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RCOS C++ CRC for class XfReq

Name:

 XfReq

Comment:

 A "Transfer Request" class; being an object created for each quantum of disk activity. It gets posted to the appropriate drive unit and enters its FIFO queue. When actioned, the CpmBdos pointer is used to call the member function that knows (via a constant placed in the object by the previous member function) which member function to pass the object along to next.

Normally, the pointer will be a copy of the buffer address in the FCB, but making it separate allows the BDOS to present the disk driver with the address of its internal buffers without danger of the user code accidentally gaining access to them.

Note: stuff which class is not concerned with is hidden away - including C::tor and D::tor.

Collaborators:

Responsibilities:

  class XfReq {
    friend CpmFs;
    friend CpmBdos;
  protected:
    PFCB   pFcb;                // instance of an FCB in the PCB or BDOS
    NXTFNC ivec;                // what to do next (internal to CpmBdos)
    BYTE   nRetry;              // error retry count
    XfReq *pNxt;                // any "postponed" assosociated Xfer
   ~XfReq (void) { }            // only friends can destroy
    XfReq (UINT16 = 0);         //    or create one of these..
    XfReq (UINT16, PFCB);
  public:
    UINT16   uProc;             // transfer initiator PID (or BDOS ID)
    CHCMD    cmnd;              // What we want the disk channel to do
    UINT16   nTrk, nSec, nSid;  // Cylinder, sector, head
    char    *pDma;              // transfer buffer pointer
    BOOL     bRes;              // Outcome of channel operation
    CpmBdos *pFnCb;             // class that handeles completed xfers
  };