# TyVM - [T]in[y] [V]irtual [M]achine
TyVM is a 16bit VM based on the LC-3 architechture that runs Assembly code, and could more generally run even an operating system

## Resources
https://en.wikipedia.org/wiki/Little_Computer_3

### Build
On file "preprocessor.c" define the OS where you want to run TYVM:

  #define __UNIX

Uncomment this line if you want to build for Unix based OS, otherwise comment it out to build for Windows
Build using the command:
``` 
gcc tyvm.c -o tyvm
```
Or simply using makefile (optional: in makefile change binary file name wether building on Unix or Windows):

``` 
make
```

### Hardware
TYVM is a very barebone 16-bit system on LC-3 architechture. It has:
  - 128kb memory (65,536 memory locations)
  - 10 registers:
  - 3 condition flags

#### Memory
It has 2^16(=65,536) individual memory locations
```
uint16_t memory[UINT16_MAX];
```
#### Registers
TYVM has n.10 16-bit registers.
    - 8 general purpose registers
    - 1 program counter (PC)
    - 1 conditional register (COND)

```c
enum {
    RG_000 = 0,
    RG_001,
    RG_010,
    RG_011,
    RG_100,
    RG_101,
    RG_110,
    RG_111,
    RG_PC,
    RG_COND,
    RG_COUNT
};
uint16_t registers[R_COUNT];
```
#### Instruction set
TYVM has n.16 16-bit opcodes, that instructs the machine to do some simple calculation:
```c
enum {           // [name, 8-bit value]
    OP_BR = 0,      // branch, 0000
    OP_ADD,         // add, 0001
    OP_LD,          // load, 0010
    OP_ST,          // store, 0011
    OP_JSR,         // jump register, 0100
    OP_AND,         // bitwise and, 0101
    OP_LDR,         // load register, 0110
    OP_STR,         // store register, 0111
    OP_RTI,         // unused opcode
    OP_NOT,         // bitwise not, 1001
    OP_LDI,         // indirect load, 1010
    OP_STI,         // indirect store, 1011
    OP_JMP,         // jump, 1100
    OP_RES,         // reserved opcode,
    OP_LEA,         // load effective address, 1110
    OP_TRAP,        // execute trap, 1111
};
```

### Logic
10  Load instruction from memory at program counter [RG_PC] address;
20  Increment RG_PC;
30  Read opcode for next instruction;
40  Perform instruction read in 40;
50  Goto 10;

### Usage
```bash
./tyvm <*.asm>
```

Below is a `hello-word` program for `TYVM`, the assembled program can be found in `asm` directory
```shell
.ORIG x3000
LEA R0, HENLO_WORLD
PUTS
HALT
HELLO_STR .STRINGZ "Henlo World!"
.END
```