add docs

README.md

@@ -1,10 +1,10 @@
-# UnnamedCPU
+# Dumb8-CPU
 
 Continuing my exploration of the lower-level world...
 
 This project is the implementation of a CPU in a high-level language, C. It aims to have a reduced (minimalist) instruction set and still be Turing complete.
 
-# How to test
+## How to test
 
 You can run a test program like that. I'll try making a developer's manual so one can make its own programs using the custom assembly here. 
 
@@ -13,8 +13,48 @@ make
 ./a.out program.asm
 ```
 
-# What I'd like to do
+## Technical specifications
 
-- Finish the instruction set implementation
-- Implement input/output devices (like a serial output that could be redirected to the host terminal)
-- Re-do the CPU in a Hardware Description Language, or even better: with transistors IRL! (i probably won't waste my life doing that tho)
+- 8-bit processing unit
+- RISC (reduced instruction set computer)
+- 4 general purpose registers (labeled R0 to R3)
+- 1 input port, 1 output port (via getchar and putchar)
+- Turing-completeness: bitwise and arithmetic operations
+
+## Instruction set reference (for programmers)
+
+```
+; Move register RY to register RX
+MOV RX, RY 
+
+; Arithmetic addition and substraction stored in RX
+ADD RX, RY
+SUB RX, RY
+
+; Bitwise operations stored in RX
+OR RX, RY
+AND RX, RY
+XOR RX, RY
+
+; Output RX to screen
+OUT RX
+
+; Input RX from keyboard
+IN RX
+
+; Jump to memory offset ADDR (decimal)
+JMP ADDR
+
+; Jump to memory offset ADDR (decimal) if equal flag is set by previous comparison
+JEQ ADDR
+
+; Compare RX and RY, sets equal flag if true
+CMP RX, RY
+
+; No operation; does nothing
+NOP
+
+; Halts the processing unit
+HLT
+
+```