sequencer和virtual sequencer的作用

gerry1512

在UVM环境中，一直对sequencer和virtual sequencer的作用没搞明白：
1. driver需要通过sequencer来获取sequence产生的数据，那为什么driver不能直接调sequence呢？我看到平台的sequencer基本都没写多少实际内容，到底有什么必要性？
2. 当有多个sequencer时，需要用到virtual sequencer做路由，这个路由的原理是怎么实现的，virtual的意义在哪里？
希望大佬帮我解答一些，谢谢

vasya

1. Sequence is just a list of transactions (each one is sort of scenario). You can have lots of different sequences, that is lots of scenarios. Sequencer and driver are about TLM (Transaction-level modeling). They use handshake mechanism (Request, Response) to communicate and be synchronized. Someone should support this mechanism, so they are sequencer and driver. The driver can non directly communicate with a sequence class because it does not have Request-Response mechanism.
2. Virtual means no real transaction scenario it have. But it holds other sequences (scenarios) which definitely comprise the scenarios. You can do synchronization between sequences by means of “wait for some action” which goes from the next sequence.

vasya

Check this DVCON paper: "What Does the Sequence Say Powering Productivity with Polymorphism"

seabeam

virtual sequencer或者叫做top sequencer, 其实只是一个容器，把各个physical sequencer或者子virtual sequencer包在一起。

好处是sequencer多的时候不用一个一个传了，而且这个sequencer毕竟是uvm_component，还能用来向seq传递一些TB的资源