：读事务状态，在此状态完成64次长度为16的突发读事务。一旦所有读事务完成，即进入比较状态INIT_COMPARE
INIT_COMPARE：比较状态（比较错误），判断是否存在错误情况（读写不匹配、写响应错误或读响应错误），然后跳转回初始状态IDLE
//implement master command interface state machine always @ ( posedge M_AXI_ACLK) begin if (M_AXI_ARESETN == 1'b0 ) begin // reset condition // All the signals are assigned default values under reset condition mst_exec_state <= IDLE; start_single_burst_write <= 1'b0; start_single_burst_read <= 1'b0; compare_done <= 1'b0; ERROR <= 1'b0; end else begin // state transition case (mst_exec_state) IDLE: // This state is responsible to wait for user defined C_M_START_COUNT // number of clock cycles. if ( init_txn_pulse == 1'b1) begin mst_exec_state <= INIT_WRITE; ERROR <= 1'b0; compare_done <= 1'b0; end else begin mst_exec_state <= IDLE; end INIT_WRITE: // This state is responsible to issue start_single_write pulse to // initiate a write transaction. Write transactions will be // issued until burst_write_active signal is asserted. // write controller if (writes_done) begin mst_exec_state <= INIT_READ;// end else begin mst_exec_state <= INIT_WRITE; if (~axi_awvalid && ~start_single_burst_write && ~burst_write_active) begin start_single_burst_write <= 1'b1; end else begin start_single_burst_write <= 1'b0; //Negate to generate a pulse end end INIT_READ: // This state is responsible to issue start_single_read pulse to // initiate a read transaction. Read transactions will be // issued until burst_read_active signal is asserted. // read controller if (reads_done) begin mst_exec_state <= INIT_COMPARE; end else begin mst_exec_state <= INIT_READ; if (~axi_arvalid && ~burst_read_active && ~start_single_burst_read) begin start_single_burst_read <= 1'b1; end else begin start_single_burst_read <= 1'b0; //Negate to generate a pulse end end INIT_COMPARE: // This state is responsible to issue the state of comparison // of written data with the read data. If no error flags are set, // compare_done signal will be asseted to indicate success. //if (~error_reg) begin ERROR <= error_reg; mst_exec_state <= IDLE; compare_done <= 1'b1; end default : begin mst_exec_state <= IDLE; end endcase end end //MASTER_EXECUTION_PROC
NO.11----突发读写状态管理：
burst_write_active：突发写有效信号，其拉高即表示，正在进行一次突发写过程
burst_read_active：突发读有效信号，其拉高即表示，正在进行一次突发读过程
writes_done：全部写事务完成信号，完成所有写事务后将其拉高
reads_done：全部读事务完成信号，完成所有读事务后将其拉高
// burst_write_active signal is asserted when there is a burst write transaction
// is initiated by the assertion of start_single_burst_write. burst_write_active
// signal remains asserted until the burst write is accepted by the slave
always @(posedge M_AXI_ACLK)
begin
if (M_AXI_ARESETN == 0 || init_txn_pulse == 1'b1)
burst_write_active <= 1'b0;
//The burst_write_active is asserted when a write burst transaction is initiated
else if (start_single_burst_write)
burst_write_active <= 1'b1;
else if (M_AXI_BVALID && axi_bready)
burst_write_active <= 0;
end
// Check for last write completion.
// This logic is to qualify the last write count with the final write
// response. This demonstrates how to confirm that a write has been
// committed.
always @(posedge M_AXI_ACLK)
begin
if (M_AXI_ARESETN == 0 || init_txn_pulse == 1'b1)
writes_done <= 1'b0;
//The writes_done should be associated with a bready response
//else if (M_AXI_BVALID && axi_bready && (write_burst_counter == {(C_NO_BURSTS_REQ-1){1}}) && axi_wlast)
else if (M_AXI_BVALID && (write_burst_counter[C_NO_BURSTS_REQ]) && axi_bready)
writes_done <= 1'b1;
else
writes_done <= writes_done;
end
// burst_read_active signal is asserted when there is a burst write transaction
// is initiated by the assertion of start_single_burst_write. start_single_burst_read
// signal remains asserted until the burst read is accepted by the master
always @(posedge M_AXI_ACLK)
begin
if (M_AXI_ARESETN == 0 || init_txn_pulse == 1'b1)
burst_read_active <= 1'b0;
//The burst_write_active is asserted when a write burst transaction is initiated
else if (start_single_burst_read)
burst_read_active <= 1'b1;
else if (M_AXI_RVALID && axi_rready && M_AXI_RLAST)
burst_read_active <= 0;
end
// Check for last read completion.
// This logic is to qualify the last read count with the final read
// response. This demonstrates how to confirm that a read has been
// committed.
always @(posedge M_AXI_ACLK)
begin
if (M_AXI_ARESETN == 0 || init_txn_pulse == 1'b1)
reads_done <= 1'b0;
//The reads_done should be associated with a rready response
//else if (M_AXI_BVALID && axi_bready && (write_burst_counter == {(C_NO_BURSTS_REQ-1){1}}) && axi_wlast)
else if (M_AXI_RVALID && axi_rready && (read_index == C_M_AXI_BURST_LEN-1) && (read_burst_counter[C_NO_BURSTS_REQ]))
reads_done <= 1'b1;
else
reads_done <= reads_done;
end
// Add user logic here
// User logic ends
endmodule3、仿真波形
接下来使用Vivado自带的仿真器来进行仿真，观看仿真结果。
3.1、AXI4-Full总线的仿真波形
我们先把自动生成的仿真信号删除，添加如下的波形信号：
仿真结果如下：
可以看到仿真结果是用这个彩条+字符的形式表示的，非常清晰。这就是添加了AXI VIP IP的效果。
在AXI4-Full总线上共发生了多个事务：先是多个写事务，接着多个读事务。下面的五个通道分别示意了此时通道内执行的握手操作，将鼠标放在其中任意一处上（以最后一个写事务为例），会出现如下信息（顺序64、地址‘h40000FC0、突发类型递增突发、突发长度16、突发大小4 BYTES等）：
在左键点击，会显示具体的事务流程如下：写地址----写数据----写响应。
再把鼠标放到最后一次读事务上，观察读事务的相关信息，如下：
可以看到，最后一次读事务的相关信息与最后一次写事务的相关信息是一致的，这表示写入数据与读出数据理论上一致。
再点击这次读事务，观察其实现过程：读地址----读数据（包含读响应）。
3.2、主机IP的master接口仿真波形
看完了AXI4-Full总线的仿真波形，我们再看下上面具体解析代码（可以理解为底层驱动）的仿真波形。按如下方法添加：
将信号按通道或用途做好分类，写事务（一共有64次写事务，限于篇幅，仅截图2次写事务）的仿真结果如下：
读事务（一共有64次读事务，限于篇幅，仅截图2次读事务）的仿真结果如下：
写入的数据与读出的数据一致。
4、其他
可以看到其实AXI4-Full总线的使用还是相对比较简单的，只要设计好各个通道的握手时序，以及读写的时序关系就好了。AXI4这个系列暂时就结束了。
