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RCOS C++ CRC for class DskModel

Name:

 DskModel

Comment:

 This class simulates a disk drive using preset constants, based on the mS granularity system clock ticker, in terms of physical attributes of:

  • Track to track seek time
  • Head settle time
  • Rotational Latency
  • Soft error rate

Channel requests arrive via the usual message service. The model actions these in FIFO, moving the "head" missile to the specified "track", delaying for the head settle period, waiting until the required "sector" "arrives" under the "head", then calling the Read/ Write routine to do the transfer to the specific address. Finally, the CpmBdos::NxtFunc member is called (again via the Object pointer in the message), passing it the transfer request object pointer. A parameter in the object indicates what routine is to precess the completed transfer. If this is the end of the chain for the transfer, the XfReq object is destroyed and the blocked process sent a message to resume, otherwise the params are set for another transfer and the message re-posted to join the FIFO queue again.

This sounds convoluted, but it enables us to implement a BDOS which is re-enterant, since all transfers are encapsulated totally in a XfReq object which rattles around independant of, and inter-leaved with, all other such objects without multi-threading or interrupts.

One of these objects should be instantiated for each drive unit to be modelled, but NOTE that it is important to use the same parameter struct when initialising the corresponding File System object so that it "knows" the size of its "drive".

Collaborators:

Responsibilities:

  class DskModel : public port {
  private:
    ddState stage;              // stage of transfer (see enum type)
    BYTE    nLid;               // logical unit ID (0 = "A:" etc)
    BYTE    nAngleInc;          // rotate degrees per mS
    BYTE    nTrkInc;            // mS per head step
    BYTE    nSettle;            // mS to settle after step
    BYTE    nSecAngle;          // degrees per sector
    UINT16  nCurTrk;            // current head location
    UINT16  nCurAngle;          // current angle of sector index "hole"
    UINT32  nErrRate;           // soft error rate (one every...)
    UINT32  nOpCnt;             // count of operations for error emulation
    UINT32  lLastTime;          // gated clock state memory
    UINT32  lHoldTime;          // state memory for delayed events
    int     fd;                 // handle for host "disk" data file
    BOOL    bOk;                // TRUE if disk is on-line and operational
    UINT16  nBps;               // bytes per sector
    UINT32  nBpt;               // bytes per cylinder
    UINT32  nBpd;               // total bytes on "disk"
    TreqstQ ChanQ;              // FIFO queue of requests for this unit
    BOOL    Read (void);        // read to buffer BLOCK_LEN bytes
    BOOL    Write (void);       // write from buffer BLOCK_LEN bytes
    long    CalcOffset (void);  // get offset for host file transfer
  public: 
    DskModel (UINT16, UINT16, Knl*, char*, DPB&, BYTE);
   ~DskModel (void);
    void Scheduler (void);               // called in "main loop"
    void RxPort (PMSG);                  // incomming message handler
    BOOL IsOnLine (void) { return bOk; } // check on c::tor success
  };