目录
前言
代码解析
前言
在我学习过程中遇到了第一个认知上的门槛：AXI协议。试想一个场景：我PL端的IP要通过AXI-Full协议给PS端传输数据，我该怎么做？
首先肯定是创建一个带有AXI-Full-Matser的接口
下一步，Xilinx官方会给我们一个接口的实例文件：
顶层是一个对外的接口，而内层的代码则是AXI-Full-Master接口的协议实现。当然了，我们肯定是要通过改动这个文件来将我们自己的IP和AXI接口协议相结合，因此我们有必要读懂AXI-Full-Master的代码内容。
代码解析
实际上Xilinx官方给的这个例子是一个AXI-Full-Master读写的例子，一共900多行，主要是描述一个带有AXI-Master接口的IP要如何进行数据的读写。
相当于描述了一个这样的状态机，初始化完之后先开始写，再开始读，并且把读出的数据和写入的比较，如果没有错误即可开始新一轮的写。
代码具有参考加载，能够指导我们编写符合AXI协议规范的IP。
我将英文翻译成为中文，供各位研究，同时红色部分是我重点标出来，可供大家思考与改造。
`timescale 1 ns / 1 ps
module M_AXI_Test1_v1_0_M_AXI #
(
// 目标从机基地址
parameter C_M_TARGET_SLAVE_BASE_ADDR = 32'h40000000,
// 突发长度. 支持 1, 2, 4, 8, 16, 32, 64, 128, 256
parameter integer C_M_AXI_BURST_LEN = 16,
// 线程ID宽度
parameter integer C_M_AXI_ID_WIDTH = 1,
// 地址总线宽度
parameter integer C_M_AXI_ADDR_WIDTH = 32,
// 数据总线宽度
parameter integer C_M_AXI_DATA_WIDTH = 32,
// 用户写地址总线宽度
parameter integer C_M_AXI_AWUSER_WIDTH = 0,
// 用户读地址总线宽度
parameter integer C_M_AXI_ARUSER_WIDTH = 0,
// 用户写数据总线宽度
parameter integer C_M_AXI_WUSER_WIDTH = 0,
// 用户读数据总线宽度
parameter integer C_M_AXI_RUSER_WIDTH = 0,
// 用户应答总线宽度
parameter integer C_M_AXI_BUSER_WIDTH = 0
)
(
/*
端口定义块，该模块定义了AXI-Full-Master的各个接口，包括了：
1、时钟、复位、传输状态标志、AXI接口ID、用户自定义通道
2、写数据通道（写地址、写数据、写响应）
3、读数据通道（读地址、读数据）
*/
// AXI启动线
input wire INIT_AXI_TXN, //异步信号
// 当传输完成时置位
output wire TXN_DONE,
// 当检测到错误时置位
output reg ERROR,
// 全局时钟信号
input wire M_AXI_ACLK,
// 全局复位信号，低电平有效
input wire M_AXI_ARESETN,
/*写通道信号*/
// 主机接口写地址ID
output wire [C_M_AXI_ID_WIDTH-1 : 0] M_AXI_AWID,
// 突发长度. （The burst length gives the exact number of transfers in a burst）
output wire [7 : 0] M_AXI_AWLEN,
// 突发传输的大小. （This signal indicates the size of each transfer in the burst）
output wire [2 : 0] M_AXI_AWSIZE,
// 突发类型. （The burst type and the size information）,
// determine how the address for each transfer within the burst is calculated。
//决定了每次突发传输的地址是怎样计算出的
output wire [1 : 0] M_AXI_AWBURST,
// Lock type. Provides additional information about the
// atomic characteristics of the transfer.
//锁定类型，提供关于传输的原子特征的附加信息
output wire M_AXI_AWLOCK,
// 存储类型. This signal indicates how transactions
// are required to progress through a system.
//这个信号指示了数据传输如何在系统中进行
output wire [3 : 0] M_AXI_AWCACHE,
// 保护类型. This signal indicates the privilege ，
// and security level of the transaction, and whether
// the transaction is a data access or an instruction access.
//这个信号指示了传输的权限和安全等级，以及传输的内容是数据还是指令
output wire [2 : 0] M_AXI_AWPROT,
// 服务质量, QoS identifier sent for each write transaction.
//为每个写事务发送的QoS标识符。
output wire [3 : 0] M_AXI_AWQOS,
// Optional User-defined signal in the write address channel.
