RPCEmu bank switching crashes and/or hangs RISCOS

I’m trying to get bank switching up and running, and for some reason one of the following always happens :

A) RPCEmu crashes (typically with a Bad Read CP15 error or Bad Op Code)
B) RiscOS crashes (abort on data fetch)
C) GCC crashes and will no longer compile (SWI missing or some other “error”)

Is this a problem with RPCEmu or a problem with RiscOS 5 ?

It’s difficult to judge unless you give us the code you’re using. Speaking from experience with such queries, it’s entirely possible you’re doing it wrong.

Yes, its possible. However, I dont know why its wrong

The code is thus :

		inreg.r[0]=114;
		inreg.r[1]=0;
		_kernel_swi(OS_Byte,&inreg,&outreg);

		if (sH<0)
		{
			// Old mode system
			inreg.r[0]=0;
			inreg.r[1]=sW;
			_kernel_swi(OS_ScreenMode,&inreg,&outreg);

			// Get the screen resolution
			inreg.r[0]=-1;
			inreg.r[1]=11;
			_kernel_swi(OS_ReadModeVariable,&inreg,&outreg);
			sW=outreg.r[2]+1;

			inreg.r[0]=-1;
			inreg.r[1]=12;
			_kernel_swi(OS_ReadModeVariable,&inreg,&outreg);
			sH=outreg.r[2]+1;
		}
		else
		{
		int modeSelectBlock[7];

			// New mode system
			modeSelectBlock[0]=1;
			modeSelectBlock[1]=sW;
			modeSelectBlock[2]=sH;
			modeSelectBlock[3]=3;
			modeSelectBlock[4]=-1;
			modeSelectBlock[6]=-1;

			inreg.r[0]=0;
			inreg.r[1]=(int) &modeSelectBlock;
			_kernel_swi(OS_ScreenMode,&inreg,&outreg);
		}

			// Readjust screen area for bank switching
			// Get screen size
			inreg.r[0]=-1;
			inreg.r[1]=7;
			_kernel_swi(OS_ReadModeVariable,&inreg,&outreg);
			requiredSize=outreg.r[2]<<1;

			// Get current screen area size
			inreg.r[0]=2;
			_kernel_swi(OS_ChangeDynamicArea,&inreg,&outreg);

			sizeIncrease=requiredSize-inreg.r[1];
			if (sizeIncrease>0)
			{
				inreg.r[0]=2;
				inreg.r[1]=sizeIncrease;
				_kernel_swi(OS_ChangeDynamicArea,&inreg,&outreg);
			}

void TSetup_Base::Flip(void)
{
	inreg.r[0]=112;
	inreg.r[1]=bank;
	_kernel_swi(OS_Byte,&inreg,&outreg);

	bank=(bank==1 ? 2 : 1);  // Need to check the maximum number of screens available...

	inreg.r[0]=113;
	inreg.r[1]=bank;
	_kernel_swi(OS_Byte,&inreg,&outreg);

	// Clear screen
	inreg.r[0]=0x10C;
	_kernel_swi(OS_Byte,&inreg,&outreg);

	// Do VSYNC
	inreg.r[0]=19;
	_kernel_swi(OS_Byte,&inreg,&outreg);

	inreg.r[0]=250;
	inreg.r[1]=0;
	inreg.r[2]=255;
	_kernel_swi(OS_Byte,&inreg,&outreg);

	printf("Here\n"); getchar();
}

Still trying to work out why it crashes (and the second bank is basically corrupt)…

According to OS_Byte 250, the banks are switching correctly between 1 & 2

The only thing I was wondering about is whether OS_Byte 114 should be called before or after a screen resolution change.

It does look as I’ve solved it. It appears that the cause was activating 2Mb of VRAM in the emulator – switch that off and all is okay. Unfortunately I’m now limited to a 640 × 480 display, but it will have to do…