Initial commit of XENTRAL
Implement push/pop.

Add logic to do inplace register increment/decrement.
Add that logic to the SP register.
Add control logic for push/pop instructions.
Add an additional path that enables us to load a value from bus3 into the control unit.
Implement CALL/RET
Never output 'Z'. It confuses STA/ISIM.

Re-engineered the bus drivers so that they never output 'Z'.
This is achieved by switching signals instead of relying on explicit tri-states.
Actually add the DRIVESEL source

(Oops)
Add license

Added a license file.
The project is now under CC-by-NC. Contact author to negotiate different terms.
Bring some sanity to the names

DEMUX16 is not DECODE16
IIR is now IR
IR is now CONTR
Change tabs to spaces

Change tabs to spaces to make formatting less editor-dependent
Reorganize main module layout

Reorganize main module layout so it's in a more logical order
Support additional indexing modes in ISA

Alter the ISA to include double-ALU indexing modes for load and store operations.
Move HDL files into a folder.

Move HDL files into a folder so we can add other things to the project, such as docs and tools.
Add basic assembler

Add an basic one-pass assembler
Make immediate jumps relative
Backed out changeset: 5ddda2adacd8

We'll try something else instead
Immediate jumps are within the PC's high-nibble.

Implement MIPS-style absolute jumps, leaving the PC's high nibble intact.
Wire unused ALU flag to ground.

Wire unused ALU flag to ground to avoid dealing with undefined signals.
Add indirect jumps, rejiggle branches

Add indirect jumps.
Move branches under their own sub-instruction (0xD)
Update assembler to output VHDL

Enable the assembler to output VHDL
Add the new-style branch instructions
Add a fibonacci example.
Fix branch instructions

Delay branch instruction by one cycle to allow the execution unit to catch up.
Encode SP

Add SP as a special case to the list of registers to encode.