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  • Joined: 24 Jun 1999
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  • Location: Paris, France
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Interrupt Generated by Hardware
Post Posted: Fri Jul 23, 1999 11:58 pm
Me and James McKay are studying a CodeMasters game in order to dump and emulate it.
Of course CodeMasters doesn't do things like others, so they use different place to map the cartridge area to the main memory space and use an expanded video mode that no other games uses and no emulators supports (yet).
So far James went to a point were the code got stuck in a loop waiting for an interrupt. But interrupts were disabled, judging by the VPD registers values. So the question is:
"it is possible that a cartridge could generate an interrupt ?" (does it have access to the IRQ or NMI line)
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Eric
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Post Posted: Sat Jul 24, 1999 3:49 am
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> Me and James McKay are studying a CodeMasters game in order to dump and emulate it.
> Of course CodeMasters doesn't do things like others, so they use different place to map the cartridge area to the main memory space and use an expanded video mode that no other games uses and no emulators supports (yet).
> So far James went to a point were the code got stuck in a loop waiting for an interrupt. But interrupts were disabled, judging by the VPD registers values. So the question is:
> "it is possible that a cartridge could generate an interrupt ?" (does it have access to the IRQ or NMI line)

According to the pin-out information I have, virtually the entire system bus is routed to the cartridge port.

Pin 50 is labeled NMI. Pin 38 is labeled I/OReq. It seems very likely (almost certain in the case of NMI) that these
two pins are connected to the Z80's NMI and INTR pins, respectively. Consequently, it is likely that a cartridge
could generate an interrupt request. However, this would only make sense if the cartridge had some
sort of timer on it.

I will try to confirm how this bus lines connect to the Z80.

Eric
 
Eric
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Post Posted: Sat Jul 24, 1999 4:53 am

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> Pin 50 is labeled NMI. Pin 38 is labeled I/OReq. It seems very likely (almost certain in the case of NMI) that these
> two pins are connected to the Z80's NMI and INTR pins, respectively. Consequently, it is likely that a cartridge
> could generate an interrupt request. However, this would only make sense if the cartridge had some
> sort of timer on it.

> I will try to confirm how this bus lines connect to the Z80.

I was unable to absolutely confirm that Pin 50 (NMI) is connected to the NMI pin on the Z80, though it certainly is possible.

Regarding the Z80 INT pin, it is most definitely connected to Pin 42 (INT) on the cartridge port (NOT pin 38, I/OReg is a different Z80 pin. I don't know what I was thinking before.) This means that a cartridge could easily generate it's own (maskable) interrupt request.

I suggest you try to determine if the Code Masters cartridge pin 42 is actually connected to something on the cartridge chips. If so, you may be right, the cartridge could be generating it's own interrupts.

Hope this helps.

Eric
 
  • Joined: 24 Jun 1999
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  • Location: Paris, France
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Post Posted: Sat Jul 24, 1999 10:50 am
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> I suggest you try to determine if the Code Masters cartridge pin 42 is actually connected to something on the cartridge chips. If so, you may be right, the cartridge could be generating it's own interrupts.

Problems is that cartridge are weird, rounded, and un-openable at my knowledge.
Opening it *could* broke it. I'll see what I can do.
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  • Joined: 12 Jul 1999
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Post Posted: Sun Jul 25, 1999 7:07 am
Codemaster catridges are held together by two weird-arsed scews under the label and two clips at the top of the cartridge.
You take the label off, find the appropriate screwdriver (a five-pointed star with a dent in the middle, if my memory serves me correctly), take the screws out and *gently* lift the face of the cartridge off from the bottom up. I think.
Hope this helps,
-unfnknblvbl
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  • Joined: 24 Jun 1999
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Post Posted: Sun Jul 25, 1999 10:45 am
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> Codemaster catridges are held together by two weird-arsed scews under the label and two clips at the top of the cartridge.
> You take the label off, find the appropriate screwdriver (a five-pointed star with a dent in the middle, if my memory serves me correctly), take the screws out and *gently* lift the face of the cartridge off from the bottom up. I think.

There are absolutly no screws on the cartridge.
Anyway, I found a way to open it. Needless to say, it was brand new before and now it is in very bad condition, but it is still working and that's all that matter :)
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Flavio
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My two cents
Post Posted: Wed Jul 28, 1999 5:13 am
[Disclaimer: My SMS pinout schematic doesn't display pin numbers, just their names]

The leftmost pin on the upper (component) side of an SMS connectors generates an NMI if grounded.
The fifth pin from the left, again on the component side, generates a regular interrupt when grounded.
Definitely, carts *can* interrupt the SMS.

Cheers,
Flavio.
 
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