The ROMC bit of D030 enables ROM at $C000. The docs are unclear what this is for and when it can be safely disabled, and is indirect about its function. ROMC is the INTERFACE area and is used for low-level KERNAL operations, and needs to be left enabled (and C000-DFFF un-MAP'd) as a precondition for most KERNAL entry points.
The ROMC bit of D030 enables ROM at $C000. The docs are unclear what this is for and when it can be safely disabled, and is indirect about its function. ROMC is the INTERFACE area and is used for low-level KERNAL operations, and needs to be left enabled (and C000-DFFF un-MAP'd) as a precondition for most KERNAL entry points.