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Old 11 November 2017, 23:53   #1
E-Penguin
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Slow ram on an A500plus / hacking the ram68k

I've just received an A500plus and a ram68k 8mb fast ram thing that plugs into the processor socket. All good.

http://www.mkl211015.altervista.org/ram68k/

However... I would rather have it configured as 4mb fast + 1.5mb slow to aid game compatibility. The project upon which the ram68k is based had this option but is not available. But it must be possible.

The source for the cpld is available and there are code comments indicating how to turn it into a 4mb fast. I just need to work out how to put some of the rest into the $C0,000 space but I guess that's just modifying the MUX.

What I can't find is any information on how the Amiga finds the slow memory. I don't think it's autoconfig, but is there something else?

Has anyone done similar?
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Old 12 November 2017, 00:31   #2
robinsonb5
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I think the Amiga detects slow RAM the same way it detects Chip RAM - throwing data at it and seeing if it sticks.
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Old 12 November 2017, 11:00   #3
nogginthenog
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Indeed:

http://wandel.ca/homepage/execdis/exec_disassembly.txt
Code:
        ; Now go and check for memory in the $C00000 - $DC0000 area.
        ; This allows for a maximum of 1.75 megabytes of non-chip memory
        ; to be automatically configured if located at $C00000.
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Old 12 November 2017, 11:13   #4
E-Penguin
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So just updating the autoconfig to report 4mb and updating the MUX to respond to C0,000 ought to do it? I'll give it a go. Presumably I can't break anything if I get it wrong!
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Old 12 November 2017, 17:38   #5
robinsonb5
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Quote:
Originally Posted by E-Penguin View Post
So just updating the autoconfig to report 4mb and updating the MUX to respond to C0,000 ought to do it? I'll give it a go. Presumably I can't break anything if I get it wrong!
That should do it - just make sure the MUX doesn't respond beyond DC0000 or you'll clash with the custom chips </captain obvious>
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Old 12 November 2017, 19:40   #6
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I thought I might play it safe (I've not done HDL before) and just do 1mb at C0,000 (a simple check on 1100,xxxx(bin) on the address line).
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Old 13 November 2017, 01:06   #7
robinsonb5
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Quote:
Originally Posted by E-Penguin View Post
I thought I might play it safe (I've not done HDL before) and just do 1mb at C0,000 (a simple check on 1100,xxxx(bin) on the address line).
Good plan - it'll be interesting to see how it works out. Good luck!
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Old 16 February 2018, 12:10   #8
kgc210
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How did you get on with this?
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Old 11 December 2018, 00:06   #9
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Sorry, just noticed your question. The short answer is that I gave up as it was a bit beyond me
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Old 11 December 2018, 19:09   #10
hlide
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http://www.mkl211015.altervista.org/ram68k/

I was looking for that kind of board to add 8MB fast RAM. I already have an external card which allows for my A500+ to get 2MB chip RAM (from the boobip card) and 1MB slow RAM (from the motherboard). I would be interested to see if I can slot this board to add 8MB fast RAM then the CPU riser to slot a 68030TK board without the 4MB SRAM board (in case the latter resides in the same area than the 8MB).

I know. I like to experiment a Frankenstein's creature!
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