mirror of
https://github.com/hsoft/collapseos.git
synced 2024-11-01 23:10:55 +11:00
90 lines
3.1 KiB
Plaintext
90 lines
3.1 KiB
Plaintext
# Sega Master System
|
|
|
|
The Sega Master System was a popular gaming console running on
|
|
z80. It has a simple, solid design and, most interestingly of
|
|
all, its even more popular successor, the Megadrive (Genesis)
|
|
had a z80 system for compatibility!
|
|
|
|
This makes this platform *very* scavenge-friendly and worth
|
|
working on.
|
|
|
|
SMS Power[1] is an awesome technical resource to develop for
|
|
this platform and this is where most of my information comes
|
|
from.
|
|
|
|
This platform is tight on RAM. It has 8k of it. However, if you
|
|
have extra RAM, you can put it on your cartridge.
|
|
|
|
# Gathering parts
|
|
|
|
* A Sega Master System or a MegaDrive (Genesis).
|
|
* A Megadrive D-pad controller.
|
|
* A way to get an arbitrary ROM to run on the SMS. Either
|
|
through a writable ROM cartridge or an Everdrive[2].
|
|
|
|
# Hacking up a ROM cart
|
|
|
|
SMS Power has instructions to transform a ROM cartrige into a
|
|
battery-backed SRAM one, which allows you to write to it through
|
|
another device you'll have to build. This is all well and good,
|
|
but if you happen to have an AT28 EEPROM, things are much
|
|
simpler!
|
|
|
|
Because AT28 EEPROM are SRAM compatible, they are an
|
|
almost-drop-in replacement to the ROM you'll pop off your
|
|
cartridge. AT28 are a bit expensive, but they're so handy! For
|
|
SMS-related stuff, I recommend the 32K version instead of the 8K
|
|
one because fitting Collapse OS with fonts in 8K is really
|
|
tight.
|
|
|
|
The ROM cartridge follow regular ROM pinout, which means that
|
|
A14 are just under VCC, where WE is on the AT28. We need WE to
|
|
be perma-disabled and A14 to be properly connected.
|
|
|
|
1. De-solder the ROM
|
|
2. Take a 28 pins IC socket
|
|
3. Cut off its WE pin (the one just under VCC), leaving a tiny
|
|
bit of metal.
|
|
4. Hard-wire it to VCC so that WE is never enabled.
|
|
5. Solder your socket where the ROM was.
|
|
6. With a cutter, cut the trace leading to A14.
|
|
7. Wire A14 to the trace just under WE (which doesn't actually
|
|
touch WE because we've cut the IC socket's pin).
|
|
8. Insert Collapse OS-filled EEPROM in socket.
|
|
|
|
As simple as this! (Note that this has only been tested on a SMS
|
|
so far. I haven't explored whether this can run on a megadrive).
|
|
|
|
# Build the ROM
|
|
|
|
Running "make" in /arch/z80/sms will produce a "os.sms"
|
|
ROM that can be put as is on a SD card to the everdrive or
|
|
flashed as is on a writable ROM cart. Then, just run the thing!
|
|
|
|
To run Collapse OS in a SMS emulator, run "make emul".
|
|
|
|
# Usage
|
|
|
|
Our input is a D-Pad and our output is a TV. The screen is 32x28
|
|
characters. A bit tight, but usable.
|
|
|
|
D-Pad is used as follow:
|
|
|
|
* There's always an active cursor. On boot, it shows "a".
|
|
* Up/Down increase/decrease the value of the cursor.
|
|
* Left/Right does the same, by increments of 5.
|
|
* A button is backspace.
|
|
* B button skips cursor to next "class" (number, lowcase,
|
|
upcase, symbols).
|
|
* C button "enters" cursor character and advance the cursor by
|
|
one.
|
|
* Start button is like pressing Return.
|
|
|
|
Of course, that's not a fun way to enter text, but using the
|
|
D-Pad is the easiest way to get started which doesn't require
|
|
soldering. Your next step after that would be to build a PS/2
|
|
keyboard adapter! See smsps2.txt
|
|
|
|
[1]: http://www.smspower.org
|
|
[2]: https://krikzz.com
|