If its a DRAM DIMM module then SW reads info
about that RAM via the SPD interface.
SPD = Serial Presence Detect 
This is typically an I2C interface so
SW can bit bang it. 

SPD provides more info than just size.
For example on some systems you need to
know the RAS/CAS params and various
wait state settings in order to program your
memory controller for optimal performance. 
This is how PCs are able to configure themselves 
to work with standard modules. For more info
checkout this site ...

http://www.pcguide.com/art/sdram.htm

For SRAMs the HW guys usually provide
some set of registers for SW to read 
info its needs like size. And sometimes
they don't so you have to use address
probing tricks as Wolfgang described. 

-earlm

-----Original Message-----
From: linux-mips-bounce@linux-mips.org
[mailto:linux-mips-bounce@linux-mips.org]On Behalf Of Wolfgang Denk
Sent: Thursday, October 06, 2005 12:29 AM
To: Arravind babu
Cc: linux-mips@linux-mips.org
Subject: Re: Basic question w.r.t bootloader 


In message 
[ref] you wrote:

quoted

       Generally how bootloader/bootflash code detects
the size of RAM on the board? Is it hardcoded some
where in the bootflash code or is it detected using
memory chips ?

One method is to probe addresses (at N, 2*N, 4*N etc. starting with a
resonable value of N like 1 MB) until probing fails. See for  example
common/memsize.c in the U-Boot sources.

Best regards,

Wolfgang Denk

-- 
Software Engineering:  Embedded and Realtime Systems,  Embedded Linux
Phone: (+49)-8142-66989-10 Fax: (+49)-8142-66989-80 Email: wd@denx.de
The IQ of the group is the lowest IQ of a member of the group divided
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