Calcu-16

Calcu-16 is a processor I made to help me learn verilog.

At first the plan was to make a module for each part of the processor and attach them together in a core module but I couldn't get it to work. The problem was that if I attach the output of the register module to input a of the alu module the output of the alu becomes x. This only happened when one output of the register module was 0. You can see my first attempt in the old_attempt folder.

Registers

Calcu-16 has eight general purpose registers named r0-r7. Each register is 16-bits wide. There are two other registers, the IR (Instruction Register 26-bit) and the PC (Program Counter 16-bit).

Instruction formats

Register Format

 0:3     4:6 7:9 10:12
 op-code registers       unused
  │           │              │
 ┌┴─┐ ┌───────┴─┐ ┌──────────┴┐
 0000 000 000 000 0000000000000
      └┬┘ └┬┘ └┬┘
      r1  r2  r3

Immediate/Memory Format

 0:3     4:6   7:9 10:25
 op-code registers immediate/addr
  │        │        │
 ┌┴─┐ ┌────┴┐ ┌─────┴────────┐
 0000 000 000 0000000000000000
      └┬┘ └┬┘
      r1  r2

Instructions

Instruction	Op-Code	Format	Description
nop	0000	N/A	Does nothing.
add reg1, reg2, reg3	0001	Register	Adds reg2 to reg3. Stores the result in reg1.
addi reg1, reg2, Imm	0010	Immediate	Adds reg2 to Imm. Stores the result in reg1.
jmp addr	0011	Memory	Sets the PC to the value of addr.
jeq reg1, reg2, addr	0100	Memory	If reg1 = reg2 then jump to addr.
store reg1, reg2, addr	0101	Memory	Store reg1 at addr + reg2.
load reg1, reg2, addr	0110	Memory	Load reg1 with the value stored at addr + reg2.
xor reg1, reg2, reg3	0111	Register	XOR reg2 and reg3 put the result in reg2.
and reg1, reg2, reg3	1000	Register	AND reg2 and reg3 put the result in reg2.

Building

To build Calcu-16 from source you must run build.sh.

Programming

To run a program open bin/program.bin and uncomment the program you want to run. Then open a terminal and type:

cd bin
./calcu16

If you want to write your own program just add it to the end of bin/program.bin. To make writing the program easier you could use my assembler although I don't recomend it. Also, feel free to contribute any programs you make to the programs.bin file.

If you want to create a .vcd wave file then open src/calcu-16.v and src/calcu-16_tb.v. Find the part in each file where it says "Uncomment for debugging" and uncomment the following lines.

Using The Assembler

To use the assembler open the assembler folder. To assemble the example counter program use the folowing command:

python assembler.py counter.asm counter.bin

This will create a file called counter.bin which you can then copy the contents of into the bin/program.bin file.

You can write your own assembly programs and assemble them with the folowing format:

python assembler.py [your program.asm] [name of the output file.bin]