//可选写地址通道中的自定义信号
output wire [C_M_AXI_AWUSER_WIDTH-1 : 0] M_AXI_AWUSER,
//写地址信号组
//主机接口写地址
output wire [C_M_AXI_ADDR_WIDTH-1 : 0] M_AXI_AWADDR,
// 写地址有效 This signal indicates that
// the channel is signaling valid write address and control information.
//该信号指示该通道正在发送有效的写地址和控制信息
output wire M_AXI_AWVALID,
// 写地址准备. This signal indicates that
// the slave is ready to accept an address and associated control signals
//该信号指示从机已经准备好接收地址和相关控制信号
input wire M_AXI_AWREADY,
//写数据信号组
// 主机写数据接口
output wire [C_M_AXI_DATA_WIDTH-1 : 0] M_AXI_WDATA,
// 写选通. This signal indicates which byte
// lanes hold valid data. There is one write strobe
// bit for each eight bits of the write data bus.
//这个信号指示了哪些字节通道保持有效数据，在写数据总线中，每八位数据对应一个写选通位
output wire [C_M_AXI_DATA_WIDTH/8-1 : 0] M_AXI_WSTRB,
// 上一次写信号. This signal indicates the last transfer in a write burst.
//这个信号指示了在指示写突发中的最后一次传输
output wire M_AXI_WLAST,
// Optional User-defined signal in the write data channel.
//可选写数据通道中的自定义信号
output wire [C_M_AXI_WUSER_WIDTH-1 : 0] M_AXI_WUSER,
// 写有效信号. This signal indicates that valid write
// data and strobes are available
//此信号指示了写数据和选通信号有效
output wire M_AXI_WVALID,
// 写准备信号. This signal indicates that the slave
// can accept the write data.
//该信号指示从机已经准备好接收写入的数据
input wire M_AXI_WREADY,
//写响应信号组
// Master Interface Write Response.
input wire [C_M_AXI_ID_WIDTH-1 : 0] M_AXI_BID,
// 写响应信号. This signal indicates the status of the write transaction.
//该信号指示写传输的状态
input wire [1 : 0] M_AXI_BRESP,
// Optional User-defined signal in the write response channel
//可选写响应通道中的自定义信号
input wire [C_M_AXI_BUSER_WIDTH-1 : 0] M_AXI_BUSER,
// 写响应有效. This signal indicates that the
// channel is signaling a valid write response.
//该信号指示通道正在发送有效的写响应
input wire M_AXI_BVALID,
// 响应准备信号. This signal indicates that the master
// can accept a write response.
//该信号指示主机可以接收写响应信号
/*读数据通道*/
output wire M_AXI_BREADY,
// 主机接口读地址ID.
output wire [C_M_AXI_ID_WIDTH-1 : 0] M_AXI_ARID,
// 突发长度. The burst length gives the exact number of transfers in a burst
output wire [7 : 0] M_AXI_ARLEN,
// 突发大小. This signal indicates the size of each transfer in the burst
output wire [2 : 0] M_AXI_ARSIZE,
// 突发类型. 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,
//锁定类型. Provides additional information about the
// atomic characteristics of the transfer.
output wire M_AXI_ARLOCK,
// 存储类型. This signal indicates how transactions
// are required to progress through a system.
output wire [3 : 0] M_AXI_ARCACHE,
// 保护类型. 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,
// 服务质量, 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,
//读地址信号组
// 读地址. This signal indicates the initial
// address of a read burst transaction.
//该信号指示突发读的起始地址
output wire [C_M_AXI_ADDR_WIDTH-1 : 0] M_AXI_ARADDR,
// 写入地址有效. This signal indicates that
// the channel is signaling valid read address and control information
//该信号指示通道正在发送有效的读地址以及相关控制信号
output wire M_AXI_ARVALID,
//读地址准备信号. This signal indicates that
// the slave is ready to accept an address and associated control signals
//该信号指示从机已经准备好接收地址和控制信号
input wire M_AXI_ARREADY,
//读数据信号组
// 读ID标签. This signal is the identification tag
// for the read data group of signals generated by the slave.
//该信号是由从机产生的信号的读数据组的身份标签
input wire [C_M_AXI_ID_WIDTH-1 : 0] M_AXI_RID,
// 主机读数据接口
input wire [C_M_AXI_DATA_WIDTH-1 : 0] M_AXI_RDATA,
// 读响应信号. This signal indicates the status of the read transfer
input wire [1 : 0] M_AXI_RRESP,
// 最后一次读信号. This signal indicates the last transfer in a read burst
input wire M_AXI_RLAST,
// Optional User-defined signal in the read address channel.
