peppergrayxyz / Potato-1

Brainfuck CPU for tinytapeout

Home Page:https://www.tinytapeout.com

Geek Repo:Geek Repo

Github PK Tool:Github PK Tool

Potato-1

Potato-1 is part of a Brainfuck CPU. It is only the control logic, i.e. you have to bring your own registers, memory controller and io logic. It is very simple, hence likely very slow: You could probably run your brainfuck code on a potato and it would be equally fast, hence the name. The project picture was generated using DALL·E. Potato-1 is a project submitted to TinyTapeout to be fabricate as an ASIC.

Potato-1 teaser picture

Overview

Potato-1 is a control unit, which processes 4bit instructions and controls CPU registers accordingly. It is designed in a very simple and minimalistic way, i.e. there is only the bare minimum to execute brainfuck code. Most commands are straight forward and can be passed through as they are, i.e. increment/decrement value and data pointer, put and get value.

Architecture

Loops requiere some logic is, but there is no stack, neither are there jumps or labels to jump to. Insteady the code is executed in reverse direction to execute loops. To find the matching '[' or ']' a 16bit counter is used. Each loop instruction will increment or decrement the counter accordingly. If we skip from start to end or end to start, the target value is stored in another register. If both values match, the execution continous. As there is no jump instruction, the programm is executed one instruction at a time, but if the CU 'jumps' intermediate instructions are ignored. If the 'jump' is from end to start, the execution direction is reversed, i.e. the program counter is decrement until the matching loop instruction is found.

Read an write instructions relay on some external IO logic, which puts the value to some kind of IO or gets a value from there. IO indicates that it is no yet done with the IO-Wait pin.

Input Signals:

Pin Signal Description
0 Clock
1 Reset_n active low
2 IO Wait wait till Put/Get from/to value is done
3 Zero Flag indicate that value is zero
4-7 Instruction 4bit instruction

Each rising edge the CU will read in the instruction, zero flag and IO Wait flag and process it. Each falling edge the output pins will be updated. The output pins indiciate which action to take, i.e. which registers to increment/decrement. If Put or Get pin is set, the CU will pause execution until IO Wait is unset. If IO Wait is already unset, the CU will immidiatly execute the next command without waiting.

Output Signals

Pin Signal Description
0 PC++ increment program counter
1 PC-- decrement program counter
2 X++ increment data pointer
3 X-- decrement data pointer
4 A++ increment value
5 A-- decrement value
6 Put write value
7 Get read value

Instructions

Additionaly to the 8 original brainfuck instructions there is a HALT instruction to stop execution and a NOP instructions to do nothing, also there are unused instruction (some of them may be used to extend the instruction set in a later itteration).

Commands:

Opcode Mnemonic Description
0000 > Increment the data pointer
0001 < Decrement data pointer
0010 + Increment value
0011 - Decrement value
0100 . Write value
0101 , Read value
0110 [ Start Loop (enter if value is non-zero, else jump to matchin ']')
0111 ] End Loop (leave if value is zero, , else jump to matchin '[')
1000 NOP No Operation
1111 HALT Halt Execution

Simulation

https://peppergrayxyz.github.io/Potato-1/simulator/

Circuit

Potato-1 circuit

Layout

3D Render

Potato-1 circuit

About Tiny Tapeout

TinyTapeout is an educational project that aims to make it easier and cheaper than ever to get your digital designs manufactured on a real chip!

About

Brainfuck CPU for tinytapeout

https://www.tinytapeout.com

License:Apache License 2.0


Languages

Language:Python 56.7%Language:Verilog 20.6%Language:JavaScript 9.8%Language:Tcl 6.5%Language:HTML 4.4%Language:Makefile 1.9%