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2nd prototype connectors

  • Hi there,

    in this blog post there is a picture of the 2nd prototype of the MEGA65:
    http://www.m-e-g-a.org/de/mega-65-second-prototype/

    The prototype looks absolutely fantastic - just like the original!

    But also the connectors on the backside look pretty much like the original (just click through the pics, it's more than just those 3 preview pics and on one of them you can clearly see the back with the connectors).

    I wonder if this is a bit "fake" (to get some nice pictures) or if they all are really working? And if so, how are they connected to the Nexys board, or does this prototype already contain a custom board?

  • Again: This prototype resembles the exact state where Commodore abandoned the C65. It was part of our plan to reach that state instead of doing changes to the machine before we reach that goal, so -in our world- we really enhance the C65 to become a MEGA65 and not just build a fantasy machine that abandons or ignores principles of the original computer.

    So, yes, this case is a 100% replica of the original case and from now on there will be tiny and careful modifications to it mostly regarding the ports. It has been remodelled from the original (which we also own) by MEGA. And no, we will not mass- produce this version of the case.

    Yes again, inside is a super exact replica of the original C65 board by Wayne of which we proudly own two (besides a fully polluted and working original C65 mainboard), of course missing some custom chips but other than that working perfectly.

    The keyboard in this prototype is an original keyboard from Mitsumi. We have now cracked the keyboards nut and our own keyboards will be very similar. The case obviously will be aswell :)

    Hope that clears it once and for all ;)

    cheers
    Deft

  • Okay thanks for clarification. So this is a different clone (Wayne's clone)? Who is Wayne and why have I never heard about his clone so far? :)

    Is it a unique piece by an enthusiast or was it made as part of the MEGA65 development?

  • Absolutely right. He built 10 boards in total but could only populate 9 of them because some parts become obsolete. I bought two boards (#6 and #7) from him for exhibition purposes. With the creation of the MEGA65 this has delayed but will be realized in a much bigger scale as they now became part of another story. Well, to be correct, *prototype II* has already been displayed as a C65 without anybody noticing (not even the C65 owners hehe).

    I believe Paul also received a board from Wayne. At a later point we would like to try to replace the missing custom chips by small FPGAs with adapters to make the boards usable.

    So, *prototype II*: Case remade from scratch (as close as possible to the original) by MEGA, Wayne's replica mainboard inside, keyboard from Commodore (Mitsumi) early 1990s.

    Next and hopefully final *prototype III*: Case with new ports by MEGA,prototype mainboard by MEGA, protoype keyboard made by MEGA. Expect this around _October_.

    best
    Deft

    :: @Deft added on 08 Jul ’16 · 15:17

    ps: Is it me or do markups behave strangely?

  • I'm Wayne. I apologize for being out of the scene for the past year or so. I had a very bad head injury that I was recovering from. Since then I've moved back to Minnesota (from Arizona) to be closer to family and friends while I put my life back together again. I think I'm back up to speed enough to get reacquainted with the C65 scene again. I still love this machine.

    I'm just a C65 enthusiast. I built the clone boards based on my revision 2A C65. My C65 is missing the VIC-III chip so I wanted a spare board or two that I could perform some experiments on while building my own VIC-III replacement without messing up my original. PCA Electronics used to manufacture the 15ns delay but it was obsoleted 20 years ago (similar story with the power filter). I talked them into making a few of them just for me but they were quite expensive. I thought it would be a fun easy project at first, but it took me the better part of a year to track down some of the components. Those KEL memory connectors are very hard to come by these days. And the 50 pin cartridge connector is next to impossible to find. All in all, I was able to completely populate 9 boards. I kept two for myself and sold most of the others. I still have one left for sale.

  • Hi Wayne,

    welcome and thanks for the introduction. While -as you know- I own two of your boards, it still would be nice to work on chip replacements, maybe using small FGPAs, to get your boards fully populated. However, I think you understand that building the MEGA65 is top priority to us, as it will not only look exactly like a C65, it will also be fully compatible and able to do a lot more. Maybe we will even settle with the holders of the Commodore brand, who knows :)

    All the others: Go and buy that last board from Wayne while you can, there will never ever again be such an opportunity. For us the boards were already extremely helful, since they are 100% exact replicas. Guess you now understand what's inside the MEGA65 prototype II shell? We wanted to be 100% authentic and afterwards slowly and carefully enhance stuff. Instead of doing all from scratch and losing authenticity.

    Once MEGA65 is finished there will be several exhibitions at our partner locations where we will show original C65s, Waynes boards, our first prototypes and of course the final machine.

  • It says on C64wiki, that Mega65 will have "Sound: Dual soft-SIDs + dual 8-bit DACs". Does this mean that it will be possible to play digital audio in Mega65? How about using the DMA chip to play digital sounds without using all the CPU cycles?

