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recipes/sms: add cartridge hacking instructions

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Virgil Dupras 2020-10-12 21:39:53 -04:00
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recipes/sms/README.md
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@ -21,18 +21,41 @@ are other recipes related to the SMS:
## Gathering parts
* [zasm][zasm]
* A Sega Master System or a MegaDrive (Genesis). (I have only tested on a
MegaDrive so far)
* 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 card or an [Everdrive][everdrive].
ROM cartridge or an [Everdrive][everdrive].
## 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.
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. 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` 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!
Running `make os.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
@ -64,4 +87,3 @@ seconds. It's the emulator's fault. On real hardware, it's not as slow.
[smspower]: http://www.smspower.org
[everdrive]: https://krikzz.com
[zasm]: ../../tools/emul