4re5 Virtual Arch

A complete minimal computer architecture directly on your browser. 🚀

Based on the [nandgame][nandgame.com] computer architecture, it provides a simple assembly language to interact with the system.

How it works.

This code emulates a virtual simple machine by interpreting op codes (cpu binary operations).

These op codes are 16 bits of length and are formatted as follow:

| ci | ret | - | * | - | u | op1 | op0 | zx | sw | a | d | *a | lt | eq | gt |
   ┬     ┬       ┬       ┬     ┬     ┬    ┬    ┬   ┬   ┬    ┬    ┬    ┬    ┬ 
   │     │       │       │     │     │    │    │   │   │    │    ╰────┴────┴─ Jump option flags
   │     │       │       │     │     │    │    │   │   │    ╰─ Output is put into ram pointed by A
   │     │       │       │     │     │    │    │   │   ╰─ Output is put into D register
   │     │       │       │     │     │    │    │   ╰─ Output is put into A register
   │     │       │       │     ╰─────┴────┴────┴─ Logical/Arithmetical operations flags
   │     │       │       ╰─ Logical/Arithmetical operation type flag
   │     │       ╰─ Use *A instead of A in operations
   │     ╰─ Return to last JUMP flag
   ╰─ Operation/Number input flag

📖 Assembly manual

Summary

1. Basics of Asm language
2. Registers
3. Conditions

Basics of Asm language

• Arithmetic Operations
  • Only plus and minus are currently supported by our virtual processor. For example:
  • ✅ A = A + D or D = A - D
  • ❌ A = A * D or D = A / D
• Logical Operations
  • Only and, or not and xor can be used for logical operations. For example:
  • A = A & B or D = A | D or A = ~A or D = A ^ B

Warning

Most of unavailable operations could be achieved using our standard library functions

• Register definition

  • Only A register can be directly set to a number < 2^15 since op codes are 16 bits long
  • A represents a pointer that points to the value in memory accessible by *A.

• Mapped memory

NAME	MEMORY AREA	ACCESS MODE	DESCRIPTION
COLOR_FG	RAMSIZE - 14	RW	Foreground Color of the text written using WRITE
COLOR_BG	RAMSIZE - 13	RW	Background Color of the text written using WRITE
STACK_PUSH	RAMSIZE - 12	W	Push a value to the general purpose stack
STACK_POP	RAMSIZE - 11	R	Pop the top value from the general purpose stack
TMP0	RAMSIZE - 10	RW	Temporary memory cell to store function arguments...
TMP1	RAMSIZE - 9	RW	...
TMP2	RAMSIZE - 8	RW	...
TMP3	RAMSIZE - 7	RW	...
TMP4	RAMSIZE - 6	RW	...
TMP5	RAMSIZE - 5	RW	...
TMP6	RAMSIZE - 4	RW	...
CURSOR	RAMSIZE - 3	RW	Cursor position on the virtual terminal
WRITE	RAMSIZE - 2	W	Write a character to the screen at CURSOR position
KEYPRESS	RAMSIZE	R	Read keyboard input

Registers

Operations can be processed using 3 main registers: A, D and *A (which is used as a pointer for ram access)

A is the main one; it is the only one that can be defined directly.

e.g A = 1234 sets the value 1234 into the A register

Others registers can be copied using e.g D = A

*A is a special register. It is a pointer to computer memory. For example

A = 1000
*A = 1    # value to write at offset 1000

Or

A = 1000
D = *A   # reads the memory at offset 1000

This also works using static variables/mapping definitions. e.g.

TEXT:
    i 0     # static variable definition

MAIN:
    A = i   # i is the address of the memory where it has been stored
    *A = 0  # i = 0

    # or
    A = CURSOR # address of the memory mapped byte containing the cursor position
    *A = 0

Conditions

Any condition can be placed after an operation using the ; character.

Warning

NOTE: conditial jumps are conditioned by the sign of the operation before the ; character

Conditions are available to do jumps in your code.

It only exists 7 ones.

• JMP (jump in any case)
• JNE (jump if result != 0)
• JLT (jump if result < 0)
• JLE (jump if result <= 0)
• JEQ (jump if result == 0)
• JGT (jump if result > 0)
• JGE (jump if result >= 0)

Any triggered jump will set the program counter (pc) to the value of the A register.

e.g

A = 15
A; JMP # will jump to line `15`.

After a jump, the current line is pushed into the stack. You can then use RET to return to the parent function at the line of the jump.

e.g

MAIN:
    A = FUNC1
    A; JMP
    # ...

FUNC1:
    ; RET # will go back to the line after the JMP 

Warning

All functions MUST end with 0; RET so the stack remain empty after all jumps or at least do a CLEANING FUNCTION Note that ; RET gets you back to the caller line but 0; RET continues the execution.

📖 C manual

Summary

1. Builtin Functions

Builtin Functions

virtualArch C compiler can handle several builtin functions. Here are the full list with examples.

• write_char(char c)
  • writes a character (here c) to the termial at cursor position defined
  • e.g. write_char('A'); will write the character 'A' to screen
• set_cursor(int pos)
  • sets the screen cursor position to the value of pos
  • e.g. set_cursor(5); will set the cursor to position 5

TODO list

• Add memory mapping for a simple graphic interface
• Add memory mapping for keyboard input
• Add other periferals like sound card and mouse
• Make the js code a whole package
• Create a simple game on this architecture
• Handle if user does not have javascript allowed
• Add exemples
• Enhance the display
• Make the emulator faster and the UI responsive

Asm Language improvements

• Add DEFINE for preprocessing data
• Handle chars when defining A register
• Add labels for better jumps
• Add a text section that puts constants into memory
• Replicate the C stdlib functions in ASM
• Add a way to include another file to the project
• Implement stack system with returns
• Use WASM to make execution faster
• Add length calculation macro in TEXT
• Really put data byte by byte into memory

C Language improvements

• Handle any kind of C variables and C variable definition (e.g. char *test = "Hello World" abd char test[12] = "Hello World!" should do the same thing)
• Handle multi-arg functions call + returns
• Add for and while loops
• Add if else conditions
• Add ability to do chained conditions
• Do lexical analyser

Known Bugs

• Can't add labels with a comment on the same line
• Can't call a function with a quoted char as arg in C code
• Writing 'if (' or 'for' inside of the code editor is causing a crash fixed here
• Some C instructions are declared as errors/unrecognized. We need to fix C instruction types recognition
• When running C code, the line highlight isn't right
• for (int i = j; i < 5; i++) returns an error. Need to define i to 0 in TEXT section then define it before the for
• Cant stack 2 for. The compiler comments the second for
• for loops does not initialize var to the given value (only placed in TEXT)
• ; JMP operation is consierated as a number input instead of an instruction