Elements of Computing Systems

Introduction

I got started with this project after watching a couple videos that described the course. You can find them linked from the courses main webpage here. You can also find a study plan that describes all of the projects here.

Interesting Technical Information

Hardware

The hardware design is very simple/elegant (in my opinion). The processor has only two instructions. The first instruction is used to load an immediate value into the chips address register. The second instruction is sort of an "uber" instruction that does everything else. The instruction has optional destination registers for the result, various source registers, a calculation of some kind, and optional branch flags depending on the result of the calculation.

The calculations supported by the processor are very basic. You can do very simple math (add/subtract) and some bitwise operations (AND, OR, NOT). In fact all these math operations are implemented by setting "flags" on the ALU based directly on the instructions encoding. There is no need to do any sort of instruction decoding.

With just these two instructions it is possible to implement a complete computer system. More advanced operations (like multiplication) are implemented in software instead of in hardware like any modern processor.

Software

The course itself is often called Nand-to-Tetris because many people choose to implement Tetris to run on their "Hack" computer system. I chose to implement "Hacman" instead.

I actually had to write a somewhat optimized sprite routine just to draw Hacman and the 4 ghosts on the screen. To draw each frame I erase the sprites and redraw them in their new locations. Even with such simple rendering the framerate on the simulator is quite slow.

I am considering writing an efficient emulator of the Hack instruction set to see how fast I can emulate the chip.