Pascal III: Accessing the extra memory (4 of 5)

• Last Modified: November 30, 1984
• Article: TA44967
• Old Article: 642

        ; At this point, there is an assumption that
        ; 1. move partial page and
        ; 2. Testwrap on source and dest
        ;  have been done so we can move at least 256 bytes without
        ;  thinking about it again.
Partial LDA     Count           ; all done yet?
        BEQ     Return
        LDY     #0              ; now move (low byte of Count)
                                ; # of bytes
$1      LDA     @Source,Y
        STA     @Dest,Y
        INY
        CPY     Count
        BNE     $1
;===============================================================
Return  LDA     SaveSrcBank     ; and go home
        STA     SrcBank
        LDA     SaveDstBank
        STA     DstBank
        PUSH    RetAddr
        RTS
 
Retaddr .WORD
 
        .FUNC   Atsign,1
        ; x := Atsign(Y) causes X to point to Y
        PULL    RetAddr
        PLA
        PLA
        PLA
        PLA
        PUSH    RetAddr
        RTS
 
RetAddr .WORD
Loc     .WORD
        .END
 
================================================================
{$SETC Debug := TRUE}
UNIT StringSpace;
 
INTERFACE
    TYPE
       STRING1   = STRING[1];
       STRING255 = STRING[255];
       STRPTR  = INTEGER;
 
    FUNCTION  InitStringSpace(ColdStart:BOOLEAN): INTEGER;
    PROCEDURE FreeStringSpace;
    FUNCTION  PutString(VAR S:STRING1; VAR WHERE:STRPTR):
                        BOOLEAN;
    PROCEDURE GetString(Who:STRPTR; VAR S:STRING255);
                {S had better be 256 bytes long!}
IMPLEMENTATION
 
   VAR
       SegNum,         {segment number of memory chunk}
       Bank,           {what bank is chunk in}
       Base,           {start of chunk received (byte address)}
       Tos,            {next word to allocate}
                       {(base rel word address)}
       Limit: INTEGER; {last word allocatable}
                       {(base rel word address)}
 
    PROCEDURE Allocate(VAR NumPages,Segnum,Bank,SegBase:
                       INTEGER); EXTERNAL;
     {allocates a chunk of SOS memory:
       Input:
         NumPages: Maximum number of pages to try for.
       Output:
         NumPages: Number of pages actually allocated.
         SegNum:   SOS Segment number (for deallocate)}
       { Bank:     Starting address bank number
         SegBase:  Starting address byte address ($0200..$9E00)}
 
    PROCEDURE DeAllocate(SegNum:INTEGER); EXTERNAL;
 
    PROCEDURE FetchBytes(SrcBank:INTEGER; Source:INTEGER;
                         DstBank:INTEGER; Dest:INTEGER;
                         PageCount:INTEGER; Count:INTEGER
                         ); EXTERNAL;
 
FUNCTION Atsign( VAR x:INTEGER):INTEGER; EXTERNAL;
 
FUNCTION InitStringSpace{(ColdStart:BOOLEAN): INTEGER};
VAR
   NumPages:INTEGER;
   TempBase:INTEGER;
BEGIN
   IF ColdStart THEN BEGIN
      FreeStringSpace;
 
          {$IFC  Debug}
          WRITELN('How many pages to allocate?');
          READLN(NumPages);
          IF NumPages > 512 THEN NumPages := 512;
          {$ELSEC Debug}
          NumPages := 512;
          {$ENDC Debug}
 
          Allocate(NumPages,SegNum,Bank,TempBase);
          Base := TempBase - {$2000}8192;   {shift into}
                                            {extended address}
          Limit := NumPages*128 -32767-1;   {128 = words/page}
 
          {$IFC  Debug}
          WRITELN('Assembly results:');
          WRITELN('Segment ',Segnum,' Allocated ',NumPages,
                  ' pages',' in bank ',Bank,' at real address ',
                  TempBase);
          IF Base MOD 256 <> 0 THEN
            WRITELN(CHR(7),'bad base address');
          {$ENDC Debug}
 
       END;
       Tos := -32767-1;         {compiler doesn't like -32768}
       InitStringSpace := NumPages;
    END;