DCPU-16 1.1

http://www.reddit.com/r/dcpu16/comments/sqfre/rfe_dcpu16_11/


Swapped the names of "a" and "b" to make it more clear what gets processed first, and to make special opcodes not have only a b value.
Added a very basic interrupt handler
Outlined some hardware detection basics
Made the text 80 characters wide because 80's
Implemented ALL of following:

DCPU-16 Spec Suggestions
=======================

1. Evaluate b before a
----------------------------------------------
This makes instructions that address the stack twice meaningful instead of confusing and useless.

`ADD PEEK, POP` *should* pop the top of the stack and add it to the second entry, but currently the `PEEK` is evaluated before the `POP` occurs.

2. Add [SP+next word] addressing
----------------------------------------------
This makes writing functions that store extra variables or arguments on the stack easier.

POP isn't useful as an a value, and PUSH isn't useful as a b value, so they should be combined into one value, with postincrement and predecrement determined by whether they're in a/b.

3. Make opcodes 5 bits
--------------------------------
A literal a value is not very useful, and having 2x more opcodes is very useful.
bbbbbbaaaaaaoooo
becomes
bbbbbbaaaaaooooo

4. Make literal range include -1.
-----------------------------------
Shift the literal range from [0, 31] to [-1, 30].

Having -1 as a literal lets you useful one-word instructions like:
``` NEG X --> MUL X, -1
NOT X --> XOR X, -1```

5. Rename O register to EX or OV
-------------------------------------
O and 0 are very easy to confuse, other special registers are two characters, and it doesn't always represent overflow.

6. Add signed MUL/DIV instructions
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Signed operations make maneuvers, targeting, and fixed-point trigonometry routines more efficient.

Suggested mnemonics: `MLI`, `DVI`.

7. Add signed right shift (ASR)
-----------------------------------------
Signed operations are useful.

8. Add additional IF instructions
------------------------------------
Supporting all the relations (<, >, <=, >=) will make assembly easier to write and read. Suggested mnemonics and effects:

0x11: IFB a, b - performs next instruction only if (a&b)!=0 (Bit set)
0x12: IFE a, b - performs next instruction only if a==b (Equal)
0x13: IFN a, b - performs next instruction only if a!=b (Not equal)
0x14: IFG a, b - performs next instruction only if a>b (signed) (Greater)
0x15: IFA a, b - performs next instruction only if a>b (unsigned) (Above)
0x16: IFL a, b - performs next instruction only if a<b (signed) (Less)
0x17: IFU a, b - performs next instruction only if a<b (unsigned) (Under)


Appendix A.
===========
1. Fix line drawing characters
------------------------------
As [jecowa noted on reddit](http://www.reddit.com/r/dcpu16/comments/sio8u/dcpu_font_help_what_are_those_first_30ish_glyphs/c4ekx9u), you can't make full boxes with the current line drawing characters.

These 22 glyphs let you draw boxes:

│─└┌┐┘┴├┬┤┼

║═╚╔╗╝╩╠╦╣╬

Suggestions for extra 5 glyphs:

° (Degree) and ♠♥♦♣ (Card suits)

Note that the full block █ with fg color X is equivalent to space with bg X. Replace it with a dithered ▒ half-block.