Mysterious error message ?

ivanb303 · December 2016

Something just occurred to me, when I try to load certain JSW games which require 128k memory into my emulator in 48K mode I get this error message.

4 Requires 128k memory, 40:1

Doesn't that strike you as weird ? Is that error message in the original ROM from 1982 ?! How did they know they were gonna make a 128k Speccy! Isn't there anything Clive can't do ? He's a time traveller too :)

AndyC · December 2016

Do you have an example? The most likely cause is the game itself is detecting the issue and reporting the error (though why it would show up in that specific format seems odd, unless something is hooking the error handling code)

ivanb303 · December 2016

This is in Marvin on Android I've tried to load one of JSW128 games from 48k mode.

https://www.dropbox.com/s/a1ofznfus3t0tfa/Screenshot_20161208-004153.png

ivanb303 · December 2016

Can you see that ?

ivanb303 · December 2016

I just tried it on Speccy on Android same thing happens :)

ivanb303 · December 2016

Try loading JSW - Join the Jet Set on your emulator running in 48k mode

GReW · December 2016

The only version of "JSW - Join the Jet Set" I can find is from 1985 and works perfectly on the 48K Spectrum (which is hardly surprising).

Are you referring to a remake of the game for the 128k? In which case, the loader obviously checks that it's running on the correct machine and displays a custom error message. Whether it hijacks the ROM error routine or (more likely) just prints it to the lower screen, the message itself isn't in ROM.

ivanb303 · December 2016

Take a look at something like Jet Set Willy - Dragon64 :) Put your emulator in 48 mode and load it

AndyC · December 2016

It looks like something the JSWED engine does, you can see the message in RAM when it loads. I suspect it's hooking the error message response somehow, so that it doesn't immediately get overwritten by the 0 OK message.

John Elliott · December 2016

Generating a custom error message as JSW64 does here is quite fiddly, because you need separate versions depending whether you're running in 48BASIC, 128BASIC or +3BASIC. The VERS subroutine (which I haven't provided) looks at various locations in the ROM to detect 48k (H=0), 128k (H=1), +3 (H=2) or unknown (H=0FFh).

Enter with DE = address of custom error message, bit 7 set on last character.

ZXERR:	LD	(MSERR),DE	;Error string
	LD	IY,5C3AH	;Spectrum system veriables
	EI
	CALL	VERS		;This is done differently on 128s, 48s and +3s
	LD	A,H
	OR	A
	JR	Z,BERR48
	DEC	A
	JP	NZ,BERRP3
;
;Running on a 128.
;
	BIT	4,(IY+1)	;Running 128 BASIC?
	JR	Z,BERR48	;No; 48 mode is assumed.
	LD	HL,(5B8BH)	;Fake a 128 BASIC error.
	LD	(MSRET),HL
	LD	HL,0397H	;Jump in after the part which determines the
	LD	(MSMES+1),HL	;address of the message.
	LD	HL,ERRRT1
	LD	(5B8BH),HL
	JP	23325		;Page in ROM 1 etc.
;
ERRRT1:	LD	HL,(MSRET)
	LD	(5B8BH),HL	;Restore old SYNRET.
	LD	SP,(RAMTOP)	;Clear machine & GOSUB stacks.
	INC	SP
	LD	HL,5BFFH
	LD	(5B81H),HL	;OLDSP
	HALT
	RES	5,(IY+1)
	LD	HL,5B66H
	BIT	2,(HL)
	JP	Z,R034A	;$+14
	CALL	1F45H
	LD	IX,(5B83H)
	LD	BC,14H
	ADD	IX,BC
	CALL	1D56H
	CALL	1F20H
	JR	R034A
;
BERR48:	HALT
	RES 	5,(IY+01H)
	BIT 	1,(IY+30H)
	CALL	NZ,0ECDH
	LD  	HL,0
	LD  	(IY+37H),H
	LD  	(IY+26H),H
	LD  	(5C0BH),HL
	LD  	HL,1
	LD  	(5C16H),HL
	CALL	16B0H
	RES 	5,(IY+37H)
	CALL	0D6EH
	SET 	5,(IY+02H)
	LD	DE,(MSERR)
L0C22:	LD	A,(DE)
	AND	7FH
	CALL	0C3BH
	LD	A,(DE)
	INC	DE
	ADD	A,A
	JR	NC,L0C22
	JP	1349H
;
BERRP3:	BIT	4,(IY+1)	;Running +3BASIC?
	JR	Z,BERR48	;No; 48 mode is assumed.
	LD	HL,(SYNRET)	;Fake a +3BASIC error.
	LD	(MSRET),HL
	LD	DE,61H
	ADD	HL,DE		;Jump in after the part which determines the
	LD	(MSMES+1),HL	;address of the message.
	LD	HL,ERRRTN
	LD	(SYNRET),HL
	JP	ONERR		;Page in ROM 1 etc.
;
ERRRTN:	LD	HL,(MSRET)
	LD	(SYNRET),HL	;Restore old SYNRET.
	LD	SP,(RAMTOP)	;Clear machine & GOSUB stacks.
	INC	SP
	LD	HL,5BFFh
	LD	(OLDSP),HL
	HALT
	RES	5,(IY+1)
R034A:	LD	HL,0
	LD	(IY+55),H
	LD	(IY+38),H
	LD	(5C0BH),HL
	INC	HL
	LD	(5C16H),HL
	RST	28H
	DEFW	16B0H
	RES	5,(IY+55)
	RST	28H
	DEFW	0D6EH
	SET	5,(IY+2)
	LD	DE,(MSERR)	;Address of error message.
MSMES:	JP	0

MSRET:	DEFW	0
MSERR:	DEFW	0
;
not128:	defb	'4 Requires 128k memor'
	defb	0F9h			;'y'+128
;
	end

Mysterious error message ?

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