store program in external sdram

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Hi,

How do you store an entire program in external sdram, is it possible
to declare all sections in the linker script to sdram (eventually the
boot section to bram) ? Or is there another way to get all data in the
sdram ?

thanks

Tom

Re: store program in external sdram
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Which MCU, DSP, or CPU are you using?
Is it part of some other system, for example a Basic Stamp?

Most MCU's use external SDRAM for data storage not progam storage.
A lot of DSP's use external RAM for both data and program storage.
CPU's are pretty much all external RAM for both data and program space.




Re: store program in external sdram
I am using a memec development board (2vp4) with a virtex II pro fpga
with powerpc. On the board  32 Mb sdram is available. At this point we
use the bram to store our programs that's 64k. But what if we want to
implement an rtos ?

Tom

On Mon, 24 Nov 2003 06:59:13 -0600, "Earl Bollinger"

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Re: store program in external sdram
Sorry I don't know anything about that board. The www.memec.com website
wasn't working at this time either.
But usually, you have a ROM or flash ROM on board.
The RTOS and your programs are all stored in the ROM, during powerup, the
monitor program or loader program
executes the RTOS which in turn can auto run your first or primary program.
In some cases, the CPU runs everything out of RAM. So in that case, you need
some sort of loader program that can read the RTOS and other programs from
some other
source into RAM and then execute it. I see this in some DSP's, but they have
a bootloader program in ROM on the chip. The DSP then can be loaded with the
RTOS or programs to
run from the main system storing the programs.
Some of the boards I deal with have a bootloader program in the MCU/CPU, it
then reads in it's RTOS or OS from a flash card into RAM and executes it.
Some other boards have on board flash and they run the RTOS directly out of
the flash, using the RAM for variable and data storage.





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Re: store program in external sdram
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Atmels Linux port does just that, so I assume that this is pretty standard
for Embedded (ARM) Linux.

At boot, the internal BootROM looks for the second level  boot.
This is linked to internal SRAM; and is loaded by the RomBoot from the SPI
Dataflash.
After loading the CPU jumps to the SRAM address 0.

The third level boot (U-Boot) is linked to SRAM and loaded from SPI
dataflash by the second level boot.
U-Boot is compressed, so the image is decompressed in the process.

U-Boot will run the "bootcmd" script which loads Linux from SPI Dataflash
to SDRAM and decompresses the kernel and the RAMDrive.
Both the Kernel and the RAMdrive are linked to SDRAM.

So in order to do what you want, you need to have one or more levels of boot
which are executed to load your SDRAM image.
--
Best Regards
Ulf at atmel dot com
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