Refactor in preparation for the addition of a Rev 3 simulator for the
3B2/1000 system.
This change also includes a full cleanup of the rat's-nest of includes
and externs that plagued the 3B2 simulator and made it difficult to
understand and maintain. Headers are now required in the following
order:
compilation unit -> "3b2_defs.h" -> {... dependencies ...}
Finally, HELP has been added to the CPU device.
- The DMAC controller "Current Word Count" expects to decrement
beyond 0 to 0xffff. Its initial value should also be 0xffff.
Setting the initial value to 0 introduced a very subtle bug
related to DUART self-test following a soft power reset.
This change cleans up warnings issued when compiled with
-Wall.
- Removed unused functions and variables.
- Moved static declarations out of headers and into source files
- Added braces around initialization where suggested.
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.
