Disc operations


devctl(DC_DISC_CHECK, Unit)

   returns the number of blocks on disc drive Unit (1 to 8)
   returns 0 if the indicated disc is not available
   or -2 if the parameter could not be read
   or -3 if the unit number is not in range 1 to 8


devctl(DC_DISC_READ, Unit, FirstBlock, NumberOfBlocks, MemAddress)

   reads the indicated blocks into memory starting at MemAddress.
   MemAddress must point to at least NumberOfBlocks*128 words of memory.
   returns number of blocks actually read
   or -2 if the parameters could not be read
   or -3 if the unit number is not available
   or -4 if a block number is out of range
   or -5 if MemAddress could not be read from


devctl(DC_DISC_WRITE, Unit, FirstBlock, NumberOfBlocks, MemAddress)

   writes the indicated blocks from memory starting at MemAddress.
   MemAddress must point to at least NumberOfBlocks*128 words of memory.
   returns number of blocks actually written
   or -2 if the parameters could not be read
   or -3 if the unit number is not available
   or -4 if a block number is out of range
   or -5 if MemAddress could not be written to
   or -6 if it could not write all of the data to disc