AXI4总线协议 ------ AXI

一、AXI 相关知识介绍

https://download.csdn.net/download/mvpkuku/90841873 AXI_LITE

选出部分重点，详细文档见上面链接。

1.AXI4 协议类型

2.握手机制

二、AXI_LITE 协议的实现

1. AXI_LITE 通道及各通道端口功能介绍

2.实现思路及框架

2.1 总体框架

2.2 写通道

1.复位信号进行跨时钟域同步（用户时钟/AXI4时钟）

2.仅当user_wr_ready为高时，用户的写通道是有效的

3.例化两个fifo分别存储用户端传来的地址以及数据用户时钟写入，并通过AXI时钟读出

4.控制AXI_LITE（状态机）接口信号是在AXI时钟下进行（控制cmd_rden/data_rden并输出对应的相关接口数据）

`timescale 1ns / 1ps
//
// Description: AXI_lite写通道
//
module axlite_wr_channel#(parameter USER_WR_DATA_WIDTH    = 32 ,//用户写数据位宽和AXI4—Lite数据位宽保持一致parameter AXI_DATA_WIDTH 		= 32, //AXI4_LITE总线规定，数据位宽只支持32Bit或者64bitparameter AXI_ADDR_WIDTH        = 32	
)(input   wire							        clk,     //用户写时钟		input   wire									axi_clk, //从机读时钟   input   wire									reset,//与 用户端 交互信号input   wire								    user_wr_en,input   wire  [USER_WR_DATA_WIDTH-1:0]	        user_wr_data,input   wire  [AXI_ADDR_WIDTH-1 :0]		        user_wr_addr,output  wire                                    user_wr_ready,	//与 axi_lite从机 交互信号output  reg   [AXI_ADDR_WIDTH -1:0]  	        m_axi_awaddr, //write addr channeloutput  wire  [2:0] 				 	        m_axi_awprot, output  reg   		 				 	        m_axi_awvalid, input   wire    		 			 	        m_axi_awready,output  reg   [AXI_DATA_WIDTH-1:0]	 	        m_axi_wdata,   //write data channeloutput  wire  [AXI_DATA_WIDTH/8-1:0] 	        m_axi_wstrb,output  reg      					 	        m_axi_wvalid,input   wire    					 	        m_axi_wready,input   wire  [1:0]	         	                m_axi_bresp,  //wirte response channelinput   wire	   			         	        m_axi_bvalid,output  wire    			         	        m_axi_bready
);(* dont_touch = "true"*) reg reset_sync_d0;  //user clk
(* dont_touch = "true"*) reg reset_sync_d1;
(* dont_touch = "true"*) reg reset_sync;
(* dont_touch = "true"*) reg a_reset_sync_d0; //axi clk
(* dont_touch = "true"*) reg a_reset_sync_d1;
(* dont_touch = "true"*) reg a_reset_sync;reg	 [31:0]  cmd_din;
reg          cmd_wren;
wire [31:0]  cmd_dout;
reg 		 cmd_rden;
wire		 cmd_wrfull ;
wire		 cmd_rdempty;
wire [4:0]   cmd_wrcount;
wire [4:0]   cmd_rdcount;reg	 [31:0]  data_din;
reg          data_wren;
wire [31:0]  data_dout;
reg 		 data_rden;
wire		 data_wrfull;
wire		 data_rdempty;
wire [4:0]   data_wrcount;
wire [4:0]   data_rdcount;reg [2 : 0]	 cur_status;
reg [2 : 0]	 nxt_status;localparam WR_IDLE     = 3'b000;
localparam WR_PRE      = 3'b001;
localparam WR_DATA_EN  = 3'b010;
localparam WR_END      = 3'b100;
/*--------------------------------------------------*\assign
\*--------------------------------------------------*/
assign m_axi_bready  = 1'b1;
assign m_axi_awprot  = 0;
assign m_axi_wstrb   = {AXI_DATA_WIDTH/8{1'b1}};assign user_wr_ready = reset_sync ? 1'b0 : cmd_wrcount <= 'd12 ; //留一点余量 //当user_wr_ready为低的时候，用户发送写是无效的
/*--------------------------------------------------*\CDC process
\*--------------------------------------------------*/
always @(posedge clk) beginreset_sync_d0   <= reset;reset_sync_d1   <= reset_sync_d0;reset_sync      <= reset_sync_d1;
endalways @(posedge axi_clk) begina_reset_sync_d0 <= reset;a_reset_sync_d1 <= a_reset_sync_d0;a_reset_sync    <= a_reset_sync_d1;
end/*--------------------------------------------------*\wirte addr to cmd fifo、write data to data fifo 
