[LinuxBIOS] RAM limit of TM5800 with VT8231 southbridge

Richard Smith smithbone at gmail.com
Sat Nov 19 17:23:36 CET 2005

> >
> > 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.

Processor address space != system memory.

Some of that 32-bit address space is reserved for =memory mapped PCI
devices, Some of it is allocated to your Graphics card RAM, Some of it
accesses the BIOS chip.

In the datasheets there should be a section called something like the
processory memory map or system memory map.

This section should outline what ranges of addresses are reserved for
what.  The board designers may also have special areas that are

> > What are "loads"?
>   Loads = devices.

Thats EE speak for how many devices you can control on a bus.  Heres a
really gross oversimplification way to think about it.  Consider the
water coming into your home or apartment.  Only so much water can make
it into your home via the incomming pipe.  Each time you turn on a tap
the flow rate of the water reduces.  So when the washing machine is
on, the dishwasher is on, and somebody flushes the poor soul in the
shower gets almost no water pressure.

Each one of those items is a "load."  Each system can only support so
many loads before one part of the system suffers or just dosen't work
at all.

> Again, the datasheet may list capabilities that may not be available on
> the mainboard. There may be traces and pads on the board without

Like Bari says,  A high speed memory system is a _really_ tricky thing
to get right.  In fact I'm somewhat amazed we get them to work at all.
 At 200 Mhz a clock dosen't look like a clock anymore.  And you
violate timing specs if things are just a few nano-seconds (10E-9)
If the manual lists things a certain way then in general thats the way
they need to be or your in for trouble.

Memory aside, I thought there were issues with the transmeta parts and
not enough documentation from transmeta?

Richard A. Smith

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