Adds a skeleton framework for CIO ("Common I/O") feature cards. The
first feature card to be implemented will be the "PORTS" serial MUX.
Part of this support involved reworking IRQ handling in the CPU. It
now respects both IRQ Vector and IPL.
This change also removes all 'assert(0)' calls from the simulator and
replaces them with generic "Simulator Error" halts. These should only
happen if there's a genuine logic error lurking somewhere.
This change is a major refactor of how DMA and the DUART interact.
DMA implementation can now be overridden by individual devices that
require DMA. Disk and Floppy both continue to use a generic DMA
implementation, but the DUART code replaces the generic DMA with its
own implementation that correctly rate-limits TX. Among other things,
this allows the simulator to work correctly with real serial
terminals. This functionality has been tested on an AT&T 5620 "Blit"
terminal, which can run the 'layers' windowing software from the
simulator.
This commit adds support for the following emulated hard disks:
HD30 30 MB CDC Wren 94155-36
HD72 73 MB CDC Wren II 94156-86
HD72C 72 MB Fujitsu M2243AS
HD135 161 MB Maxtor XT1190
This commit improves the integrated disk (ID) controller's behavior,
enabling full support for up to two 72MB (emulated WREN II)
integrated winchester disks.
