Unknown interrupt flags

[vbe0201]

The Falcon has a special-purpose register for various flag bits that are used and modified by certain events and instructions. While most of the bits that are actually used and implemented are known, few still aren't.

The bits in question are the ones located at 0x1A-0x1F. It can be observed that 0x1A-0x1C are being modified on interrupt/trap delivery. The former values of these bits are copied to 0x1D-0x1F and later restored by the iret instruction.

Neither the purpose of these bits nor the actual meaning of their values is known, any help would be greatly appreciated before these can be implemented.