2-3-06 AXI4总线axi-stream总线协议

软件版本：vitis2021.1(vivado2021.1)

操作系统：WIN10 64bit

硬件平台：适用XILINX A7/K7/Z7/ZU/KU系列FPGA

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1概述

AXI4-Stream去掉了地址，允许无限制的数据突发传输规模，AXI4-Stream接口在数据流传输中应用非常方便，本来首先介绍了AXI4-Stream协议的型号定义，并且给出了一些Stream接口的时序方案图。之后通过VIVADO自带的AXI4模板，创建axi-stream-master和axi-stream-slave ip。通过图形设计连线，添加仿真激励完成验证。

本文实验目的：

1:掌握基于VIVADO工具产生AXI协议模板

2:掌握通过VIVADO工具产生AXI-Stream代码

3:掌握通过VIVADO封装AXI-Stream图形化IP

4:通过仿真验证AXI-Stream IP的工作是否正常。

2 AXI4-Stream协议介绍2.1信号定义

信号	源	描述
ACLK	时钟源	信号在ACLK信号上升沿采样
ARESETn	复位源	复位信号,ARESETn低电平有效
TVALID	master	TVALID代表主设备数据有效，当TVALID和TREADY同时有效完成数据收发
TREADY	slave	TREADY表示从设备准备可以，主设备可以发送数据，当TVALID和TREADY同时有效完成数据收发
TDATA[(8n-1):0]	master	TDATA axi-stream的数据
TSTRB[(n-1)：0]	master	TSTRB[n-1:0]对应的bit位为1代表对应的字节有效，否则无效，但是会占用这个数据位。
TKEEP[(n-1)：0]	master	KEEP[n-1:0]对应的bit位为1代表对应的字节有效，否则为空，可以丢掉。
TLAST	master	TLAST代表最后一个数据。
TID[(i-1):0]	master	TID是数据流的标识符，用来表明不同的数据流。
TDEST[(d-1):0]	master	TDEST为据流提供路由信息。
TUSER[(n-1):0]	master	TUSER一般用于数据的同步，代表stream数据的开始。

以上所有信号，在axi-stream传输中，不一定全部用到，具体根据应用场景的情况而定。

2.2 axi-stream方案展示

下图中除了ACLK外，axi-stream的信号用到了，TVALID、TREADY、TLAST、TDATA。其中TDATA虽然是12bit但是实际上会占用16bit的物理总线。并且数据是循环发送，用TLAST标识了一次循环的最后一个数据。

下图中截图来自AXI-DMA mm2s接口的时序图，除了ACLK外，axi-stream的信号用到了，TVALID、TREADY、TLAST、TDATA、TKEEP。用TLAST标识了一次循环的最后一个数据。

下图中是来自于xilinx vivado自带的axis_vid_out ip的视频输出时序。EOL就是tlast ，SOF就是tuser初次外还包括了VALID、READY、DATA信号。

3创建axi-stream-slave总线接口IP

新建fpga工程，过程省略

4创建axi-stream-master总线接口IP

未来完成axi-steam协议的验证，采用以上方法，我们再创建一个saxis的IP

创建完成后如下图所示

5创建FPGA图像化设计

设置IP路径

添加已经创建好的IP

输入关键词axis，在最后可以看到，双击添加Ip

完成连线

maxis的ip参数设置

saxis的ip参数设置

自动创建顶层文件

6创建仿真文件

仿真程序非常简单，只要提供时钟和复位信号

`timescale 1ns / 1ns

module axis_top_sim();

reg m00_axis_aclk_0;

reg m00_axis_aresetn_0;

system_wrappertem system_wrapper_inst

(

.m00_axis_aclk_0(m00_axis_aclk_0),

.m00_axis_aresetn_0(m00_axis_aresetn_0)

);

initial begin

m00_axis_aclk_0 = 1'b0;

m00_axis_aresetn_0 = 1'b0;

#100;

m00_axis_aresetn_0 = 1'b1;

end

always

begin

#5 m00_axis_aclk_0 = ~m00_axis_aclk_0;

end

endmodule

7程序分析

默认的maxis模板的代码有bug，我们对其进行修改。

1:把以下代码替换默认的代码并且保存

`timescale 1 ns / 1 ps

module maxis_v1_0_M00_AXIS #

(

// Width of S_AXIS address bus. The slave accepts the read and write addresses of width C_M_AXIS_TDATA_WIDTH.

parameter integer C_M_AXIS_TDATA_WIDTH = 32,

// Start count is the number of clock cycles the master will wait before initiating/issuing any transaction.

parameter integer C_M_START_COUNT = 32

)

(

// Global ports

input wire M_AXIS_ACLK,

//

input wire M_AXIS_ARESETN,

// Master Stream Ports. TVALID indicates that the master is driving a valid transfer, A transfer takes place when both TVALID and TREADY are asserted.

