AMBA CHI协议学习笔记5-Exlusive、Stashing、DVM

【本系列文章是我自己对CHI协议的学习笔记，仅供参考，欢迎指正。】

【文中的红色字体是我自己的标注，本文参考了 谷公子 作品，特此鸣谢】

一、exlusive

1、Snoopable memory location

LP monitor：RN-F内的每个LP都必须实现一个exclusive monitor，用于检查exclusive sequence访问使用的地址信息。LP在执行Exclusive Load时，LP monitor置位；LP monitor在收到同地址的invalidating snoop request或同一个LP对该地址产生的non-exclusive store复位。

PoC monitor：HN-F必须实现一个PoC monitor，用于判定Exclusive Store transaction的结果是成功还是失败。如果HN可以判定RN已有copy，那么PoC monitor可以不用。如果是S态的copy，会先把它整成U态的，然后再store。

由于monitor的最小单位是传输事务size，最大是64B，故可能把成功的exclusive访问误判为失败（相邻地址的数据被snoop了）。所以：The PoC monitor can be enhanced to include some address comparison.

An Exclusive Store transaction is permitted to progress if one of the following occurs:
• The address monitor has registered an exclusive sequence for a matching address from the same LP and has not been reset by an Exclusive Store transaction from a different LP with a matching address.
• The minimum single-bit monitor has been set by an exclusive sequence from the same LP, and it has not been reset by an Exclusive Store transaction from a different LP to any address.

2、Non-snoopable memory location

System monitor：系统monitor会跟踪访问Non-snoopable地址空间的Exclusive访问。该monitor在有ReadNoSnp(Excl)操作时置位，会被其它同地址LP的改写而复位。

 3、ReadPreferUnique and MakeReadUnique do not use RespErr to determine the pass or fail of an Exclusive operation. An Exclusive MakeReadUnique response with Shared cache state indicates the failure of an Exclusive access. When the response cache state is Unique, the Requester must use its Local Monitor state to determine if the Exclusive access is a pass.

这里为什么获得了unique还需要检查LP monitor呢？因为unique可能是别的事务的结果。

4、适用于exclusive的事务

Exclusive Load transaction to a Snoopable location:
— ReadClean
— ReadNotSharedDirty
— ReadShared
— ReadPreferUnique
• Exclusive Store transaction to a Snoopable location:
— CleanUnique
— MakeReadUnique
• Exclusive Load transaction

5、其他：

这里是因为DMT和DCT无法monitor啊

二、stashing

就是建议某个RN去get一个cache，注意这是个hint，不是必须办。

1、Write with Stash hint

待补充内容

2、Independent Stash request

待补充内容

三、DVMop

1、DVMop的典型场景