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@xxxxxxxxxxxxxx > [mailto:linux-mips-bounce@xxxxxxxxxxxxxx]On Behalf Of Wolfgang Denk > Sent: Thursday, October 06, 2005 12:29 AM > To: Arravind babu > Cc: linux-mips@xxxxxxxxxxxxxx > Subject: Re: Basic question w.r.t bootloader > > > In message > <20051006065332.6978.qmail@xxxxxxxxxxxxxxxxxxxxxxxxx> you wrote: > > > > 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@xxxxxxx > The IQ of the group is the lowest IQ of a member of the group divided > by the number of people in the group. > >
