32-Bit CPU

This project will simulate a running cpu with RISC-V architecture. It will also contain a custom assembly language and probably a compiler for C language.

General

This cpu has a 32Bit architecture. For this reason all instructions will be seperated into.
Instruction(8Bit) + Return-Register(8Bit) + Atribute 1(8Bit) + Atribute 2(8Bit)

Setup

Dependencies

• Logisim version 2.16.1.4
• CMake 3.0
• JDK >= 1.8

Instruction Set

A short description of whats the binary/hex equivalent to a given assembly instruction.
ALU/arithmetic instructions have code between 000 0001 and 0000 1111.

OP-Code(BIN/Hex)|    Assembly-Code      |       Atributes       |       Description
---------------------------------------------------------------------------------------------------------
0000 0000 (00)  |       NOP             | <No attributes>       | Execute no operation
0000 0001 (01)  |       ADD             | <Ret-Reg><Reg1><Reg2> | Add two values of given register
0000 0010 (02)  |       ADDI            | <Ret-Reg><Reg1><VALUE>| Add imidiate values onto register
0000 0011 (03)  |       SUB             | <Ret-Reg><Reg1><Reg2> | Subtract two register
0000 0100 (04)  |       SUBI            | <Ret-Reg><Reg1><VALUE>| Subtract a value from a register
0000 0101 (05)  |		MULT			| <Ret-Reg><Reg1><Reg2>	| Multiply two register
0000 0110 (06)  |		MULTI			| <Ret-Reg><Reg1><VALUE>| Multiply a register onto a value
0000 0111 (07)  |		DIV				| <Ret-Reg><Reg1><Reg2> |
0000 1000 (08)  |		DIVI			| <Ret-Reg><Reg1><VALUE>|
0000 1001 (09)	|			-			|						|
0000 1010 (0A)	|			-			|						|
0000 1011 (0B)	|			-			|						|
0000 1100 (0C)	|			-			|						|
0000 1101 (0D)	|			-			|						|
0000 1110 (0E)	|			-			|						|
0000 1111 (0F)	|			-			|						|
0001 0000 (10)	|		JMP				| <Pos-Arg1><Pos-Arg2>	| jump to an address with 16Bit!
0001 0001 (11)	|		BEQ*			| <Reg-Arg1><Reg-Arg2>	| Check if two register are equals
0001 0010 (12)	|		BNEQ			| <Reg-Arg1><Reg-Arg2>	| Check if two register aren't equals
0001 0011 (13)	|		PRNT			| <Reg-Arg1>			| Print something on display
0001 0100 (14)  |	 	RST*			|		   --			| Reset display
0001 0101 (15)  | 		READ*			| <Reg-Arg1>			| Read key input into the given register

*This operation is not implemented on hardware yet.

Register Design

Register	|	Alias		|	Description
---------------------------------------------------------------------------------------------------------
	x0	|	zero		| Hard wired zero register
	x1	|	ra		| Return address
	x2	|	sp		| Stackpointer
	x3	|	gp		| global pointer
	x4	|	tp		| Thread pointer
	x5-7	|	t0-2		| Temporary register
	x8-9	|	s0-1		| Saved register
	x10-11	|	a0-1		| Function arguments
	x12-15	|	s0-2		| Saved register	

Stack Pointer

Using my CPU as template, the stack pointer will be pre set at #FFFFF, because of the size for my register we'll be able to modify

Pipeline

The given pipeline has a depth of 2.

Example Code

To run specific code you need to fill up the RAM with HEX values. One example to write 5 into register 1 would look like this.
Instruction = 02 (ADDI), Return-Register = 01 (REG), First-Argument = 00 (ZERO), Second-Argument = 05 (HEX-VALUE of 5)
The complete instruction will be:

02010005 00000000 ...

To run this in logisim you need to write HEX code like this into a file and load it up in logisim as RAM values.