\*--------------------------------------------------*/
always @(posedge clk) beginif (user_wr_ready) begincmd_wren  <= user_wr_en;cmd_din   <= user_wr_addr;data_wren <= user_wr_en;data_din  <= user_wr_data; 		endelse begincmd_wren  <= 0;cmd_din   <= 0;data_wren <= 0;data_din  <= 0; 		end
end/*--------------------------------------------------*\WR state machine  (三段式)
\*--------------------------------------------------*/
always@(posedge axi_clk)beginif(a_reset_sync)cur_status <= WR_IDLE;elsecur_status <= nxt_status;       
endalways@(*)beginif(a_reset_sync)beginnxt_status <= WR_IDLE;endelse begincase(cur_status)WR_IDLE : beginif(!cmd_rdempty)nxt_status <= WR_PRE;elsenxt_status <= cur_status;endWR_PRE : beginnxt_status <= WR_DATA_EN;endWR_DATA_EN : beginif (m_axi_bvalid && m_axi_bready)nxt_status <= WR_END;else nxt_status <= cur_status;end			WR_END : beginnxt_status <= WR_IDLE;enddefault : nxt_status <= WR_IDLE;endcaseend  
end
/*-----------------------------------------------------------*\read addr from cmd_fifo 、 read data from data_fifo  
\*-----------------------------------------------------------*/
always @(*) beginif (a_reset_sync) begincmd_rden   <= 0;data_rden  <= 0;endelse begincmd_rden   <= cur_status == WR_PRE;data_rden  <= cur_status == WR_PRE;end
endalways @(posedge axi_clk) beginif (cmd_rden) m_axi_awaddr <= cmd_dout;else m_axi_awaddr <= m_axi_awaddr;
endalways @(posedge axi_clk) beginif (a_reset_sync) m_axi_awvalid <= 0;else if (cur_status == WR_PRE)m_axi_awvalid <= 1'b1;else if (m_axi_awvalid && m_axi_awready)m_axi_awvalid <= 0;
endalways @(posedge axi_clk) beginif (data_rden) m_axi_wdata <= data_dout;else m_axi_wdata <= m_axi_wdata;
endalways @(posedge axi_clk) beginif (a_reset_sync) m_axi_wvalid <= 0;else if (cur_status == WR_PRE)m_axi_wvalid <= 1'b1;else if (m_axi_wvalid && m_axi_wready)m_axi_wvalid <= 0;
end//写地址fifo
fifo_w32xd16 wr_cmd_fifo (.rst          ( reset_sync  ), // input wire rst.wr_clk       ( clk         ), // input wire wr_clk         用户写时钟.din          ( cmd_din     ), // input wire [31 : 0] din.wr_en        ( cmd_wren    ), // input wire wr_en.rd_clk       ( axi_clk     ), // input wire rd_clk         从机读时钟 .rd_en        ( cmd_rden    ), // input wire rd_en.dout         ( cmd_dout    ), // output wire [31 : 0] dout.full         ( cmd_wrfull  ), // output wire full.empty        ( cmd_rdempty ), // output wire empty.rd_data_count( cmd_wrcount ), // output wire [4 : 0] rd_data_count.wr_data_count( cmd_rdcount )  // output wire [4 : 0] wr_data_count
);//写数据fifo
fifo_w32xd16 wr_data_fifo (.rst          ( reset_sync   ), // input wire rst.wr_clk       ( clk          ), // input wire wr_clk        用户写时钟.din          ( data_din     ), // input wire [31 : 0] din.wr_en        ( data_wren    ), // input wire wr_en.rd_clk       ( axi_clk      ), // input wire rd_clk        从机读时钟 .rd_en        ( data_rden    ), // input wire rd_en.dout         ( data_dout    ), // output wire [31 : 0] dout.full         ( data_wrfull  ), // output wire full.empty        ( data_rdempty ), // output wire empty.rd_data_count( data_rdcount ), // output wire [4 : 0] rd_data_count.wr_data_count( data_wrcount )  // output wire [4 : 0] wr_data_count
);
endmodule

