1. WHAT IS AXI?
AXI是一种高级可扩展接口，是ARM AMBA的一部分。
2. WHAT IS AMBA?
AMBA是高级微控制器总线架构，开放的片内互联总线标准。
3．AXI分类
AXI4/AXI4_ITE/AXI4_STREAM
Memory_mapped 存储器映射 就是读写数据时需要目标地址。
AXI4(AXI4_FULL):用于高性能存储映射。例如：AXI4读写DDR3。
AXI4_LITE:简单的，低吞吐率。比如说一些控制寄存器和状态寄存器。
AXI4_STREAM（ST）：高速的流数据通信。
AXI4(AXI4_FULL)和AXI4_LITE需要主机指定读写的地址。AXI4_STREAM（ST）属于流数据，不需要存储器映射不需要地址。
4.存储器映射（Memory_mapped）
主机在对从机进行读写操作时，要先指定一个目标地址（target address），在这个地址对应系统存储空间的地址，表示对该空间进行读写操作。
Memory-Mapped Protocols: In memory-mapped protocols (AXI3, AXI4, and
AXI4-Lite), all transactions involve the concept of transferring a target
address within a
system memory space and data.
AXI_Stream不属于存储器映射。
5.AXI4的优势
AXI的优势
生产力：
灵活性：AXI4（支持突发256）和AXI4_lite（不支持突发，1个数据）都属于存储器映射。AXI_ST不属于存储器映射，突发长度不受限制。
可获得性：
6.what is 互联？
7. five different channels
Both AXI4 and AXI4-Lite interfaces consist of five different channels:
• Read Address Channel
• Write Address Channel
• Read Data Channel
• Write Data Channel
• Write Response Channel
主机发送读地址，从机返回读数据
Data can move in both directions between
the master and slave simultaneously, and data
transfer sizes can vary. The limit in AXI4 is a burst
transaction of up to 256 data transfers.
AXI4-Lite allows only one data transfer per
transaction.
读操作：主机通过读地址通道向从机发出地址和控制，从机通过读数据通道发送读数据。根据突发长度大小返回不同个数的数据。
写操作：主机先通过写地址通道发出地址和控制信号。然后通过写数据通道发出数据，等从机接收到数据会发送response信号。
AXI4:
读写地址分离，支持同时读写。
需要一个单一地址然后进行256个数据突发。
As shown in the preceding figures, AXI4:
• Provides separate data and address connections for
reads and writes, which allows
simultaneous, bidirectional data transfer.
• Requires a single address and then bursts up to 256
words of data.
AXI4_LITE:
单次一个数据，不支持突发传输。
AXI4-Lite is similar to AXI4 with some
exceptions: The most notable exception is that
bursting is not supported.
AXI4-Stream：
单通道传输数据类似AXI4的写数据通道，且写数据大小没有突发限制。
The AXI4-Stream protocol defines a single channel for
transmission of streaming data. The AXI4-Stream channel models the write data channel of AXI4.
Unlike AXI4, AXI4-Stream
interfaces can burst an unlimited amount of data.
只关心数据流，不需要地址。
AXI4-Stream
Protocol: Use the AXI4-Stream protocol for applications that typically
focus on a data-centric and data-flow paradigm where the concept of an address
is not
present or not required. Each AXI4-Stream acts as a single unidirectional
channel with a
handshaking data flow.