Mapping memory

[MartinW]

Are there any limits as to the size of memory chunks that are defined in Amiga's? I probably don't really mean limits because obviously there are limits, I thin I mean advantages or disadvantages to certain sizes?

The reason that I ask is that my accelerator's ram is defined as:

32bit address space
0x08000000 - 32MB
0x0A000000 - 32MB

I'm curious as to why two blocks of 32MB rather than one of 64MB?

In actual fact, my card has 128MB rather than 64MB. I had been adding the additional 64MB at 0xC0000000 using AddMem in MMU config. I don't have the source for the boot loader but I've hacked it to change it from two 32MB blocks to two 64MB blocks. It seems to work fine, but is there any reason that this is a bad idea or won't work?

I now have:

32bit address space
0x08000000 - 64MB
0x0C000000 - 64MB

The only thing I'm struggling with at the moment is that "SYSINFO" and "Which Amiga" both report the new values, "Show Config" is showing the new addresses but the old sizes. I'm still trying to work that one out!

[nogginthenog]

There shouldn't be a practical limit. Well probably 2Gb.
Did you try the mergemem utility on Aminet?

(Was mergemem supplied with the OS at some point?)

[demoniac]

Originally Posted by MartinW

The reason that I ask is that my accelerator's ram is defined as:

32bit address space
0x08000000 - 32MB
0x0A000000 - 32MB

I'm curious as to why two blocks of 32MB rather than one of 64MB?

Most likely the memory decoder chip decodes to 5-bits instead of 6-bits.

Originally Posted by MartinW

In actual fact, my card has 128MB rather than 64MB. I had been adding the additional 64MB at 0xC0000000 using AddMem in MMU config. I don't have the source for the boot loader but I've hacked it to change it from two 32MB blocks to two 64MB blocks. It seems to work fine, but is there any reason that this is a bad idea or won't work?

If all the specs are the same between 32MB and 64MB memory, then you shouldn't have any problems.

[MartinW]

I would need to go back through all the threads from back when the parts were being ordered and the cards being built to find the exact specs but I think it was just a case of the design supporting 16MB ICs (x4) or 32MB ICs so obviously most of us on that particular order went with the bigger ones

[EDIT] Actually it may have been that v1 was 64MB, v2 was 128MB - I don't know. I know the CPLD controlling access to the RAM was updated for 128MB but not the boot rom (that I am aware of anyway). Hence I figured I'd patch my own.

Everything seems to be functioning OK with the new config. I was getting some strange slow down and lock-ups in Pinball Fantasies just now but I don't recall if that happened before, plus I'm not sure what the amount of RAM would have to do with that? I can easily go back to the old boot flash and 64MB ram to verify.

I didn't consider anything like mergemem (I didn't know about it for starters). My goal here really was to get everything setup in the boot flash. I have no idea if it makes the remotest bit of difference but it just seems tidier to me.