Utility routines: FillMemory

       Name: FillMemory                                              [Show more]
       Type: Subroutine
   Category: Utility routines
    Summary: Fill a block of memory with a specified value
    Context: See this subroutine in context in the source code
 References: This subroutine is called as follows:
             * ClearMemory calls FillMemory


 When called directly, this routine fills a whole page of memory (256 bytes)
 with the value in A.

 It can also be called at an arbitrary entry point to fill a specified number
 of locations, anywhere from 0 to 255 bytes. The entry point is calculated as
 as an offset backwards from the end of the FillMemory32Bytes routine (which
 ends at ClearMemory), such that jumping to this entry point will fill the
 required number of bytes. Each FILL_MEMORY macro call takes up three bytes
 (two bytes for the STA (clearAddress),Y and one for the INY), so the
 calculation is essentially:

   ClearMemory - 1 - (3 * clearBlockSize)

 where clearBlockSize is the size of the block to clear, in bytes. See the
 ClearMemory routine for an example of this calculation in action.


 Arguments:

   clearAddress(1 0)    The base address of the block of memory to fill

   Y                    The index into clearAddress(1 0) from which to fill

   A                    The value to fill


 Returns:

   Y                    The index in Y is updated to point to the byte after the
                        filled block


.FillMemory

 FILL_MEMORY 224        ; Fill 224 bytes at clearAddress(1 0) + Y with A

                        ; Falling through into FillMemory32Bytes to fill another
                        ; 32 bytes, bringing the total to 256