[LinuxBIOS] RAM limit of TM5800 with VT8231 southbridge

Bari Ari bari at onelabs.com
Fri Nov 18 17:20:58 CET 2005

Miernik wrote:
> Bari Ari <bari at onelabs.com> wrote:
>>The TM5800 can directly address 4GB of memory space since it is a 32 bit 
>>cpu. However the maximum memory size in the DIMM sockets the TM5800 can 
>>address is 1025MB 
> 1024 MB you mean?
Yes 1024MB, pardon the typo.
> If only 1 GB can go in DIMM sockets, where can the remaining 3 GB go?
Nowhere. All the DDR memory controller in the TM5800 can address is 1GB 
of DDR.

Look at Table #4, page 23, and section 1.2 on page 20, and through 1.2.4 
on page 24, TM5800v2.1_databook for an explanation of all this.
> Is the memory controller silicon inside the TM5800, or is it some
> separate chip?
Inside the TM5800. Figure #1, page 10, TM5800v2.1_databook.
>>Look for modules that that minimize the number of loads. 
> What are "loads"?
  Loads = devices.

Again, the datasheet may list capabilities that may not be available on 
the mainboard. There may be traces and pads on the board without 
components soldered in to save costs. The bean counters may drop 
features off a board after the design has been completed. Leaving out 
components such as DIMMs or other connectors is an easy way to save on 
production costs without having to respin the pcb.

The PCB designers may have had problems with traces and parts placement 
so memory speeds are compromised. Also the datasheet may not list all 
the problems and workarounds with the device. Issues with cpu's and 
chipsets are usually in the NDA doc's vs public doc's.


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