[LinuxBIOS] RAM limit of TM5800 with VT8231 southbridge

Bari Ari bari at onelabs.com
Thu Nov 17 17:02:45 CET 2005

Miernik wrote:

> What are the real RAM limits? 

The "real" RAM size limit is a function of several aspects of the design.

	Design of the memory controller silicon
	PCB layout
	Number of DIMM memory slots
	Design and layout of the actual DIMM's

> The TM5800 CPU supports 4 GB of RAM, so

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 arranged as two banks of 512MB or four banks of 256MB.

What the maximum DRAM size is for the thin client design by HP depends 
on how they designed the PCB and BIOS.

> thats the upper limit, but is there anything that limits it lower, and
> if so what?

Design of the memory controller silicon and available DIMM 
configurations plus BIOS sets the lower limit.

The memory controller can handle devices as small as 4M x 16 and with 
one bank. Its lower limit then is 32MB.

> I am now planning to buy a 1 GB DDR SO-DIMM module, and I hope it'll
> work in the slot. Will it? Will only some modules work? If so what
> should I look for? Will this module work:
> http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=6821167601
> I found somewhere that:
> TM5800 memory subsystems can be populated with
> 64-Mbit (4M x 16 or 8M x 8),
> 128-Mbit (8M x 16 or 16M x 8),
> 256-Mbit (16M x 16 or 32M x 8), or
> 512-Mbit (32M x 16 or 64M x 8) devices.
> Note that only x8 and x16 memory devices are supported.
> Does it mean that if only my module is made of 32Mx16 or 64Mx8 chips,
> it'll work? Or is there anything more required? Does the VIA VT8231 or
> the thing's BIOS creates any more limits? With LinuxBIOS will I be able
> to put more RAM in than with stock BIOS?
> And finally is there anyone here who uses LinuxBIOS on such CPU and
> southbridge, and can share some expirience?

Look for modules that that minimize the number of loads. Use
the largest capacity devices possible for a given memory size. The SDRAM 
interface cannot drive more than sixteen unbuffered devices. SDR SDRAM 
configurations requiring more than sixteen loads must use buffered SDR 


More information about the coreboot mailing list