//可选读地址通道中的自定义信号
input wire [C_M_AXI_RUSER_WIDTH-1 : 0] M_AXI_RUSER,
// 读有效信号. This signal indicates that the channel
// is signaling the required read data.
input wire M_AXI_RVALID,
// 读准备信号. This signal indicates that the master can
// accept the read data and response information.
output wire M_AXI_RREADY
);
/* 功能模块，用来根据数据大小计算数据位数 */
// 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.
//C_TRANSACTIONS_NUM 是读写传输中的 传输数据个数计数器的宽度 ,C_M_AXI_BURST_LEN是突发长度，即一次突发传输数据的个数。
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.
//突发传输长度，0到2^n的长度最终会对4K的地址范围内突发传输
localparam integer C_MASTER_LENGTH = 12; //即4K的数据的长度（最大）
// total number of burst transfers is master length divided by burst length and burst size
//突发传输的总数由突发传输大小和尺寸共同决定，C_NO_BURSTS_REQ这个值是突发传输次数计数器的位宽。
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.
/*
这里给出一个状态机的例子，该状态机的功能为：
1、初始化计数器
2、初始化读写传输
3、初始化读写数据比较
*/
//状态
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
//当INIT_AXI_TXN从0变到1时，状态机从该状态转移到下一个状态，并且初始化AXI4Lite
INIT_WRITE = 2'b01, // This state initializes write transaction,
// once writes are done, the state machine
// changes state to INIT_READ
//这个状态初始化写传输，并且，当写操作完成时，该状态将切换到 下一个状态（初始化读）
INIT_READ = 2'b10, // This state initializes read transaction
// once reads are done, the state machine
// changes state to INIT_COMPARE
//该状态将初始化读传输，并且，当读操作完成时，状态机将会跳转到下一个状态（比较状态）
INIT_COMPARE = 2'b11; // This state issues the status of comparison
// of the written data with the read data
//该状态指示 写入的数据和读到的数据进行比较的结果
reg [1:0] mst_exec_state; //状态变量
// AXI4LITE signals
//AXI4 internal temp signals
//AXI4内部临时暂存变量
reg [C_M_AXI_ADDR_WIDTH-1 : 0] axi_awaddr; //地址
reg axi_awvalid;
reg [C_M_AXI_DATA_WIDTH-1 : 0] axi_wdata; //数据
reg axi_wlast; //写数据突发完成标志
reg axi_wvalid; //写有效信号
reg axi_bready; //写响应准备信号
reg [C_M_AXI_ADDR_WIDTH-1 : 0] axi_araddr;//读地址
reg axi_arvalid; //读地址有效
reg axi_rready; //读准备信号
//write beat count in a burst
//突发写节拍计数值，突发传输中，每传输一个数据，计数值加一，用于指示突发传输的进度
reg [C_TRANSACTIONS_NUM : 0] write_index;
//read beat count in a burst
//突发读节拍计数值
reg [C_TRANSACTIONS_NUM : 0] read_index;
//size of C_M_AXI_BURST_LEN length burst in bytes
//一次突发传输长度的大小(以字节为单位)
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.
//突发计数器是用来跟踪传输 2^C_MASTER_LENGTH字节数据所需的 C_M_AXI_BURST_LEN突发长度的突发传输数量，也就是说完成一次突发传输值会加1，满了说明已经传输了4K的地址数据了。
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
//接口响应错误标志
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;
// I/O Connections assignments
//输入输出接口赋值
//I/O Connections. Write Address (AW)
//写地址IO连接
assign M_AXI_AWID = 'b0;//ID号
//The AXI address is a concatenation of the target base address + active offset range
//AXI的地址是 目标基址+活动偏移范围
assign M_AXI_AWADDR = C_M_TARGET_SLAVE_BASE_ADDR + axi_awaddr;
//Burst LENgth is number of transaction beats, minus 1
//突发长度是传输的节拍数，最小为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
//突发传输大小应该是 数据总线宽度, 2^ Size字节，否则使用窄突发
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.
//如果要通过Zynq ACP端口使用一致性访问，则将值更新为4’b0011。不可分配，不可修改，不可缓冲。不可缓冲，因为此示例用于测试内存，而不是中间缓存。
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)
//写数据
assign M_AXI_WDATA = axi_wdata;
//All bursts are complete and aligned in this example
//在该示例中，所有的突发传输都是完整且对齐的
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)
//写响应
assign M_AXI_BREADY = axi_bready;
//Read Address (AR)
//读地址
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
//实例所设计的IO
assign TXN_DONE = compare_done;
//Burst size in bytes
//突发大小（以字节为单位）
assign burst_size_bytes = C_M_AXI_BURST_LEN * C_M_AXI_DATA_WIDTH/8;
assign init_txn_pulse = (!init_txn_ff2) && init_txn_ff;
//Generate a pulse to initiate AXI transaction.
