What value should DMAMask be ?

Read the instructions that came with your computer or disk controller. Can it access all memory on your machine ?

If this doesn't help look at your memory map with ShowConfig. Use the maximum memory address as a starting point and adapt it as follows :-

  1. The DMAMask should start with 1, 3, 7 or F. If not substitute the higher value in the list.
  2. Substitute all other digits with F.
  3. Change the last F to a C.
  4. Use this value.

Please look at the above paragraph. If you use MapROM you should check your value as the address quoted by ShowConfig contains a 7 which should be changed.

The following table gives some examples :-

      Address  |   DMAMask
   ------------+------------
    0x001FFFFF | 0x001FFFFC
    0x005FFFFF | 0x007FFFFC
    0x07FCFFFF | 0x07FFFFFC
    0x07FFFFFF | 0x07FFFFFC

If you add memory to you machine you should review you DMAMask settings BEFORE you install the memory ! Another, poorer, option is to set the DMAMask to 0xFFFFFFFC from the word go. This is option is NOT available if your disk controller needs a specific type of memory. See above.