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Old 04 July 2013, 13:46   #1
nickynoo
 
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Breaking the 2MB Chip RAM limit

It is a well known fact that the Amiga has a limit of 2MB chip ram, but is there anyone out there that has managed to break that limit?

Last edited by nickynoo; 01 November 2013 at 09:10.
 
Old 04 July 2013, 14:06   #2
demolition
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If you have to ask, I'll say you're in over your head.
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Old 04 July 2013, 14:22   #3
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Hello, I know the Amiga has a limit of 2MB chip ram. I wish to increase this to a higher amount.

I need help knowing where to begin solving this problem and could do with some help.

Where do I start?
Pointers - also you need to find free (not used memory area) - FAST can be used but with some conditions.

Personally i see no point to extend CHIP over 2MB - new chipset should be capable address whole 32 bit address space and old cycles need to be hidden from new chip point of view (also i can imagine that video generated by 2MB chips will be available as overlay to new video and combined before outputting).
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Old 04 July 2013, 14:46   #4
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Personally i see no point to extend CHIP over 2MB
There probably is no point other than for the sake of doing it

I really appreciate the pointers too, thanks.
 
Old 04 July 2013, 15:11   #5
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You'd have to design a completely new set of custom chips and add extra address lines..
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Old 04 July 2013, 19:48   #6
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Design a new Alice for the A4000, install an 8MB double sided SIMM to the chip ram slot, and set jumper J213 to 2-3 and J214 to 1-2 and tell us how it went.

Should be easy enough? ;-)
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Old 05 July 2013, 00:25   #7
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I was reading the FPGA arcade topic on amiga.org, the topic is very long and I cannot point to the exact posting but there was some conversation about this topic because the FPGA arcade can use a lot more chipmem.

And everybody thought it was a big deal and that compatibility will be broken if you created more than 2 MB chip, but in fact it was just one night programming by yaqube and most software is just oke with it.

"The 64 MB of DDR SDRAM is configured as 2 MB Chip, 1.5 MB Slow, 8 MB Fast and 48 MB of extra memory which can be used as additional Chip memory. You can have 50 MB of Chip RAM in total"

Doing it on a real amiga is another story, but still a interesting read.
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Old 05 July 2013, 00:27   #8
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"The 64 MB of DDR SDRAM is configured as 2 MB Chip, 1.5 MB Slow, 8 MB Fast and 48 MB of extra memory which can be used as additional Chip memory. You can have 50 MB of Chip RAM in total"
My maths might be rusty, but what happens with the other 4.5 MB?
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Old 05 July 2013, 00:56   #9
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Considering it's been done with the FPGA Arcade, I suppose it's possible..
And seeing how you can add a DKB MiniMegaChip (or whatever it's called) which contains an extra 1M of memory, I am thinking memory can be addressed there (directly to the Agnus?)..

So, is it possible to create a board that plugs into the Agnus socket and has memory and an FPGA which would emulate the Agnus, except for the modifications needed to address more memory???? (Taking the code from the FPGA Arcade??)

I'm not a hardware guy (OBVIOUSLY), but seems possible..

Of course, possible and realistically feasible are very different things...

desiv
(Although, if someone did come up with a new Agnus board with more memory that could plug into my A1200, I'd be sorely tempted to spend too much money on it...) ;-)
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Old 05 July 2013, 02:34   #10
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For what it is worth, I have a DraCo and it reports 4MB chipmem

Of course it is not an Amiga per se, but it runs AmigaOS without hiccups.
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Old 05 July 2013, 03:55   #11
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For what it is worth, I have a DraCo and it reports 4MB chipmem
Wow...
I wonder how they managed that..
Had no idea..
(I've heard of the Draco, but didn't know it has more CHIP!!)

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Old 05 July 2013, 04:11   #12
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I wonder how they managed that..
The DraCo doesn't have an Amiga chipset.
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Old 05 July 2013, 04:44   #13
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It has to have "a chipset" that addresses CHIP RAM.
Or else he wouldn't have seen 4M CHIP. ;-)

Therefor the solution might be similar...

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Old 05 July 2013, 05:19   #14
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and I need help with one too. I want sex and free beer.
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Old 05 July 2013, 05:28   #15
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I want sex and free beer.
Wait, so the beer needs to be free, but the sex you're willing to pay for?



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Old 05 July 2013, 06:28   #16
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What would the extra chip ram be used for?
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Old 05 July 2013, 06:47   #17
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What would the extra chip ram be used for?
More/bigger/better graphics and sound would be one of the advantages. Scanners for one on the Amiga are almost useless because of the lack of chipram.
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Old 05 July 2013, 08:07   #18
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More/bigger/better graphics and sound would be one of the advantages. Scanners for one on the Amiga are almost useless because of the lack of chipram.
Don't Forget sounds.
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Old 05 July 2013, 08:15   #19
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You'd have to design a completely new set of custom chips and add extra address lines..
It might be possible to use a bank switching type system added on to the chipset.

I believe all register accesses are visible on the chip register address bus (RGA). It might be possible to determine what DMA is occurring and bank switch based on this information. Each DMA channel would then have it's own 2MB space.

A clever design might let the CPU access a bank as fast ram when no other DMA was going on in that bank.
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Old 05 July 2013, 12:41   #20
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"The 64 MB of DDR SDRAM is configured as 2 MB Chip, 1.5 MB Slow, 8 MB Fast and 48 MB of extra memory which can be used as additional Chip memory. You can have 50 MB of Chip RAM in total"

Doing it on a real amiga is another story, but still a interesting read.
This is not a problem - if you have memory fast enough to hide OCS/ECS/AGA access cycle then there will be no (almost) difference between FAST and CHIP and whole addressed memory can be CHIP type.
I can imagine DDR SDRAM where using 32 or 64 bit word, burst mode, interleaving - CHIP RAM access can use only small fraction of bandwidth (especially with prefetch).
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