Load block from CDROM (PCE/TG16)

I love the PCE and figured I’d share some of the things I’ve been learning about it. So my next couple of posts will be about different things I’ve learned. For any PCE hacking I wholeheartedly recommend Mednafen. One thing I noticed that is not documented though is that if you hit L on the debug screen (hit ALT + D, ALT + 1) it’ll bring up a window where you can type in the file name you want to trace out to. Very useful feature as I find it easier to look at a trace then at a debug screen when first analyzing something. Anyways, on to the whole point of the post…

For our example, were looking at Tengai Makyou Ziria. For TMZ, it’ll load into one of the MPRs the bank location in RAM it wants to write to (in my case it was MPR5, I’m not sure if it matters, although it did load MPR6 with the next bank). You then call the subroutine at 0xE009. In your trace you can then look for reads from location 0x1808 or just search for the location in the MPR it’s writing too (in my case I looked for 0xA000).

One thing I’ll check into and look for is if you can specify how many blocks to load as it loads in 0x800 (2048) blocks. I’ll update this later when I find out…

Finding the text…

Alrighty, let’s get started.

I do want to warn though, for finding stuff like this, it requires a lot of patience and a lot of guess work (as you’ll see below). By no means will this work for every game but I hope this will help somehow.

For this I recommend you read the document located here : DMA Transfers, Compression, and You

This document describes how were going to find the font but using a different game called Filerna. I’ll of course explain here how I’m going about finding the font as well.

For our utilitie I recommend Geiger’s Snes9x Debugger located here : Romhacking.net, click on Utilities, from the category dropdown select Special Emulators/Debuggers, for Platform dropdown, select Super Nintendo and click ok.

And also ZSNES (it’s easier to dump the VRAM with this). ZSNES

For our tile editor, I recommend YY-CHR located at Romhacking.net, search for YY-CHR.

Introduction

Welcome one and all!

Looking around I noticed there really aren’t too many tutorials/howto that go into the assembly side of hacking games.  I’m hoping with this blog that I can go into some of how this is done.  I’m only talking about how to figure out compression/encryption schemes for graphics and text though.  I’m in no way talking about cracking a game to get around copyright protection so if you’re looking for that or asking how to go about doing it, you might as well leave as I can’t help you there.

For the best place to find documents relating to assembly hacking (and rom hacking in general), check out Romhacking.net. I’ll be referencing some of the docs here pointing out the techniques I learned from them that we’ll apply.

For the first game we’ll be looking at the font and text in Shin Megami Tensei If… for the SNES by Atlus.

I recommend checking out Romhacking.net and looking at the docs there on the SNES. Also, I’m not teaching how to romhack here (although I may explain some things) so I definitely recommend looking at some of the newbie guides on there.