Comp

Simple 4-bit/1 Hz virtual computer for learning purposes

Memory

instructions - 4 bits
  |  +-- addresses - 4 bits
  v  v
----***-  <- 0  ----
--*-**-*  <- 1  ---*
---***--  <- 2  --*-
---*****  <- 3  --**
----***-  <- 4  -*--
---***-*  <- 5  -*-*
----**--  <- 6  -**-
---****-  <- 7  -***
-***---*  <- 8  *---
-*--****  <- 9  *--*
--------  <- 10 *-*-
--------  <- 11 *-**
--------  <- 12 **--
-------*  <- 13 **-*
-------*  <- 14 ***-
<OUTPUT>  <- 15 ****

Execution starts at the first address (0).
Execution stops when program reaches last address (15).
Whatever gets written to the last address is sent to the printer.
Computer has one 8 bit register.
When reading from the last address (15), we get a random byte value.

Instruction set

READ ---- - Copies the value at the specified address into register.
WRITE ---* - Copies value of the register to the specified address.
ADD --*- - Adds value at the specified address to the value of the register, and writes result to the register. If the result is bigger than the maximum possible value (255 = ********) then 255 gets written.
SUBTRACT --** - Subtracts value at the speicfied address from the value of the register, and writes result to the register. If the result is smaller than 0 then 0 gets written.
JUMP -*-- - Changes the value of the program counter to the specified address, meaning that in the next cycle execution will continue at that address.
IF MAX -*-* - Jumps to the specified address if register has value 255 = ********.
IF MIN -**- - Jumps to the specified address if register has value 0 = --------.
SHIFT R -*** - Moves every bit of the register one spot to the right. This way rightmost bit gets lost, and a leftmost becomes '-'. This is the only instruction that doesn't use the address part, making the last four bits irrelevant.
Any instruction that is not defined above gets interpreted as READ ---- instruction.

How to run on…

Windows

Download and install wget
Open Command Prompt
Go to the directory where you want Cygwin installed
Install and start Cygwin:

setx PATH "%PATH%;C:\Program Files (x86)\GnuWin32\bin" wget --no-check-certificate https://cygwin.com/setup-x86_64.exe mkdir cygwin setup-x86_64.exe --quiet-mode --no-shortcuts --site http://cygwin.mirror.constant.com --root %cd%\cygwin -P git -P gcc-g++ -P ncurses -P vim-common -P libgcc1 -P libclang-devel -P make -B cygwin\Cygwin.bat


* Run the *UNIX* commands  

### UNIX
```bash
git clone https://github.com/gto76/comp-cpp.git
cd comp-cpp
bash run

Example programs