Function Table Header

The structure of the function table header is described below.

        typedef struct 
        {  
        unsigned char  FTH_Num;      /* Class number */ 
        unsigned char  FTH_StartAbs; /* Constant start position */ 
        void far *     FTH_NextTbl;  /* far pointer to next table */ 
        unsigned int   FTH_CS;       /* code segment of functions in table*/ 
        unsigned char  FTH_RamPg;    /* ram page */ 
        unsigned char  FTH_RomPg;    /* rom page */ 
        unsigned char  FTH_RomDev;   /* rom device id */ 
        unsigned char  FTH_Pages;    /* pages to map */ 
        unsigned char  FTH_Start;    /* first function number in table*/ 
        unsigned char  FTH_End;      /* last function number in table*/ 
        } FNCTTBLHEADER; 

• FTH_Num

  Identifies the class to which this function table belongs. The System Manager doesn't currently use this field, since the Class number is passed to the functions that require it.

• FTH_StartAbs

  This field holds the FTH_Start value when a function table is disabled and a value of 255 is placed in the FTH_Start field. FTH_StartAbs need not be initialized to any value when inserting a function table.

• FTH_NextTbl

  In the event of a class having multiple function tables, the next function table is accessed using FTH_NextTbl, a far pointer to the next function table. A value of 0 here indicates no more function tables.

• FTH_CS

  All functions accessed by a function table need to be in the same code segment. The common CS value is stored here.

  Note that the CS is common only for a function table. Multiple Function tables for the same class may have the functions in separate segments.

• FTH_RamPg

  This field gives the page in RAM where the code needs to be bank-switched in. If the sign bit is set, it signals that no bank switching is required.

• FTH_RomPg

  Gives the page in ROM where the code needs to be bank-switched in from. This field is ignored if bank switching is not required.

• FTH_RomDev

  The device from which bank switching is performed. This field is ignored if bank switching is not required.

• FTH_Pages

  This field defines the number of pages that need to be bank-switched. FTH_RomDev is ignored if bank-switching is not required.

• FTH_Start

  Gives the number of the first function available in the function table.

  Note that function number 0 is reserved as the class identifying function. Function number 255 is reserved to indicate a disabled function table, and should not be used. These restrictions allow a maximum of 254 (1 to 254) usable functions per class.

• FTH_End

  Gives the number of the last function available in the function table.