#######################################
#  PS 1 Fill Level - PS_HK
# Indentify start of next read address (either last read or start of PS)
if NCDD0AA9.raw < 1 then
   # This PS has not been read
   #
   if NCDD0AAC.raw < 1 then
        # Nor has it been written to - use the PS start address
        VAR_PS1_ReadPtr :=  NCDD0AA8.raw;
   else
       # There's a valid packet though, use the FVPP
   	VAR_PS1_ReadPtr :=  NCDD0AAC.raw;
   endif;
else
  VAR_PS1_ReadPtr := NCDD0AA9.raw;
endif;
#
# Get write address
VAR_PS1_WritePtr := NCDD0AAB.raw;
#
# Difference between them is the amount of unread data
if VAR_PS1_WritePtr >= VAR_PS1_ReadPtr then
   VAR_PS1_UnreadBytes := VAR_PS1_WritePtr - VAR_PS1_ReadPtr;
else
   VAR_PS1_UnreadBytes := (NCDD0AA7.raw + VAR_PS1_WritePtr) - VAR_PS1_ReadPtr; 
endif;
#
# Return amount of data stored in this packet store
return (VAR_PS1_UnreadBytes);