    It sure would be nice to have a mod player that could mix SID sounds and digital audio. :)

  • Just my personal opinion on this, if I am not boring enough already: I'm not sure if there will be DMA-like stuff for that. I also had that thought, but honestly, it's kinda interesting that it worth at all, if you have 50MHz CPU as well ... Just think about that, the famous GLX player on IBM XT @4.77MHz could achieve playing something like 20 channel module playback or so? :-O Yeah, I guess it used SoundBlaster's DMA anyway too, to play the mixed sample, but still, compare the raw CPU power then. What I found more useful is to have a FIFO so you can "inject" some amount of samples quickly (btw even using the DMAgic of M65 ...) and it can have a full/empty (and especially almost/half empty for example) signals. A dedicated sound DMA is - I guess - more complicated and maybe not so much 8 bit-ish already at all, if I can say that. Even this is a bit that. I guess M65 can happily use just an IRQ or something at the given sample rate to send data and still has enough CPU power left for the work. Some time ago I wrote an SD-card audio play running on 4MHz Z80 (and Z80 has worse IPC than 65xx CPUs) and it was capable to play at around 30KHz, still having enough CPU time to send control to the SD-card to read the next block to the play buffer. Surely, there you don't need to mix channels, processing module commands etc, but don't forget, that M65 CPU @ 50MHz is kinda fast (in fact it can emulate an intel 8080 just in software to be something like a ~12MHz 8080, what I did for some primitive software only CP/M emulator for M65). So in nutshell: I guess there is plenty of enough power in M65 to do mod playback without dedicated hw support too for sample blackback, but surely, some "cheats" (like the FIFO) can't hurt anyway :)

  • The MEGA65 currently indeed has two soft SIDs and a left and right digital audio channel. You can also set a register that tells the MEGA65 to talk to external SIDs on a cartridge. The mixing circuitry for the audio would be part of that cartridge (which doesn't yet exist).

    As for DMA or FIFO assistance for digital playback, this is of course quite feasible to do, and not that hard, but we haven't done it yet. Also, as LGB has said, at 50MHz, the cost of pushing a sample into the digital audio output lines, on every raster line if you so wish, is pretty cheap. That said, we will likely add at least some sort of digital audio FIFO.

    Paul.

  • Just a new thought here: I think, at least FIFO would be useful for one given purpose: using sole IRQ at the frequency of the playback rate is fine on a 50MHz CPU, right. However there is some problem if some would like to use DMA for whatever gfx trick for example (like fractional step to render "doom like corridor" or simply move memory areas etc) then DMA is "blocking" type on M65, so no CPU activity while DMA is working. Ergo, it's not possible to have playback during a DMA session as it blocks the execution of the CPU. However, if FIFO is "deep" enough, it can provide enough samples during a DMA transfer probably.

  • Yes, I know about the "INT" bit in DMA list entry description for sure, but it's unknown if it was ever supported by any actual C65, and AFAIK Mega65 does not support it currently (?? at least I don't emulate that in my Mega-65 software emulator). But about plans in this direction, Paul can say a lot mode than me, of course.

    :: @LGB added on 17 Jan ’18 · 09:11

    Please note, that c65manual.txt and similar files are hard to tell how accurate, often (even at F018 DMA controller description) it's stated that some things are different or even features not available at "initial versions". Moreover, I think, we know at least about two very incompatible F018 revisions, F018A and F018B even the DMA list length and the layout is different, and some known to be existing real C65 ROM images use on or the other only. Who knows, maybe even more variants, after all, existing C65s were only prototypes in various stage of the development in different state. But still, it's true, that besides this issue, there can be extension in Mega65, especially when it does not conflict with too much C65 software already exits, just because there are not so much of them :)

  • Yes... The M65 implementation is having to keep to the "spirit" of the C65 specification since it was incomplete.

    However, the potential for the feature is there and it certainly makes sense to implement it and I don't think it would be terribly difficult to do.

    I think to make using the DMAgic really useful to games and the like, implementing the INT bit feature is important. Otherwise, you're always going to be limited to terribly short DMAgic job runs and juggling them with your IRQ handler and raster timing is going to be a real pain.

    If its not implemented now, its certainly something people are going to ask for. I know I would want it.

    The idea is to actually finish the M65 implementation and "C65 compatibility" is really not something that should be particularly high on the "need to have" list. Like you said, there are quite significant differences between the revisions. Compatibility with them all is impossible. Existing C65 software (which there is very little of) can be easily patched and even has to be, just to run on a variety of C65s.

    Personally, I'd rather see a feature-rich M65 implementation that is incompatible with certain C65 revisions or even all of them if needs be, than one that is dumbed-down in order to try to be compatible with something that was never realised and barely used.

    The C65 as a working machine standard is a concept, not a reality at all. That's the truth. There is no such thing as "C65 compatible" and never will be.

  • I can't say I don't like your point, to be honest :) But I spoke about the current situation mode. I think too, INT feature can be useful. As so many other things too btw. The FIFO for audio playback is still nice that some can lower the interrupt rate, which can be quite problematic especially if some want to really "extract" even the "last cycle" of the 50MHz CPU as well. Or just for simplicity who knows. However so many things can be "great" :-O that's the only problem hre, I think.