//产生一个脉冲来初始化AXI传输
always @(posedge M_AXI_ACLK)
begin
// Initiates AXI transaction delay
if (M_AXI_ARESETN == 0 ) //复位信号有效
begin
init_txn_ff <= 1'b0;
init_txn_ff2 <= 1'b0;
end
else //正常情况，准备状态
begin
init_txn_ff <= INIT_AXI_TXN; //外接AXI启动线
init_txn_ff2 <= init_txn_ff;
end
end
//--------------------
//Write Address Channel
//--------------------
// The purpose of the write address channel is to request the address and
// command information for the entire transaction. It is a single beat
// of information.
// The AXI4 Write address channel in this example will continue to initiate
// write commands as fast as it is allowed by the slave/interconnect.
// The address will be incremented on each accepted address transaction,
// by burst_size_byte to point to the next address.
//写地址通道；
/*
写地址通道的目的在于请求传输所需要的地址信息和命令信息。这是一个单节拍的信息
在这个例子中，AXI4写地址通道将会不断初始化写命令，直到从机响应连接
并且将通过burst_size_byte，自动指向下一个地址
*/
/* 译者注：该触发器块主要对axi_awvaild这个信号赋值，也就是地址有效信号 */
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
// 如果之前无效，则启动下一个传输
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 */
/*有效信号一旦置位，就必须保持，因此axi_awvalid
必须一直保持直到传输完成*/
else if (M_AXI_AWREADY && axi_awvalid) //ready信号和valid信号同时有效，则下一个时钟沿传输完成。
begin
axi_awvalid <= 1'b0;
end
else //否则一直保持
axi_awvalid <= axi_awvalid;
end
// Next address after AWREADY indicates previous address acceptance
// 译者注：该模块主要对axi_awaddr信号赋值用于突发传输时控制地址递增，修改该模块可以操作写地址
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) //前一次传输完成
begin
axi_awaddr <= axi_awaddr + burst_size_bytes; //每次地址增加burst_size_bytes
end
else
axi_awaddr <= axi_awaddr;
end
//--------------------
//Write Data Channel
//--------------------
//The write data will continually try to push write data across the interface.
//The amount of data accepted will depend on the AXI slave and the AXI
//Interconnect settings, such as if there are FIFOs enabled in interconnect.
//Note that there is no explicit timing relationship to the write address channel.
//The write channel has its own throttling flag, separate from the AW channel.
//Synchronization between the channels must be determined by the user.
//The simpliest but lowest performance would be to only issue one address write
//and write data burst at a time.
//In this example they are kept in sync by using the same address increment
//and burst sizes. Then the AW and W channels have their transactions measured
//with threshold counters as part of the user logic, to make sure neither
//channel gets too far ahead of each other.
//Forward movement occurs when the write channel is valid and ready
//写数据通道
/* 写数据通道将会不停地尝试通过接口写数据
接收的数据量取决于AXI从设备以及AXI互联的设置，例如，互联是否使能FIFO等
注意，写数据通道和和写地址通道没有明确的时序关系，写通道有自己的 throttling flag，和写地址通道隔离，
通道之间的同步必须由用户决定。
最简单，也是性能最低的情况是只发出一个地址写和写数据突发一次。
在本例子中，地址和数据通过使用相同的地址增量和相同的突发尺寸保持同步
然后，AW和W通道使用阈值计数器作为用户逻辑的一部分来度量它们的事务，以确保任何通道都不会彼此超前太远。
当写通道有效且准备就绪时发生向前移动。
*/
/*译者注：该模块主要功能是按照协议内容对axi_wvalid进行赋值*/
assign wnext = M_AXI_WREADY & axi_wvalid; //当一次传输完成后，wnext置位
// 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
/* 该模块主要控制wlast，指示突发传输完成 */
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 */
/*译者注：该部分主要对write_index赋值，突发传输数据个数计数器*/
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 */
/*译者注：该模块功能为写数据产生，数据内容 就是从0开始增加的计数值，修改该模块可以操作写入的数据*/
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
//----------------------------
//Write Response (B) Channel
//----------------------------
//The write response channel provides feedback that the write has committed
//to memory. BREADY will occur when all of the data and the write address
//has arrived and been accepted by the slave.
