#145 Question about the SuperCPU support in Denise

[Anonymous]

Hello. First of all - Denise is a superb emulator and I am particularly fascinated by the fact, that it can emulate both, the C64 and the Amiga, since those are the two systems, I grew up with.

I have a question regarding the SCPU support in Denise. I never actually owned one of these, as a piece of hardware, but I wanted to experiment with it a bit now, using emulation to do so. If I understood correctly, from what I read online about the SCPU, then this hardware is connected in the normal cartridge-port (expansion port) and it features a passthrough port, allowing the user, to plug standard modules (such as AR6, FC3, etc) directly into it (behind it, on the C64). Does this also work with game-cartridges, or will only utility cartridges work this way, on a real C64? And if games do run this way, how does that work within Denise, when I want to run a game-cartridge simultaneously with the SCPU?

The reason I am asking is, that in the status-bar of Denise, the SCPU is always displayed as a normal cartridge and the CRT-LED is always on, as long as this SCPU is running. When running a game-cartridge in Denise, this cartridge-LED typically only lights up, when data is being loaded from the cartridge and I asked myself now, how it is represented visually in the status-bar, when combining a SCPU and a game-cartridge, that is reloading some datas? Or is it not possible in Denise, to run a game from a cartridge, while a SCPU is active and it only works with tool-cartridges that are not reloading at all?

I wondered a bit, when trying around with this thing in Denise, that the SCPU does not have an own LED in the status-bar, but is displayed there as a normal cartridge, only with permanent active LED. Could you please briefly explain the background, why it was done this way? I am completely new to the SCPU and maybe I'm overlooking something here?

Cheers,
Matthew

[PiCiJi]

I don't know which cartridges are compatible with the SuperCPU. There are likely very few, or rather, most combinations probably won't offer any added value. I can say with certainty that the SuperCPU and REU work together. You should ask this question in a forum.
SuperCPU has an own LED.
The SuperCPU LED lights up when the CPU is in 20 MHz mode; otherwise, it is in 1 MHz mode.

[Anonymous]

Thanks for fast replying. Ah okay, then probably only a few cartridges will work, when connected on the SCPU's passthrough port. Good idea, to ask this somewhere on a retro forum, will do so. But if that's the case, that only a few will run, that would be a bit sad, because I had asked myself, what kind of games could be possible, when running from big cartridges (instead of a disk) together with making use of the 20MHz mode of the SCPU. But then, this maybe will not work as I thought, sadly.
Last question. When you wrote "the SCPU has an own LED", then you mean, that it uses the same LED that cartridges use, but with different behavior, regarding the LED's illumination, right?

[PiCiJi]

Denise has no support for Super CPU + another CRT (except REU). that would be a todo, if I knew for sure that the SuperCPU and EasyFlash work together.
Sure, EasyFlash could contain a game like Test Drive, which could be accelerated by the SuperCPU.

If a cartridge utilizes a LED, it is displayed. Denise does not dictate when the LED should light up; rather, this is determined by the cartridge's internal logic. EasyFlash uses the LED to indicate access to the flash memory, while the SuperCPU uses it to signal 20 MHz operation.

[Anonymous]

Okay, understood. Thanks for the info about the LED behaviour. I didn't knew, that the internal logic of any cartridge determines this. Good to know.

Regarding the point about running cartridges with the SCPU. Since I read online, that the SCPU features a passthrough port, I concluded that, in principle, it should be possible, to use other cartridges together with the SCPU, at least as long as they do not occupy a memory range that the SCPU itself utilizes. I will try, to ask a person in a forum, that has a real SCPU, what experiences they have had, with cartridges connected behind the SCPU on the passthrough port.

[Anonymous]

In the meantime, I reached out to a few people in some retro-forums, who own a real SCPU hardware and the response I received was, that, while you can technically plug any cartridge into the SCPU's passthrough port, many of them (especially more complex utility cartridges) will not work perfectly. This is because they cannot cope with the altered timing, which is no longer precise, when the C64 is overclocked to 20MHZ. There does, however, seems to be a specific version of the Retro Replay cartridge, that could run with that, I was told, but with most other utility carts, there are problems. Also turning off the SCPU can not solve all the problems here, because there can be also problems with memory collisions.

Older Atari or C64 game cartridges, on the other hand, should generally work without issues. Things look less promising for newer EasyFlash cartridges, that rely on more complex bank-switching mechanisms, because here, conflicts with the SCPU's memory management system can appear. So, all in all, the outlook doesn't seem particularly good. It appears, that the pass-through port is primarily intended for specific applications, such as adding more RAM (via a RAM-disc e.g.) or connecting other proprietary expansions developed, by the SCPU manufacturer. That is the information I was given. Just wanted to pass it along here.

Cheers,
Matthew

[PiCiJi]

If a meaningful combination is known, one can pull up the ticket again.