What is Memory Mapped I/O? (16-Bit VM in JavaScript 005) @LowByteProductions

Uploaded December 2019 | Updated September 2026, 2 weeks ago

This this episode we implement memory mapped I/O, where the address space is utilised as common bus for components to communicate.

=[ ℹ About ℹ ]=

This series is all about building a powerful virtual machine in JavaScript with the following features:

- A flexible, extensible, register-based virtual machine
- Support for signed, unsigned and floating point operations
- A call stack
- Interrupt capabilities
- Ability to do memory mapping for IO
- An assembly language with macro and module support
- A higher level, C like language. We'll use and expand the library from the parser combinators from scratch series
- And finally, to be able to take the whole thing into the browser and exend it to create a sort of fantasy console - an emulator for a machine that never existed

=[ 🔗 Links 🔗 ]=

- ⭐️ Patreon: patreon.com/lowleveljavascript
- 💌 Updates to your inbox: tinyletter.com/lowleveljavascript

- Series Playlist: youtube.com/playlist?list=PLP29wDx6QmW5DdwpdwHCRJsEubS5NrQ9b&playnext=1&index=1

- Github Repo: github.com/LowLevelJavaScript/16-Bit-Virtual-Machine
- Memory Mapped IO: en.wikipedia.org/wiki/Memory-mapped_I/O
- Address Space: en.wikipedia.org/wiki/Address_space

What is Memory Mapped I/O? (16-Bit VM in JavaScript 005)

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$Fixed-point math is better than floating point (sometimes) In this video, were learning about fixed-point: A different method for doing non-integer arithmetic without floats! Floating point is a ubiquitous standard that works everywhere, but it needs specialised hardware to have any chance of running fast. This can make calculations on low-powered microcontrollers extremely expensive. Fixed-point solves, giving us a method for cheaply computing fractional results with flexible precision! 00:00:00 Intro 00:03:46 Floating point vs fixed point 00:10:07 Fixed point bit representation 00:17:10 Code: Fixed point defines 00:21:30 Getting to the integer and fractional parts 00:24:24 Sign function and representing ints in fixed point 00:32:14 Converting to and from floating point 00:36:23 Addition and subtraction 00:38:27 Multiplication 00:42:20 Division 00:48:52 Rounding operations 00:50:14 Absolute value 00:54:50 Floor 00:58:57 Getting the fractional part 01:02:38 Ceiling 01:05:37 Round 01:14:14 Motivating example: Analog to digital converter readings 01:30:10 Next time: Sines and cosines =[ 🔗 Links 🔗 ]= ⭐️ Become a patron and get bonus videos! https://www.patreon.com/lowleveljavascript 🗣 Discord: https://discord.gg/FPWaVgk 💻 Github Repo: https://github.com/lowbyteproductions/fixed-point-math$

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