AXI总线要点

AXI4.0是ARM公司提出的AMBA 3.0协议的升级版，是一种高性能、高带宽、低延迟的片内总线，具有总线的地址/控制和数据通道是分离的；支持不对齐的数据传输；在突发传输中，只需要首地址；同时具有分离读/写数据通道；更加容易进行时序收敛。

5个独立通道

写地址通道（Write address channel，AW）；写数据通道（Write data channel，W）；写响应通道（Write response channel，B）；读地址通道（Read address channel，AR）；读数据通道（Read data channel，R）。每个通道都是一个独立的AXI握手协议。

握手机制

每个通道都有一对VALID/READY信号；发送方用VALID指示什么时候数据或控制信息是有效的；接收方用READY指示可以接收数据或控制信息。传输发生在VALID和READY信号同时为高的时候。各信号之间的关系见下图（左图为读事务，右图为写事务）

VALID与READY之间的时序关系见下图。

 

各通道信号

全局信号

写地址通道信号

写数据通道信号

写响应通道信号

读地址通道信号

读数据通道信号

低功耗接口信号

以下是AXI lite IP核各信号的定义：

module AXI_PWM_v1_0_S00_AXI #
	(
		// Users to add parameters here
 
		// User parameters ends
		// Do not modify the parameters beyond this line
 
		// Width of S_AXI data bus
		parameter integer C_S_AXI_DATA_WIDTH	= 32,
		// Width of S_AXI address bus
		parameter integer C_S_AXI_ADDR_WIDTH	= 4
	)
	(
		// Users to add ports here
        output wire pwm_out,
		// User ports ends
		// Do not modify the ports beyond this line
 
		// Global Clock Signal
		input wire  S_AXI_ACLK,
		// Global Reset Signal. This Signal is Active LOW
		input wire  S_AXI_ARESETN,
		// Write address (issued by master, acceped by Slave)
		input wire [C_S_AXI_ADDR_WIDTH-1 : 0] S_AXI_AWADDR,
		// Write channel 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,
		// Write address valid. This signal indicates that the master 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 data (issued by master, acceped by Slave) 
		input 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 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,
		// Write response. This signal indicates the status
    		// of the write transaction.
		output wire [1 : 0] S_AXI_BRESP,
		// 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 (issued by master, acceped by Slave)
		input wire [C_S_AXI_ADDR_WIDTH-1 : 0] S_AXI_ARADDR,
		// 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,
		// Read 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 data (issued by slave)
		output 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 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
	);