UVM方法学与设计模式_5：命令模式 & UVM Sequence

Posted 2021-04-25 数字芯片实验室

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Part 1. 命令模式代码示例

假设有如上一段第一代版本的代码，run函数用于执行对receiver模块的一系列操作/命令。

随着项目的进展，V1需要做一些改变，新增了命令得到V2的代码版本，如下所示：

class Invoker{public: void run(Receiver *receiver, bool IsCrcEnable, bool IsYuvEnable, bool IsNewCmd0Enable, ..., bool IsNewCmdNEnable) { receiver->TurnOn; if (IsCrcEnable) { receiver->CrcOn; } if (IsYuvEnable) { receiver->YuvOn; } if (IsNewCmd0Enable) { receiver->NewCmd0On; } if (IsNewCmd1Enable) { receiver->NewCmd1On; } if (IsNewCmd2Enable) { receiver->NewCmd2On; } . . . if (IsNewCmdNEnable) { receiver->NewCmdNOn; }
 ...
 if (IsNewCmdNEnable) { receiver->NewCmdNOff; } . . .
 if (IsNewCmd2Enable) { receiver->NewCmd2Off; } if (IsNewCmd1Enable) { receiver->NewCmd1Off; } if (IsNewCmd0Enable) { receiver->NewCmd0Off; } if (IsYuvEnable) { receiver->YuvOff; } if (IsCrcEnable) { receiver->CrcOff; } receiver->TurnOff; }}

更不要说，当我们需要对这些操作/命令进行排队，制定优先级和取消操作了。可想而知我们的代码将会变得十分冗长，并且难以阅读和维护（阅读和维护代码往往占用了我们80%的编程时间）。

命令模式可以非常好的解决这个问题。让我们来试着发现这个模式。

上述代码最大的问题是什么呢？run函数知道的太多了（正如我们在之前几篇文章中所说的一样：））！

事实上run函数只需要进行执行操作，并不需要将具体执行的具体操作hard coding进我们的函数体内。

到这里，仔细的同学估计已经想到了，套用之前几篇文章的套路，还是使用多态来进行代码改造（所以说多态才是OOP的根本，只不过C++和SV的多态都借用了继承的方式而已）。

我们将每一个命令都封装一个个具体的对象，那么就非常容易对这些命令进行使能操作。具体可见如下代码（不要在意具体的细节，这里只是示意代码）：

class Command{public: Command(Receiver *pReceiver): m_pReceiver(pReceiver) {} virtual void excute() = 0;protected: Receiver *m_pReceiver;};
class CrcOnCmd: public Command{public: CrcOnCmd(Receiver *pReceiver): Command(pReceiver) {} virtual void excute(){ m_pReceiver->CrcOn(); }};
class CrcOffCmd: public Command{public: CrcOffCmd(Receiver *pReceiver): Command(pReceiver) {} virtual void excute(){ m_pReceiver->CrcOff(); }};
class TurnOnCmd: public Command{public: TurnOnCmd(Receiver *pReceiver): Command(pReceiver) {} virtual void excute(){ m_pReceiver->TurnOn(); }}
class TurnOffCmd: public Command{public: TurnOffCmd(Receiver *pReceiver): Command(pReceiver) {} virtual void excute(){ m_pReceiver->TurnOff(); }}
class YuvOnCmd: public Command{public: YuvOnCmd(Receiver *pReceiver): Command(pReceiver) {} virtual void excute(){ m_pReceiver->YuvOn(); }}
class YuvOffCmd: public Command{public: YuvOffCmd(Receiver *pReceiver): Command(pReceiver) {} virtual void excute(){ m_pReceiver->YuvOff(); }}
class Receiver{public: virtual void TurnOn() {} virtual void TurnOff() {} virtual void CrcOn() {} virtual void CrcOff() {} virtual void YuvOn() {} virtual void YuvOff() {}}
class Invoker{public: void AddCmd(Command *cmd){ vector.push_back(cmd); } void RemoveCmd(Command *cmd){ auto it = find(m_CommandVector.begin(), m_CommandVector.end(), cmd); if (it != m_CommandVector.end()) m_CommandVector.erase(it); } void Run(){ for (auto &it : m_CommandVector) it->excute(); }private: std::vector<Command*> m_CommandVector;}
int main(){ Invoker *invoker = new invoker(); Receiver *receiver = new Receiver(); CrcOnCmd *crconcmd = new CrcOnCmd(receiver); CrcOffCmd *crcoffcmd = new CrcOffCmd(receiver); TurnOnCmd *turnoncmd = new TurnOnCmd(receiver); TurnOffCmd *turnoffcmd = new TurnOffCmd(receiver); YuvOnCmd *yuvoncmd = new YuvOnCmd(receiver); YuvOffCmd *yuvoncmd = new YuvOffCmd(receiver);
 invoker->AddCmd(crconcmd); invoker->AddCmd(yuvoncmd); invoker->AddCmd(turnoncmd);
 invoker->Run();
 return 0;}