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Amiga computer related discussion => Amiga Hardware Issues and discussion => Topic started by: leofoe on February 26, 2006, 11:12:27 AM
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I have an A1000 with a trapdoor RAM-expansion and also a half meg extra RAM soldered on the existing chips. The latter is added with the AddMem program in the startup-sequence at location $80000-$FFFFF.
When I add an A590 HD with 2 meg of RAM, the system crashes when I use AddMem with the same memory location. So obviously, that's not right. The A1000's memory map:
$000000-$07FFFF Chip RAM
$080000-$1FFFFF Reserved
$200000-$9FFFFF Potential Fast-RAM
$A00000-$BEFFFF Reserved
$BFD000-$BFDF00 PIA B (even addresses)
$BFE001-$BFEF00 PIA C (odd addresses)
$C00000-$DFEFFF Reserved for expansion
$DFF000-$DFFFFF Custom chip registers
$E00000-$E7FFFF Reserved
$E80000-$EFFFFF Expansion ports
$F00000-$F7FFFF Reserved
$F80000-$FFFFFF System ROM
Can I use all RAM I have?
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I would've thought this is possible...
$80000 is just behind the 512 KB chip mem and the A590's RAM should start at $200000 - could you verify this?
If this is true, it must be some kind of ghosting problem: data written to $80000 gets also written to another location, e.g. $280000. To get rid of that you'd have to analyse (and modify) the hardware hack. Testing should be easy: don't Addmem the RAM and try writing to a memory location at its end. If that changes memory at a similar address on the 590, you're bust. Might even be a bug in the pre-Gary address decoder...
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leofoe wrote:
I have an A1000 with a trapdoor RAM-expansion and also a half meg extra RAM soldered on the existing chips. The latter is added with the AddMem program in the startup-sequence at location $80000-$FFFFF.
What Kickstart are you using?
I just looked at exec 1.2 (v33.192) and the chip mem routine in that will search for upto 2mb of chip mem, so if the hack is done right you should be seeing 1mb of chip mem without using AddMem.
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... and without actually making it chip mem. The old (8367?) Agnus can't use more than 512 KB as chip RAM, so Amy would crash very soon...
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Zac67 wrote:
I would've thought this is possible...
$80000 is just behind the 512 KB chip mem and the A590's RAM should start at $200000 - could you verify this?
How do I do that?
Doobrey wrote:
What Kickstart are you using?
Version 1.3
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Zac67 wrote:
... and without actually making it chip mem. The old (8367?) Agnus can't use more than 512 KB as chip RAM, so Amy would crash very soon...
True.. so I guess it begs the question of how the hack generates the RAS/CAS signals for the area passed to AddMem.
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leofoe wrote:
Zac67 wrote:
I would've thought this is possible...
$80000 is just behind the 512 KB chip mem and the A590's RAM should start at $200000 - could you verify this?
How do I do that?
ShowConfig or SysInfo will show the locations of all memory in the system.
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@Doobrey: it's a hack, so it uses Agnus as RAM controller (RAS/CAS generation & refresh), but augments the address decoding logic in such a way that a 2nd 512KB bank becomes accessible for the CPU. How exactly this is done might be the cause of the problem, e.g. when just A19 is used for bank switching.
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ShowConfig doesn't work under WB1.3.
I'll try SysInfo later.
Thanks.
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Results of SysInfo:
2 MEG 200000 - 3FFFFF
1/2 MEG 0 - 7E7FF
When I add 1 MEG at location 400000 AddMem says it's e bad location and won't do it.
If I add 1 MEG at location 300000 it will do it. But that can't be correct, can it?
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Probably there is some ghosting going on. Could you try:
- disconnect A590
- AddMem $180000-$1fffff
- see if it actually works / RAM test
Did you AddMem $300000-$3fffff with the A590 connected? (I don't think this is possible because of the way free mem is organized, but am not at all sure.)
Try this e.g. in Basic:
- connect A590
- don't Addmem
- peek($3fffff), note value
- poke something else to $0fffff
- peek again and compare value, if it's changed there is ghosting
- repeat with pokeing $0effff, $0dffff, ..., $08ffff
The best way to find out fore sure would be to open up amy and look what cable connections were added inside. To eliminate ghosting you'd have to modify the hack anyway...
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Zac67 wrote:
The best way to find out fore sure would be to open up amy and look what cable connections were added inside. To eliminate ghosting you'd have to modify the hack anyway...
You mean this? (http://home.wanadoo.nl/leof/A1000Mem.jpg)
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Yes, that's the RAS/CAS distribution to the RAM chips - but where do they come from?