Method: CHD::CD#read_sector

Defined in:
lib/chd/cd.rb

#read_sector(lbasector, datatype = nil, phys = false) ⇒ String

Read one or more sectors from a CD-ROM

Parameters:

  • lbasector (Integer) —

    sector number

  • datatype (Symbol) (defaults to: nil) —

    type of data

Returns:

  • (String) 


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# File 'lib/chd/cd.rb', line 151

def read_sector(lbasector, datatype = nil, phys = false)
    # Compute CHD sector and track index
    frame_ofs_type = phys ? :physframeofs : :logframeofs
    chdsector      = lbasector
    trackidx       = 0
    @mapping.each_cons(2).with_index do |(cur, nxt), idx|
        if lbasector < nxt[frame_ofs_type]
            chdsector = lbasector - cur[frame_ofs_type] + cur[:chdframeofs]
            trackidx = idx
            break
        end
    end


    trackinfo = @toc[trackidx];
  tracktype = trackinfo[:trktype]

  offset, length, header =
         # return same type or don't care
         if (datatype == tracktype) || datatype.nil?
             [ 0,  trackinfo[:datasize] ]
             
  # return 2048 bytes of MODE1 data
         #   from a 2352 byte MODE1 RAW sector
  elsif (datatype  == :MODE1    ) &&
               (tracktype == :MODE1_RAW)
      [ 16, 2048 ]
             
  # return 2352 byte MODE1 RAW sector
         #  from 2048 bytes of MODE1 data
  elsif (datatype  == :MODE1_RAW) &&
               (tracktype == :MODE1    )
      warn "promotion of MODE1/FORM1 sector to MODE1 RAW is incomplete"
             m, sf = lba.divmod(60 * 75);
             s, f  = sf.divmod(75)
             hdr   = SYNCBYTES + [
          ((m / 10) << 4) | ((m % 10) << 0), # M
          ((s / 10) << 4) | ((s % 10) << 0), # S
          ((f / 10) << 4) | ((f % 10) << 0), # F
                 1                                  # MODE1
             ].pack('C*') # MSF + MODE1
             
             [ 0, 2048, hdr ]
             
  # return 2048 bytes of MODE1 data
         #   from a MODE2 FORM1 or RAW sector
         elsif (datatype  == :MODE1      ) &&
              ((tracktype == :MODE2_FORM1) || (tracktype == :MODE2_RAW  ))
      [ 24, 2048 ]
             
  # return 2048 bytes of MODE1 data
         #   from a MODE2 FORM2 or XA sector
  elsif (datatype  == :MODE1         ) &&
               (tracktype == :MODE2_FORM_MIX)
      [  8, 2048 ]
             
         # return MODE2 2336 byte data
         #   from a 2352 byte MODE1 or MODE2 RAW sector (skip the header)
  elsif (datatype  == :MODE2) &&
              ((tracktype == :MODE1_RAW) || (tracktype == :MODE2_RAW))
      [ 16, 2336 ]
             
         # Not supported
         else
             raise NotSupported,
                   "conversion from type %s to type %s not supported" % [
                       tracktype, datatype ]
  end

    # Read data
  unless phys 
 if ! trackinfo[:pgdatasize].zero?
    # chdman (phys=true) relies on chdframeofs to point
            # to index 0 instead of index 1 for extractcd.
    # Actually playing CDs requires it to point
            # to index 1 instead of index 0,
            # so adjust the offset when phys=false.
    chdsector += trackinfo[:pregap]
        elsif  lbasector < trackinfo[:logframeofs]
     # if this is pregap info that isn't actually in the file,
            # just return blank data
            return '\0' * length
 end
  end

    data = @chd.read_bytes(chdsector * FRAME_SIZE + offset, length)
    data = header + data if header
    data
end