[U-Boot-Users] How to Handel Non-Continuous Memory Regions

[Jerry Van Baren <gerald.vanbaren@ge.com>]

Stuart Wood wrote:
> Wolfgamg
> 
> 
>> What has the MMU to do with it?
>>
>> Just program your memory controller such that the 4 banks form a
>> contiguous region.
> 
> The memory controller unfortunatly can  not map the SDRAM banks as
> contiguous region. That IS the main problem. For the SDRAM I'm using
> It ends up giving me region sizes of 8MBytes.
> 
> U-Boot runs in the first region, and we down load into the second region.
> If the down load is larger than the region size it gets corrupted.

IOW, your hardware sucks.  Not the first time *that* has happened.

> So the thought is to enable the MMU to do the address translation.
> Or is there another way to handle this?

No.

Wait, there is half a way.  If your SDRAM banks are not fully decoded 
(and they most likely are *not*), if you use the address last "copy" of 
the first bank and the first "copy" of the second bank, you will have 
two bank's worth of contiguous memory.

> It appears to happen when the image size becomes larger then a bank of
>> SDRAM. I've got a 32 MByte SDRAM
>> that appears as 4 banks of 8 MBytes.
>> 
>> The system is using u-boot 1.1.3 and we will move to 1.3.3 soon.
>> The memory regions are broken up like this.
>> 
>> 0xE0000000 - 0xE07FFFFF
>> 0xE1000000 - 0xE17FFFFF
>> 0xE4000000 - 0xE47FFFFF
>> 0xE5000000 - 0xE57FFFFF

So you should be able to use
   0xE0800000..0xE0FFFFFF - 2nd "copy" of the first bank
   0xE1000000..0xE17FFFFF - 1st "copy" of the second bank
you will double your available consecutive memory.  You can do the same 
thing with the third and fourth banks of memory, but you will still have 
a gap between the first pair and second pair.  This will reduce your 
four fragments / three holes to two fragments / one hole.  Solved half 
your problem anyway.
   0xE4800000..0xE4FFFFFF - 2nd "copy" of the first bank
   0xE5000000..0xE57FFFFF - 1st "copy" of the second bank

HTH,
gvb