//The write issuance (number of outstanding write addresses) is started by
//the Address Write transfer, and is completed by a BREADY/BRESP.
//While negating BREADY will eventually throttle the AWREADY signal,
//it is best not to throttle the whole data channel this way.
//The BRESP bit [1] is used indicate any errors from the interconnect or
//slave for the entire write burst. This example will capture the error
//into the ERROR output.
/* 写响应通道
写响应通道提供来自从机的写反馈。BREADY信号将会在从机接收到所有的地址和数据之后有效。
写发送（未完成的写地址数量）由地址写传输启动，并由一个BREADY/BRESP完成。
*/
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];
//----------------------------
//Read Address Channel
//----------------------------
//The Read Address Channel (AW) provides a similar function to the
//Write Address channel- to provide the tranfer qualifiers for the burst.
//In this example, the read address increments in the same
//manner as the write address channel.
//读地址通道，功能和写地址通道相似--提供对突发传输的控制
//在这个例子中，读地址增量与写地址通道的方式相同。
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
//ARREADY后的下一个地址表示之前的地址接受 ，修改该模块可以操作读取数据的地址
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
//--------------------------------
//Read Data (and Response) Channel
//--------------------------------
//读数据通道
// Forward movement occurs when the channel is valid and ready
//当通道有效且准备就绪时发生向前移动
assign rnext = M_AXI_RVALID && axi_rready;
// Burst length counter. Uses extra counter register bit to indicate
// terminal count to reduce decode logic
//突发传输数据个数计数器
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
读数据通道返回读请求的结果
In this example the data checker is always able to accept
more data, so no need to throttle the RREADY signal
这个例子中，数据检查器总是能够接收更多的数据，所以没有必要抑制RREADY信号
*/
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
//当 M_AXI_RVALID 被从机置位时，master使用axi_rready接受/确认rdata/rresp
// 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
//将接收到的数据和生成的数据比较 ，修改该模块，可以保存读出的数据 （M_AXI_RDATA）
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
//只有当RVALID有效时检查数据
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
//标记任何读响应错误
assign read_resp_error = axi_rready & M_AXI_RVALID & M_AXI_RRESP[1];
//----------------------------------------
//Example design read check data generator
//-----------------------------------------
//示例设计了一个读取检查数据生成器
//Generate expected read data to check against actual read data
//生成预期的读数据，以对照实际的读数据进行检查
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
//----------------------------------
//实例设计了一个错误寄存器，注册并保存任何数据不匹配或读写接口错误
//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) //不匹配错误，写响应错误，读响应错误
begin
error_reg <= 1'b1;
end
else
error_reg <= error_reg;
end
//--------------------------------
//Example design throttling
//--------------------------------
// For maximum port throughput, this user example code will try to allow
// each channel to run as independently and as quickly as possible.
// However, there are times when the flow of data needs to be throtted by
// the user application. This example application requires that data is
// not read before it is written and that the write channels do not
// advance beyond an arbitrary threshold (say to prevent an
// overrun of the current read address by the write address).
// From AXI4 Specification, 13.13.1: "If a master requires ordering between
// read and write transactions, it must ensure that a response is received
// for the previous transaction before issuing the next transaction."
// This example accomplishes this user application throttling through:
// -Reads wait for writes to fully complete
// -Address writes wait when not read + issued transaction counts pass
// a parameterized threshold
// -Writes wait when a not read + active data burst count pass
// a parameterized threshold
// 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
//implement master command interface state machine
//实现一个状态机，在读写验证之间切换状态
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.
//该状态负责等待用户定义 C_M_START_COUNT的时钟周期数
if ( init_txn_pulse == 1'b1) //初始化信号有效时
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
//该状态负责发送写起始信号，初始化写操作。当 burst_write_active signal 被置位后写操作将启动。
if (writes_done) //写操作完了之后，跳转到读状态
begin
mst_exec_state <= INIT_READ;//
end
else
begin
mst_exec_state <= INIT_WRITE; //否则等待
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
//该状态负责发送 start_single_read 脉冲来初始化读操作。当burst_read_active signal 被置位后读操作开始。
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)
//该状态负责发送写入的数据和读出的数据的比较结果，如果没有错误 compare_done 信号将会被置为用来指示传输成功。
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
//下面这几个触发器，主要功能就是对前面提到的 burst_write_active，burst_read_active和writes_done reads_done等信号进行一个控制
// 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文章来源：https://www.toymoban.com/news/detail-678414.html
endmodule文章来源地址https://www.toymoban.com/news/detail-678414.html
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