Path: chuka.playstation.co.uk!news
From: "CRAIG GRAHAM" <c_graham@intelligent-group.com>
Newsgroups: scee.yaroze.programming.3d_graphics
Subject: Re: Move error (with source code)
Date: 8 Dec 1997 14:45:01 GMT
Organization: Intelligent Research Ltd
Lines: 85
Message-ID: <01bd03e8$d9ce16a0$6c0b0a0a@newcastle.twowaytv.co.uk>
References: <66gfjf$cel4@chuka.playstation.co.uk>
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Provenzano Stefano <dragon@azzurra.it> wrote in article
<66gfjf$cel4@chuka.playstation.co.uk>...
> Hi all,
> Very big problem:
> I have a program that move a 3D model around the world; using the arrows
I
> can rotate the model and than move it in that direction. Sometime occour
an
> error that stop the running and crash the psx, the error is:
> "ThePlayStation has generate an Illegal Instruction exception at
instruction
> address 0x8002861c".
> I have not any idea about this error, what instruction cause it and why.
> Can anyone read my souce code and then give me some hints??
> 
> Thanks in advance.
> 
>     Dragon
> 

Here's a sample of Dragon's code, the //++cg: bit's are my comments:

====INCLUDED CODE======
void ruota2 (GsCOORDINATE2 *coord_ogg, SVECTOR *vet_rot , int rx, int ry,
int rz )
{
	MATRIX *matTmp; //++cg: Here we have a pointer to a MATRIX, but it's
                                       //++cg: not been initialised to
actually point anywhere valid
 	
	ResetMatrix(coord_ogg->coord.m );
	
	vet_rot->vx = (vet_rot->vx+rx)%ONE;
	vet_rot->vy = (vet_rot->vy+ry)%ONE;
	vet_rot->vz = (vet_rot->vz+rz)%ONE;
	
	RotMatrix(vet_rot, matTmp); //++cg: Dragon now uses the invalid pointer...
	
	MulMatrix0(&coord_ogg->coord, matTmp, &coord_ogg->coord);
	
	coord_ogg->flg = 0;
}
==========================

Spot the problem? The variable matTmp is a pointer to a MATRIX, but it's
not actually pointing
at a MATRIX, it's pointing at a random place in memory - this is causing
corruption of the code,
hence the 

> "ThePlayStation has generate an Illegal Instruction exception at
instruction
> address 0x8002861c".

message Dragon is getting.....

Here's the fixed version (only for the one function, his code does this all
over the place so it need's
a fair bit of fixing):

void ruota2 (GsCOORDINATE2 *coord_ogg, SVECTOR *vet_rot , int rx, int ry,
int rz )
{
	MATRIX matTmp;  //++cg: This is now a real MATRIX, NOT a pointer
 	
	ResetMatrix(coord_ogg->coord.m );
	
	vet_rot->vx = (vet_rot->vx+rx)%ONE;
	vet_rot->vy = (vet_rot->vy+ry)%ONE;
	vet_rot->vz = (vet_rot->vz+rz)%ONE;
	
	RotMatrix(vet_rot, &matTmp); //++cg: Initialise the rotation matrix by
getting a pointer to matTMP
	
	MulMatrix0(&coord_ogg->coord, &matTmp, &coord_ogg->coord); //++cg: again,
get a pointer to matTMP
	
	coord_ogg->flg = 0;
}

Laters,
Craig.