The idresadd command first attempts to match the hardware device being added with an existing entry in the Resource Manager. To match, the Resource Manager entry must have no MODNAME set, or a MODNAME that matches the name of the driver being added. Also, the driver must have at least one of its hardware parameters (one of IRQ, DMACHAN, IOADDR, or MEMADDR) set, and the parameter(s) must match in the Resource Manager entry and the System file entry.
If no matching entry is found in the Resource Manager, a new entry is added to the file. No entry is added to the Resource Manager if any entry already exists for a driver unless the -f option is present to force the addition of the entry.
New entries in the Resource Manager database are tagged with CM_ENTRY_DEFAULT, unless -n is given. When -n is given, other entries that match the driver's MODNAME and are tagged with CM_ENTRY_DEFAULT are removed.