2.3 读通道

读通道的实现分两步，用户端发出读请求并给读的地址，然后从机根据地址发出数据，用户读出。

因此读地址fifo的逻辑部分与写通道一致，只有状态机跳转的RD_DATA_EN的条件根据模块端口有所改变，但是读数据fifo，是在AXI_CLK的时钟域下，端口输入有效及端口输入数据，根据非空开始用户读，然后赋给模块用户端口

`timescale 1ns / 1ps
//
// Description: AXI_LITE读通道
//
module axilite_rd_channel#(parameter USER_RD_DATA_WIDTH    = 32 , //用户读数据位宽和AXI4—Lite数据位宽保持一致parameter AXI_DATA_WIDTH 		= 32, parameter AXI_ADDR_WIDTH        = 32		
)(input   wire								    clk,  	  input   wire								    axi_clk,    input   wire								    reset,//用户端读请求，读地址信号input   wire								    user_rd_en,input   wire  [AXI_ADDR_WIDTH-1 :0]		        user_rd_addr,output  wire                                    user_rd_ready,output  reg   [USER_RD_DATA_WIDTH-1:0]	        user_rd_data,output  reg                                     user_rd_valid,//与AXI_LITE从机 交互信号output  reg   		 							m_axi_arvalid, // axi read address channelinput   wire   		 							m_axi_arready, output  reg   [AXI_ADDR_WIDTH-1:0] 				m_axi_araddr,output  wire  [2:0] 							m_axi_arprot, input   wire  [AXI_DATA_WIDTH-1:0]	    		m_axi_rdata,   // axi read data channelinput   wire  [1:0] 				    		m_axi_resp,input   wire     					    		m_axi_rvalid,output  wire   						   	 		m_axi_rready
);(* dont_touch = "true"*) reg reset_sync_d0;  //user clk
(* dont_touch = "true"*) reg reset_sync_d1;
(* dont_touch = "true"*) reg reset_sync;
(* dont_touch = "true"*) reg a_reset_sync_d0; //axi clk
(* dont_touch = "true"*) reg a_reset_sync_d1;
(* dont_touch = "true"*) reg a_reset_sync;reg	 [31:0]  cmd_din;
reg          cmd_wren;
wire [31:0]  cmd_dout;
reg 		 cmd_rden;
wire		 cmd_wrfull;
wire		 cmd_rdempty;
wire [4:0]   cmd_wrcount;
wire [4:0]   cmd_rdcount;reg	 [31:0]  data_din;
reg          data_wren;
wire [31:0]  data_dout;
wire 		 data_rden;
wire		 data_wrfull;
wire		 data_rdempty;
wire [4:0]   data_wrcount;
wire [4:0]   data_rdcount;reg [2 : 0]	 cur_status;
reg [2 : 0]	 nxt_status;localparam RD_IDLE     = 3'b000;
localparam RD_PRE      = 3'b001;
localparam RD_DATA_EN  = 3'b010;
localparam RD_END      = 3'b100;
/*--------------------------------------------------*\assign
\*--------------------------------------------------*/
assign user_rd_ready = reset_sync ? 1'b0 : cmd_wrcount <= 'd12 ; 
assign m_axi_rready  = 1'b1;
assign m_axi_arprot  = 0;
/*--------------------------------------------------*\CDC process
\*--------------------------------------------------*/
always @(posedge clk) beginreset_sync_d0   <= reset;reset_sync_d1   <= reset_sync_d0;reset_sync      <= reset_sync_d1;
endalways @(posedge axi_clk) begina_reset_sync_d0 <= reset;a_reset_sync_d1 <= a_reset_sync_d0;a_reset_sync    <= a_reset_sync_d1;
end/*--------------------------------------------------*\wirte addr to cmd fifo
\*--------------------------------------------------*/
always @(posedge clk) beginif (user_rd_ready) begincmd_wren  <= user_rd_en;cmd_din   <= user_rd_addr;	endelse begincmd_wren  <= 0;cmd_din   <= 0;			end
