LUN_FUNCTIONS Structure

typedef struct {
  BYTE (* MediaInitialize)();
  DWORD (* ReadCapacity)();
  WORD (* ReadSectorSize)();
  BYTE (* MediaDetect)();
  BYTE (* SectorRead)(DWORD sector_addr, BYTE* buffer);
  BYTE (* WriteProtectState)();
  BYTE (* SectorWrite)(DWORD sector_addr, BYTE* buffer, BYTE allowWriteToZero);
} LUN_FUNCTIONS;

LUN_FUNCTIONS is a structure of function pointers that tells the stack where to find each of the physical layer functions it is looking for. This structure needs to be defined for any project for PIC24F or PIC32. 

Typical Usage:

    LUN_FUNCTIONS LUN[MAX_LUN + 1] =
    {
        {
            &MDD_SDSPI_MediaInitialize,
            &MDD_SDSPI_ReadCapacity,
            &MDD_SDSPI_ReadSectorSize,
            &MDD_SDSPI_MediaDetect,
            &MDD_SDSPI_SectorRead,
            &MDD_SDSPI_WriteProtectState,
            &MDD_SDSPI_SectorWrite
        }
    };

In the above code we are passing the address of the SDSPI functions to the corresponding member of the LUN_FUNCTIONS structure. In the above case we have created an array of LUN_FUNCTIONS structures so that it is possible to have multiple physical layers by merely increasing the MAX_LUN variable and by adding one more set of entries in the array. Please take caution to insure that each function is in the the correct location in the structure. Incorrect alignment will cause the USB stack to call the incorrect function for a given command. 

See the MDD File System Library for additional information about the available physical media, their requirements, and how to use their associated functions.