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Post by buckoa51 on Jun 28, 2014 12:37:58 GMT
No reason why you could not that I'm aware of. The Action Replay combines the extra RAM with other functions too for instance.
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mick_aka
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Post by mick_aka on Jun 28, 2014 12:57:21 GMT
I was under the impression that the VCD slot was always the preferred expansion route.
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antime
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Post by antime on Jun 28, 2014 15:30:31 GMT
There are still several things I'm not sure how they're handled, but bandwidth and CD audio are not issues. The cartridge port sits on the same bus as the CD block, so data transfer speeds to the main memory should be identical. There is a pin on the cartridge port that selects if the SCSP's external audio input is taken from the CD block or the cartridge port.
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ray
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Post by ray on Jun 28, 2014 17:25:15 GMT
No reason why you could not that I'm aware of. The Action Replay combines the extra RAM with other functions too for instance. Using the save to memory cart feature in many Saturn games doesn't work with the Action Replay since the system apparently is unable to recognize a cartridge as multiple things. Transferring saves from the "Sarooo" to/from the Saturn in a boot menu obviously won't be a problem, but if the cartridge is already being used to load CD image data, is it possible to also have it function as a RAM cartridge or memory cartridge during gameplay? The AR's region unlocking and cheat codes aren't the same thing, as those functions aren't(as far as I know) being run continuously as the RAM expansion is.
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Post by buckoa51 on Jun 28, 2014 17:28:47 GMT
The AR cartridge has both expansion RAM and save game facilities, but you have to manually copy your save data from the Saturn to the cartridge when you are done playing.
As for if it is possible in this instance that entirely depends on how it is all implemented.
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Post by zyrobs on Jun 28, 2014 18:08:44 GMT
There are still several things I'm not sure how they're handled, but bandwidth and CD audio are not issues. The cartridge port sits on the same bus as the CD block, so data transfer speeds to the main memory should be identical. There is a pin on the cartridge port that selects if the SCSP's external audio input is taken from the CD block or the cartridge port. Ah, I see what caused me to think otherwise. I was looking at the wrong connector on the schematics (VA0 has two more connectors...). On VA0 you have a ribbon pin going into the OCU as cd audio, and a MPEG cart pin as mpeg audio. Then the OCU has a digital output pin that goes into a 74157, and so does the digital audio input on the cart port, and then the output from the muxer goes into the SCSP. On later models the ribbon cd audio pin goes through a VHC08 and I thought that was doing the muxing, but it seems to be something else. Other than that the setup is the same. On even later models the 74157 is omitted and instead IC6 is used to do the same thing with the digital audio. Also the cart port has both audio input and output, wtf. Which pin is the one you mention by the way? I see no option to select input, both (CD Block input) and (cart port input) goes into a 74157 multiplexer, and the output of that goes directly into the SCSP AUX pins.
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antime
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Post by antime on Jun 28, 2014 18:13:52 GMT
Transferring saves from the "Sarooo" to/from the Saturn in a boot menu obviously won't be a problem, but if the cartridge is already being used to load CD image data, is it possible to also have it function as a RAM cartridge or memory cartridge during gameplay? Yes. A cartridge can't function as eg. a RAM cart and save cart at the same time, because every cartridge type has an ID, and as far as is known, Sega didn't design a combined RAM+save cartridge so there is no type ID for having both functions simultaneously that games would recognize. Action Replay-type boot menus don't need a type ID and neither would this CD emulator.
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antime
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Post by antime on Jun 28, 2014 18:24:42 GMT
Which pin is the one you mention by the way? I see no option to select input, both (CD Block input) and (cart port input) goes into a 74157 multiplexer, and the output of that goes directly into the SCSP AUX pins. The SSEL pin (B3) is connected to the multiplexer's SEL input.
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Post by zyrobs on Jun 28, 2014 21:32:41 GMT
doh, right. I'm blind.
I really wonder how he is redirecting the cd calls to the cart. Can the CD Block access the cart on its own (as in, without the SH2s)?
I thought using the MPEG cart would be more optimal since you are communicating to the CD Block directly that way. Just patch it to redirect all the sector read commands to take data from there.
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antime
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Post by antime on Jun 29, 2014 9:59:17 GMT
My guess is that they're emulating the CD block, and that it's done by using the SMPC to issue a CDOFF command to keep the CD block in reset state, and then decoding and handling the accesses themselves. The /CS2 pin is brought out to the cartridge port, and the photos of the prototype show there's some kind of RAM on board (though it could of course just be used for buffering).
Any game that issued the SMPC CDON command would break this scheme, but I'm guessing they number somewhere between few and none.
If you wanted to use the MPEG port you'd have to backdoor the SH1 somehow, as no code from the cards should be executed normally (at least as far as I know).
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Post by zyrobs on Jun 29, 2014 14:58:01 GMT
If you wanted to use the MPEG port you'd have to backdoor the SH1 somehow, as no code from the cards should be executed normally (at least as far as I know). You can load encrypted sh1 code directly to the cd block, all mpeg carts work that way. The cd block does not have any mpeg functions, the cards upload them on boot. So you can also upload code to do something else.
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antime
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Post by antime on Jun 29, 2014 17:18:11 GMT
I was under the impression that any code present on the MPEG card was to be transferred to main memory and run from there, but I suppose they could have designed some kind of HAL system for different hardware. It is also kind of a gaping security hole.
Regardless, you'd still have to solve the bootstrap problem.
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Post by zyrobs on Jun 29, 2014 18:41:58 GMT
The MPEG card rom contains code before the typical Saturn rom. I was told that this is encrypted SH1 code that expands the SH1 "function set" and provides all the actual MPEG functions.
If you dump the mpeg rom from the Saturn side (with Cyberwarriors code for example), you'll have an offset shift that puts the typical Saturn header at the start, and this code at the back. The actual rom however has that code at the start.
There are of course some pitfalls (some possibly security related), once the good professor releases his docs we'll know more.
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antime
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Post by antime on Jun 30, 2014 4:26:29 GMT
If the code is only ever executed directly from the MPEG card ROM, it is accessed via the CD block LSI, which can decrypt it on the fly. On the other hand, if it's executed from the buffer RAM it has to be stored in clear text, which provides a pretty clear attack route.
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chk991
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Post by chk991 on Jul 8, 2014 4:11:28 GMT
I'll rather wait. Apparently the team behind PSIO are planning to work on a Saturn and a Dreamcast version. It'll probably be a little expensive but it's a lot less shady.
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