84PCE:Ports:5000

This port range has an interesting semi-pattern of read-only and latching ports. Some of these ports have a critical function for interrupt-handling. A partial list is below, but ports with some kind of function continue until at least 5055.

It seems to be arranged in 22-bit bitfields (each occupying a little-endian 32-bit word), with each bit corresponding to a different interrupt source. Known sources so far:

Bit	Interrupt Source
0	ON Button
4	Unknown, but disabling causes freeze (might be OS timer?)
10	Keyboard
11	LCD Controller
15	Unknown, but signal seems to be constantly on

This range is (probably?) memory-mapped to F00000.

Port	Default	Bits	Information
5000	Read-Only	003FFFFF	Raw interrupt status (can be either raw signal or latched on signal change from low-to-high).
5004	00003011	003FFFFF	Interrupt enable mask.
5008	Write-Only	003FFFFF	Interrupt acknowledge (used by ISR), seems to only affect latched status bits.
500C	00000019	003FFFFF	Determines whether bits of 5000 will latch. 0 means raw signal, 1 means latched.
5010	00000000	003FFFFF	Unknown function.
5014	Read-only	003FFFFF	Masked interrupt status (used by ISR). Should be equal to (5000 & 5004).
5018	Read-only	????????	Ports 5018-501F may always read zero
5020			Ports 5020-503F seem to be identical in function to 5000-501F (but not mirrors). These registers do not seem to actually trigger interrupts. Assuming this chip was meant for use with ARM, this would likely have been intended to drive the FIQ signal, but the eZ80 has no such alternative interrupts.