REU for C-64 & C-128

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Nonefornow
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Re: REU for C-64 & C-128

Post by Nonefornow » Thu Apr 21, 2016 9:17 pm

eslapion wrote:I already own the IP for a static RAM based REU. You guys are tempting me for a kickstater.

A lot of money, energy and time needs to be invested to adapt this IP to an FPGA or CPLD, create the PCB and build this thing.

Who's in?
I would support such a kickstarter if the 16MB REU were to be compatible with the 1750 and usable in the C64, C128, and C128DCR. Also available under GEOS / Wheels / The Gateway / MP3.



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eslapion
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Re: REU for C-64 & C-128

Post by eslapion » Sun Apr 24, 2016 3:42 pm

Nonefornow wrote:I would support such a kickstarter if the 16MB REU were to be compatible with the 1750 and ...
Right off the bat, that's impossible. The 1750 used a controller which internally used a 24 bit addressing scheme but directly supported 512k at the most.

Any and all attempts at offering more than that resulted in software compatibility problems.

That's why I am very reluctant to engage in such a project. Too many people have too many unrealistic expectations because they don't know the technical details.

The REU built into the 1541 Ultimate I and 2 supports up to 16MB the correct way (unlike some mods for the 1750 which tries to "guess" the higher address bits) yet there are so many people who whine it has compatibility problems, isn't cycle exact, etc...

If you set the 1541U1/2 REU to 512k, you get the highest possible level of compatibility. If that's not good enough for you then nothing ever will be.
Wealth, like happiness, is never attained directly. It comes as a by-product of providing a useful service. -Harland D. Sanders

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Zippy Zapp
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Re: REU for C-64 & C-128

Post by Zippy Zapp » Mon Apr 25, 2016 3:41 pm

I don't pretend to know the technical details of more then 512k because I have only 2 REUs one is original 1764 256k and one is original 1764 that I recently added 256k to make it more or less a 1750. I didn't add the resistor that is missing on the 1764 but apparently it isn't critical. Anyway it is usable in everything that supports a REU as would be expected.

I understand that going beyond that and you will have problems unless something is designed specifically for it. So on a dedicated REU like this is it possible to have some sort of mode switch that allows 512k standard and then expanded 16MB REU mode or something like this, if you get what I mean? Then you could have the 1750 clone mode and still have access to the 16MB for whatever people use those for?
Commodore - Changing the world 8 bits at a time.

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Re: REU for C-64 & C-128

Post by Nonefornow » Mon Apr 25, 2016 7:09 pm

eslapion wrote:The 1750 used a controller which internally used a 24 bit addressing scheme but directly supported 512k at the most.
CMD released the 1750XL cartridge with 2MB. After that there was a mod to expand the Commodore 1750 REU to 2MB as well. I am not interested in modifying my 1750.
eslapion wrote:That's why I am very reluctant to engage in such a project. Too many people have too many unrealistic expectations because they don't know the technical details.
Have listed my requirements precisely to avoid a mismatch in expectations.
eslapion wrote:The REU built into the 1541 Ultimate I and 2 supports up to 16MB the correct way (unlike some mods for the 1750 which tries to "guess" the higher address bits) yet there are so many people who whine it has compatibility problems, isn't cycle exact, etc...


I am not sure what you mean by correctly. Also, it appears that the REU built in the 1541U-II has compatibility problems with the C128 and the C128DCR. I have not had a chance to fully test it though.
eslapion wrote:If you set the 1541U1/2 REU to 512k, you get the highest possible level of compatibility. If that's not good enough for you then nothing ever will be.
Software like Wheels and MegaPatch3 can take advantage of more than 512K.

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Re: REU for C-64 & C-128

Post by dudz » Wed Apr 27, 2016 1:12 am

The 1750 used a controller which internally used a 24 bit addressing scheme but directly supported 512k at the most.
thats not quite correct - the upper 5 bits dont exist in the REC either. All REU "hacks" to expand beyond the 512k add them with an external latch.
Any and all attempts at offering more than that resulted in software compatibility problems.
thats easy to fix though - just disconnect the latch (with a switch if you must) or pull down the upper address lines to 0. most software doesnt have a problem though
The REU built into the 1541 Ultimate I and 2 supports up to 16MB the correct way (unlike some mods for the 1750 which tries to "guess" the higher address bits)
thats not quite correct either - the correct way would be doing what the CMD REU-XL does. (and there is no "guessing" of adress bits happening in any case - the upper bits always come from the latch, its that simple)
yet there are so many people who whine it has compatibility problems, isn't cycle exact, etc...
its actually cycle exact (for the parts that matter anyway) - the bigger problem is that the register contents after a transfer are not always correct, which confuses some software. that would be rather easy to fix though if anyone actually cared about doing it.

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eslapion
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Re: REU for C-64 & C-128

Post by eslapion » Wed Apr 27, 2016 2:44 am

Zippy Zapp wrote:I don't pretend to know the technical details of more then 512k because I have only 2 REUs one is original 1764 256k and one is original 1764 that I recently added 256k to make it more or less a 1750.
The 1750 and 1764 actually use the same board and the same REC. Just add the missing DRAM chips to a 1764 and you have a 1750, complete with C128 compatibility.
dudz wrote:thats not quite correct either - the correct way would be doing what the CMD REU-XL does.
Some say that's the wrong way... I am not a "religious" type and don't want to have to deal with clan feuds...
Nonefornow wrote:Also, it appears that the REU built in the 1541U-II has compatibility problems with the C128 and the C128DCR.
The 1541U/U2 prevents the C128 from going into C128 mode. It also won't support 2MHz operation because of the hardware configuration. Technically speaking, you can force a C128 into 128 mode with a few tricks and as long as you remain in 1MHz mode, the REU will work.

However, if you were to program the VHDL of the REC into another type of FPGA and make sure the hardware supports both speeds, it would work well on a C128.

However, because of what's said above, I would NEVER make an REU of more than 512k. I would also strictly make it using static RAM to ensure ultra low power requirements.
Wealth, like happiness, is never attained directly. It comes as a by-product of providing a useful service. -Harland D. Sanders

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Re: REU for C-64 & C-128

Post by motrucker » Wed Apr 27, 2016 9:52 pm

Another 512 REU isn't any help. I can already buy these. Are we back to the 2Mb mod for the 17xx REU?
C-64, C-128, and Amiga A2000 user

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Re: REU for C-64 & C-128

Post by Nonefornow » Thu Apr 28, 2016 12:25 am

motrucker wrote:Another 512 REU isn't any help. I can already buy these.


I concur.
motrucker wrote:Are we back to the 2Mb mod for the 17xx REU?
It looks as if that's really the only available option.

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Re: REU for C-64 & C-128

Post by Zippy Zapp » Thu Apr 28, 2016 5:13 pm

I agree that a 16MB would be ideal but my point was to add a 512k switch or mode that allows the 64 to see it as a 1764/1750 for programs that only work with 256/512k.
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Re: REU for C-64 & C-128

Post by dudz » Thu May 05, 2016 5:37 pm

Some say that's the wrong way... I am not a "religious" type and don't want to have to deal with clan feuds...
its a simple matter of ensuring software compatibility (with software written for 512k units - which is the majority afterall). for devices like 1541u its no problem, since you can just switch it to 512k (and then it works as expected) - but with an expanded REU of fixed size it will matter... which is why the CMD did it for their 2MB REU as well.

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