The IGS027A chips are meant to be scary boxes of hell, and in most cases they are.
** If used correctly **
I was looking at Demon Front and noticed something odd. Unlike ‘The Gladiator’ and most of the other later type games the code in the external ARM rom makes no reference to the internal ROM space. There are no obvious jumps back to the internal code area anywhere.
So I did a quick mod, wrote some fake ARM code to set up the stack pointer and then jump straight to the external area, and this happened.
Now while I can’t guarantee this is perfectly emulated because it’s possible the internal ARM code should be setting up some more things before jumping to the external code it’s still a huge surprise, and looks like a massive oversight when the game was developed. I guess the biggest surprise is that it’s taken until now to notice, it’s literally an 8-word patch.
My only theory is that maybe if this is the first game with an ‘Execute Only’ area IGS wanted to contain all the internal code in that area to make it more secure, but it has the opposite effect. I guess I should probe it a bit to see if there is anything interesting there at all.