[LinuxBIOS] Ram limit at 128mb Bios, or hardware?

[Adam Talbot]

I have a small geode board that has a ram limit of 128MB.  This is 
stated in the doc's, I have not yet been able to test this, yet. If it 
does cap out at 128mb would this be a factor of the bios or the 
hardware, or both?
-Adam Talbot

[Richard Smith]

> I have a small geode board that has a ram limit of 128MB.  This is
> stated in the doc's, I have not yet been able to test this, yet. If it
> does cap out at 128mb would this be a factor of the bios or the
> hardware, or both?

In general is a hardware limit.  The ram interface is going to be
designed with a specific range of sdram chip density and bus loading
in mind.  At a given density you have to add more chips to the bus to
get more ram. This will increase the bus loading.  The limit should be
set for the maximim loading of the highest density at the maximum
speed.

If you purchase high quality ram modules that don't load the bus as
much and have very good matching on pcb you *might* get away with
adding more than the said maximum.  Also If you slow the bus down you
might be able to push the specs.  Over clockers do the inverse of this
all the time.  Getting good quality ram (keeping it good and cold) and
upping the clock rate beyond rated specs.

Density wise you can't normally do a whole lot.  Usually that needs a
new sdram controller.

As with all things in semi-conductors you can probally push the specs
beyond whats on the datasheet but it may not work across all boards.

[Bari Ari]

Yes  :)

If it only has one DRAM slot it's probably a limitation of the pcb 
layout and or DRAM controller.

Which geode board or which chipset is being used? I can check the 
hardware specs for you.

-Bari

Adam Talbot wrote:
> I have a small geode board that has a ram limit of 128MB.  This is 
> stated in the doc's, I have not yet been able to test this, yet. If it 
> does cap out at 128mb would this be a factor of the bios or the 
> hardware, or both?
> -Adam Talbot

[Adam Talbot]

Thank you for the great info Richard.  Bari here is all the current info 
I have on the board.
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&ssPageName=ADME:B:EOIBSAA:...
I hope to get to play with it soon.
-Adam

Bari Ari wrote:
> Yes  :)
>
> If it only has one DRAM slot it's probably a limitation of the pcb 
> layout and or DRAM controller.
>
> Which geode board or which chipset is being used? I can check the 
> hardware specs for you.
>
> -Bari
>
> Adam Talbot wrote:
> > I have a small geode board that has a ram limit of 128MB.  This is 
> > stated in the doc's, I have not yet been able to test this, yet. If 
> > it does cap out at 128mb would this be a factor of the bios or the 
> > hardware, or both?
> > -Adam Talbot

[Richard Smith]

On 11/16/05, Adam Talbot  wrote:
> Thank you for the great info Richard.  Bari here is all the current info
> I have on the board.
> http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&ssPageName=ADME:B:EOIBSAA:...
> I hope to get to play with it soon.

In this case you limit is neither hardware or software.  It appears to
be cost.  They just didn't want  to spend the extra $$ to put a
additional SODIMM on there.  That or they just didn't have the board
space.  Board real estate is closely coupled to cost.

XpressRAM Subsystem

* SDRAM interface tightly coupled to CPU core and graphics
subsystem for maximum efficiency
    * 64-Bit wide memory bus
    * Support for:
          o Two 168-pin unbuffered DIMMs
          o Up to 16 simultaneously open banks
          o 16-byte reads (burst length of two)
          o Up to 256 MB total memory supported

[Richard Smith]

>       o 16-byte reads (burst length of two)
>       o Up to 256 MB total memory supported

Someone would have to study the datasheet to answer this but if it
somehow supports 256Mbit chips it might be possible to get a 256 Meg
stick in there.  Highly unlikely though.

[Bari Ari]

The GXLV processor on that board only supported up to 256MB of SDRAM. 
128MB per SDRAM slot.

-Bari

Adam Talbot wrote:
> Thank you for the great info Richard.  Bari here is all the current info 
> I have on the board.
> http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&ssPageName=ADME:B:EOIBSAA:...

[Adam Talbot]

Well... I have a 256mb (sdram sodimm pc100) sitting around, but it is of 
VERY low quality.  I will stick it on and hope for the best. If I 
remember from the last few times I have run across this issue, the board 
will still boot and run just fine, but it will only be able to access 
128mb of the 256mb stick. I think. I will let you guy's know how it 
turns out.
End the end I am looking only for one thing, boot time.  How fast can I 
get from power on to playing music in my embedded automotive application 
(Car computer). The less memory I have, the less I need to suspend to 
disk. I will give it a nice big swap space to play with.
-Adam

Richard Smith wrote:
> >      o 16-byte reads (burst length of two)
> >      o Up to 256 MB total memory supported
>
> Someone would have to study the datasheet to answer this but if it
> somehow supports 256Mbit chips it might be possible to get a 256 Meg
> stick in there.  Highly unlikely though.

[Bari Ari]

The old GX1 and GXLV's were sensitive to SDRAM SDCLK speeds vs the 
number of loads (devices). Validated memory timings were pretty 
conservative. Depending on how your 256MB SDRAM SODIMM is configured, it 
may need to have the SDCLK slowed to make the half that may be 
accessible by the memory controller to work reliably.

-Bari

Adam Talbot wrote:
> Well... I have a 256mb (sdram sodimm pc100) sitting around, but it is of 
> VERY low quality.  I will stick it on and hope for the best. If I 
> remember from the last few times I have run across this issue, the board 
> will still boot and run just fine, but it will only be able to access 
> 128mb of the 256mb stick. I think. I will let you guy's know how it 
> turns out.
> End the end I am looking only for one thing, boot time.  How fast can I 
> get from power on to playing music in my embedded automotive application 
> (Car computer). The less memory I have, the less I need to suspend to 
> disk. I will give it a nice big swap space to play with.
> -Adam
>
> Richard Smith wrote:
> > >     o 16-byte reads (burst length of two)
> > >     o Up to 256 MB total memory supported
> >
> > Someone would have to study the datasheet to answer this but if it
> > somehow supports 256Mbit chips it might be possible to get a 256 Meg
> > stick in there.  Highly unlikely though.