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*  GRU ocpu - yet another cpu design
** Features
   - little endian
   - 16-bit
** Registers
   
   |----------+----------+-------------------------|
   | Register | Category | Description             |
   |----------+----------+-------------------------|
   | AL       | General  | 0xA0, 8-bit             |
   |----------+----------+-------------------------|
   | AH       | General  | 0xA1, 8-bit             |
   |----------+----------+-------------------------|
   | A        | General  | 0xAA, 16-bit            |
   |----------+----------+-------------------------|
   | BL       | General  | 0xB0, 8-bit             |
   |----------+----------+-------------------------|
   | BH       | General  | 0xB1, 8-bit             |
   |----------+----------+-------------------------|
   | B        | General  | 0xBB, 16-bit            |
   |----------+----------+-------------------------|
   | CL       | General  | 0xC0, 8-bit             |
   |----------+----------+-------------------------|
   | CH       | General  | 0xC1, 8-bit             |
   |----------+----------+-------------------------|
   | C        | General  | 0xCC, 16-bit            |
   |----------+----------+-------------------------|
   | DL       |          | 0xD0, 8-bit 4           |
   |----------+----------+-------------------------|
   | DH       |          | 0xD1, 8-bit             |
   |----------+----------+-------------------------|
   | D        |          | 0xDD, 16-bit            |
   |----------+----------+-------------------------|
   | EL       |          | 0xE0, 8-bit             |
   |----------+----------+-------------------------|
   | EH       |          | 0xE1, 8-bit             |
   |----------+----------+-------------------------|
   | E        |          | 0xEE, 16-bit            |
   |----------+----------+-------------------------|
   | FL       |          | 0xF0, 8-bit             |
   |----------+----------+-------------------------|
   | FH       |          | 0xF1, 8-bit             |
   |----------+----------+-------------------------|
   | F        |          | 0xFF, 16-bit            |
   |----------+----------+-------------------------|
   | PC       | Pointer  | Program Counter, 16-bit |
   |----------+----------+-------------------------|
   | SP       | Poiner   | Stack Pointer, 16-bit   |
   |----------+----------+-------------------------|
   | ZF       | Flag     | Zero Flag               |
   |----------+----------+-------------------------|
   | NF       | Flag     | Negative Flag           |
   |----------+----------+-------------------------|
   | CF       | Flag     | Carry Flag              |
   |          |          |                         |
   |----------+----------+-------------------------|
   | OF       | Flag     | Overflow Flag           |

** Instuctions
   
   |--------------+--------+-------------------------------------------|
   | Instructions | Opcode | Description                               |
   |--------------+--------+-------------------------------------------|
   | MOV          |   0x01 | Place value to register.                  |
   |              |        | Takes 2 bytes as arguments:               |
   |              |        | 1 - Opcode of register                    |
   |              |        | 2 - Value                                 |
   |              |        |                                           |
   |--------------+--------+-------------------------------------------|
   | ADD          |   0x10 |                                           |
   |--------------+--------+-------------------------------------------|
   | ADC          |   0x11 |                                           |
   |--------------+--------+-------------------------------------------|
   | SUB          |   0x12 |                                           |
   |--------------+--------+-------------------------------------------|
   | MUL          |   0x13 |                                           |
   |--------------+--------+-------------------------------------------|
   | DIV          |   0x14 |                                           |
   |--------------+--------+-------------------------------------------|
   | INC          |   0x15 | Increment                                 |
   |--------------+--------+-------------------------------------------|
   | DEC          |   0x16 | Decrement                                 |
   |--------------+--------+-------------------------------------------|
   | AND          |   0x20 |                                           |
   |--------------+--------+-------------------------------------------|
   | OR           |   0x21 |                                           |
   |--------------+--------+-------------------------------------------|
   | NOR          |   0x22 |                                           |
   |--------------+--------+-------------------------------------------|
   | XOR          |   0x23 |                                           |
   |--------------+--------+-------------------------------------------|
   | NAND         |   0x24 |                                           |
   |--------------+--------+-------------------------------------------|
   | CMP          |   0x25 | Compare                                   |
   |--------------+--------+-------------------------------------------|
   | PUSH         |   0x30 | Push to stack                             |
   |--------------+--------+-------------------------------------------|
   | POP          |   0x31 | Pop to stack                              |
   |--------------+--------+-------------------------------------------|
   | JMP          |   0x40 | Jump                                      |
   |--------------+--------+-------------------------------------------|
   | JSR          |   0x41 | Jump to subroutine                        |
   |--------------+--------+-------------------------------------------|
   | JC           |   0x42 | Jump with carry                           |
   |--------------+--------+-------------------------------------------|
   | JNC          |   0x43 | Jump without carry                        |
   |--------------+--------+-------------------------------------------|
   | JZ           |   0x44 | Jump if zero                              |
   |--------------+--------+-------------------------------------------|
   | JNZ          |   0x45 | Jump if non-zero                          |
   |--------------+--------+-------------------------------------------|
   | JE           |   0x46 | Jump if equal                             |
   |--------------+--------+-------------------------------------------|
   | JL           |   0x47 | Jump if lower                             |
   |--------------+--------+-------------------------------------------|
   | JH           |   0x48 | Jump if higher                            |
   |--------------+--------+-------------------------------------------|
   | RTS          |   0x49 | Return from subroutine                    |
   |--------------+--------+-------------------------------------------|
   | INB          |   0x50 | Copies value from I/O port to destination |
   |--------------+--------+-------------------------------------------|
   | OUTB         |   0x51 | Copies value from operand to I/O port     |
   |--------------+--------+-------------------------------------------|
   | NOP          |   0x90 | No operation                              |


0x0* - MOV instructions (maybe it will for LDA or something)

0x1* - Arithmetic (ADD, SUB and others)

0x2* - Logic (AND, OR and others)

0x3* - Stack Operations (PUSH, POP)

0x4* - Jumps

0x5* - Ports Operations

0x90 - NOP


TODO: add interrupts

TODO: add HLT

TODO: make instructions for memory use

TODO: add instructions for setting flags

TODO: add more description

TODO: add ALU