chi协议简单总结

1. 三个层次对应的职责；

协议层

负责产生和处理请求与响应；

负责维护cache state；

负责处理整个protocal level flow;

网络层

对协议层的message进行封装；

产生srcid/tgtid, 用于message在网络中进行传输；

链路层

device间，flow control;

负责各个通道间的建链解链；

2. Topology的分类与区别；

crossbar	低延时，适用于小规模nodes;
ring	效率与延时平衡，适用于中等规模nodes;
mesh	高带宽，可扩展性更强，适用于大规模nodes;

3. 常用术语：

transaction	一笔读写操作
message	两个component之间的传输，例如，一笔request, 一笔response, 一笔snoop等等；
packet	一笔message的多个packet，例如，一个data_resp,可能分多次传输回来；
flit	在chi中，一个packed=一个flit;
pos	保序点
poc	一致性点，
	A point at which all agents that can access memory are guaranteed to see the same copy of a memory location. In a typical CHI based system it is the HN-F in the interconnect.
requester	A component that starts a transaction by issuing a Request message.
Completer	Any component that responds to a transaction it receives from another component.
	可以是interconnect上的一个组件，也可以是之外的一个组件（slv）
Master	An agent that independently issues transactions
	A master can also be referred to as a Requester
	Typically a master is the most upstream agent in a system
Slave	An agent that receives transactions and completes them appropriately
	A slave can also be referred to as a Completer or Endpoint.
	Typically, a slave is the most downstream agent in a system
Protocol Credit	A credit, or guarantee, from a Completer that it will accept a transaction.
Link layer Credit	A credit, or guarantee, that a flit will be accepted on the other side of the link
ICN	An ICN might include a fabric of switches connected in a ring, mesh, crossbar, or some other topology
IPA	Intermediate Physical Address
RN	Request Node. Generates protocol transactions, including reads and writes, to the interconnect.
	RN-F
	Fully coherent Request Node
	• Includes a hardware-coherent cache.
	• Permitted to generate all transactions defined by the protocol.
	• Supports all Snoop transactions.
	RN-D
	IO coherent Request Node with DVM support:
	• Does not include a hardware-coherent cache. • Receives DVM transactions. • Generates a subset of transactions defined by the protocol.
	RN-I
	IO coherent Request Node
	• Does not include a hardware-coherent cache.
	• Does not receive DVM transactions.
	• Generates a subset of transactions defined by the protocol.
	• Does not require snoop functionality.
HN	Home Node. Node located within the interconnect that receives protocol transactions from Request Nodes, completes the required Coherency action, and returns a Response.
	HN-F
	Is expected to receive all Request types except DVMOp
	• Includes a Point of Coherence (PoC) that manages coherency by snooping the required RN-Fs, consolidating the snoop responses for a transaction, and sending a single response to the requesting RN.
	• Is expected to be the Point of Serialization (PoS) that manages order between memory requests.
	• Might include a directory or snoop filter to reduce redundant snoops.
	HN-I
	Processes a limited subset of Request types defined by the protocol
	• Is expected to be the PoS which manages order for requests targeting the IO subsystem.
	• Does not include a PoC and is not capable of processing a Snoopable request. On receipt of a Snoopable request must respond with a protocol compliant message.
	MN
	Miscellaneous Node:
	• Receives a DVM transaction from an RN, completes the required action, and returns a response
SN	Slave Node. Node that receives a Request from a Home Node, completes the required action, and returns a Response
	SN-F
	A Slave Node type used for Normal memory.
	It can process Non-snoopable read write, and atomic requests, including exclusive variants of them, and Cache Maintenance Operation (CMO) requests
	SN-I
	A Slave Node type used for peripherals or Normal memory.
	It can process Non-snoopable read, write and atomic requests, including exclusive variants of them, and CMO requests.
MN	Misc or Miscellaneous Node. Node located within the interconnect that receives DVM messages from Request Nodes, completes the required action, and returns a Response
IO Coherent node	The Snoopable requests that an IO Coherent node generates do not result in the caching of the received data in a coherent state. Therefore, an IO Coherent node does not receive any Snoop requests
Write-Invalidate protocol	A protocol in which an RN writing to a cache line that is shared in the system must invalidate all the shared copies before proceeding with the write. The CHI protocol is a Write-Invalidate protocol.
In a timely manner	The protocol cannot define an absolute time within which something must occur. However, in a sufficiently idle system, it will make progress and complete without requiring any explicit action
Don’t Care	Any component receiving a packet with a field value set to Don't Care must ignore the value set for that field
Inapplicable	A field value that indicates that the field is not used in the processing of the message