end/*--------------------------------------------------*\RD state machine  
\*--------------------------------------------------*/
always @(posedge axi_clk) beginif (a_reset_sync) begincur_status <= RD_IDLE;endelse begincur_status <= nxt_status;end
endalways @(*) beginif (a_reset_sync) beginnxt_status <= RD_IDLE;		endelse begincase(cur_status)RD_IDLE : beginif (~cmd_rdempty)nxt_status <= RD_PRE;else nxt_status <= cur_status;endRD_PRE : beginnxt_status <= RD_DATA_EN;endRD_DATA_EN : beginif (m_axi_rvalid && m_axi_rready)nxt_status <= RD_END;else nxt_status <= cur_status;endRD_END : beginnxt_status <= RD_IDLE;enddefault : nxt_status <= RD_IDLE;endcase	end
end/*-----------------------------------------------------------*\read addr from cmd_fifo 
\*-----------------------------------------------------------*/
always @(*) beginif (a_reset_sync) cmd_rden  <= 0;else cmd_rden  <= cur_status == RD_PRE;
endalways @(posedge axi_clk) beginif (cmd_rden) m_axi_araddr <= cmd_dout;else m_axi_araddr <= m_axi_araddr;
endalways @(posedge axi_clk) beginif (a_reset_sync) m_axi_arvalid <= 0;else if (cur_status == RD_PRE)m_axi_arvalid <= 1'b1;else if (m_axi_arvalid && m_axi_arready)m_axi_arvalid <= 0;
end/*-----------------------------------------------------------*\read user data from data fifo
\*-----------------------------------------------------------*/
always @(posedge axi_clk) begindata_din  <= m_axi_rdata;data_wren <= m_axi_rvalid;
end assign data_rden = reset_sync ? 1'b0 : ~data_rdempty;always @(posedge clk) beginuser_rd_valid  <= data_rden;user_rd_data   <= data_dout;
end//读地址fifo
fifo_w32xd16 rd_cmd_fifo (.rst          ( reset_sync  ), // input wire rst.wr_clk       ( clk         ), // input wire wr_clk         用户写时钟.din          ( cmd_din     ), // input wire [31 : 0] din.wr_en        ( cmd_wren    ), // input wire wr_en.rd_clk       ( axi_clk     ), // input wire rd_clk         从机读时钟 .rd_en        ( cmd_rden    ), // input wire rd_en.dout         ( cmd_dout    ), // output wire [31 : 0] dout.full         ( cmd_wrfull  ), // output wire full.empty        ( cmd_rdempty ), // output wire empty.rd_data_count( cmd_wrcount ), // output wire [4 : 0] rd_data_count.wr_data_count( cmd_rdcount )  // output wire [4 : 0] wr_data_count
);//读数据fifo
fifo_w32xd16 rd_data_fifo (.rst          ( a_reset_sync ), // input wire rst.wr_clk       ( axi_clk      ), // input wire wr_clk        从机写时钟.din          ( data_din     ), // input wire [31 : 0] din.wr_en        ( data_wren    ), // input wire wr_en.rd_clk       ( clk          ), // input wire rd_clk            用户读时钟 .rd_en        ( data_rden    ), // input wire rd_en.dout         ( data_dout    ), // output wire [31 : 0] dout.full         ( data_wrfull  ), // output wire full.empty        ( data_rdempty ), // output wire empty.rd_data_count( data_rdcount ), // output wire [4 : 0] rd_data_count.wr_data_count( data_wrcount )  // output wire [4 : 0] wr_data_count
);
endmodule