VMU (Visual Memory Unit)
The Sega Dreamcast had a peripheral called the VMU (Visual Memory Unit). The VMU is a memory card, but it also has a small (48x32) monochrome display, 4 buttons, and a direction pad.
It's possible to load one game at a time onto a VMU from the Dreamcast, and then take the VMU with you as a handheld gaming device.
waterbear
I've written an open source assembler/disassembler for the VMU called waterbear (download the latest release from here). You can read the documentation here.
VMU Development Resources
The Dreamcast Wiki has a lot of resources for VMU development: https://dreamcast.wiki/VMU_development.
Posts
The Genesis of waterbear
2023-01-14
How
waterbear got its start.
Release 0.18.0 of waterbear: .include icon and more
2020-12-10
This release adds features to simplify creating VMS headers.
Release 0.2.0 of waterbear: disassemble
2018-11-03
Release 0.2.0 of
waterbear, which adds the disassemble command
First release of waterbear!
2018-09-01
The first release of
waterbear, an assembler for the Dreamcast VMU