output wire M_AXIS_TVALID,

// TDATA is the primary payload that is used to provide the data that is passing across the interface from the master.

output wire [C_M_AXIS_TDATA_WIDTH-1 : 0] M_AXIS_TDATA,

// TSTRB is the byte qualifier that indicates whether the content of the associated byte of TDATA is processed as a data byte or a position byte.

output wire [(C_M_AXIS_TDATA_WIDTH/8)-1 : 0] M_AXIS_TSTRB,

// TLAST indicates the boundary of a packet.

output wire M_AXIS_TLAST,

// TREADY indicates that the slave can accept a transfer in the current cycle.

input wire M_AXIS_TREADY

);

// Total number of output data

localparam NUMBER_OF_OUTPUT_WORDS = 8;

// 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

// WAIT_COUNT_BITS is the width of the wait counter.

localparam integer WAIT_COUNT_BITS = clogb2(C_M_START_COUNT-1);

// bit_num gives the minimum number of bits needed to address 'depth' size of FIFO.

localparam bit_num = clogb2(NUMBER_OF_OUTPUT_WORDS);

// Define the states of state machine

// The control state machine oversees the writing of input streaming data to the FIFO,

// and outputs the streaming data from the FIFO

parameter [1:0] IDLE = 2'b00, // This is the initial/idle state

INIT_COUNTER = 2'b01, // This state initializes the counter, once

// the counter reaches C_M_START_COUNT count,

// the state machine changes state to SEND_STREAM

SEND_STREAM = 2'b10; // In this state the

// stream data is output through M_AXIS_TDATA

// State variable

reg [1:0] mst_exec_state;

// Example design FIFO read pointer

reg [bit_num-1:0] read_pointer;

// AXI Stream internal signals

//wait counter. The master waits for the user defined number of clock cycles before initiating a transfer.

reg [WAIT_COUNT_BITS-1 : 0] count;

//streaming data valid

wire axis_tvalid;

//Last of the streaming data

wire axis_tlast;

wire tx_en;

//The master has issued all the streaming data stored in FIFO

wire tx_done;

// I/O Connections assignments

assign M_AXIS_TVALID = axis_tvalid;

assign M_AXIS_TDATA = read_pointer;

assign M_AXIS_TLAST = axis_tlast;

assign M_AXIS_TSTRB = {(C_M_AXIS_TDATA_WIDTH/8){1'b1}};

// Control state machine implementation

always @(posedge M_AXIS_ACLK)

begin

if (!M_AXIS_ARESETN)

// Synchronous reset (active low)

begin

mst_exec_state <= IDLE;

count <= 0;

end

else

case (mst_exec_state)

IDLE:

mst_exec_state <=

INIT_COUNTER:

// The slave starts accepting tdata when

// there tvalid is asserted to mark the

// presence of valid streaming data

if ( count == C_M_START_COUNT - 1 )

begin

mst_exec_state <= SEND_STREAM;

end

else

begin

count <= count + 1;

mst_exec_state <= INIT_COUNTER;

end

SEND_STREAM:

// The example design streaming master functionality starts

// when the master drives output tdata from the FIFO and the slave

// has finished storing the S_AXIS_TDATA

if (tx_done)

begin

mst_exec_state <= IDLE;

end

else

begin

mst_exec_state <= SEND_STREAM;

end

endcase

end

//tvalid generation

//axis_tvalid is asserted when the control state machine's state is SEND_STREAM and

//number of output streaming data is less than the NUMBER_OF_OUTPUT_WORDS.

assign axis_tvalid = ((mst_exec_state == SEND_STREAM) && (read_pointer < NUMBER_OF_OUTPUT_WORDS));

// AXI tlast generation

assign axis_tlast = (read_pointer == NUMBER_OF_OUTPUT_WORDS - 1'b1)&& tx_en;

assign tx_done = axis_tlast;

//FIFO read enable generation

assign tx_en = M_AXIS_TREADY && axis_tvalid;

// Streaming output data is read from FIFO

always @( posedge M_AXIS_ACLK )

begin

if(!M_AXIS_ARESETN)

begin

read_pointer <= 0;

end

else if (tx_en)

begin

read_pointer <= read_pointer + 32'b1;

end

endmodule

2:在Tcl Console中输入reset_project对工程IP复位

3:之后单击Refresh IP Catalog

最后单击upgrade Selected完成更新

在看saxis的源码，这部分代码非常简单

首先是状态机，当S_AXI_TVALID有效，saxis的状态机进入WRITE_FIFO

只要接收的数据小于(write_pointer <= NUMBER_OF_INPUT_WORDS-1)并且saxis状态机是WRITE_FIFO状态机，表示saxis可以接收数据，设置axis_tready==1如下：assign axis_tready = ((mst_exec_state == WRITE_FIFO) && (write_pointer <= NUMBER_OF_INPUT_WORDS-1));

write_pointer 用于写入了多少个数据。

写数据到fifo中

8实验结果

仿真结果

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