[U-Boot-Users] porting to custom at 91 board

[Wolfgang Denk]

In message <1101030722.6343.6.camel at localhost> you wrote:
>
> > Instead of doing all  this  which  is  really  non-trivial  and  also
> > ineffficient you could just boot from flash. I've just checked in the
> > necessary patches for the AT91RM9200DK and CMC_PU2 boards ...
> 
> What do you mean by booting from flash? Since I've got only an SPI flash

I mean booting from the  NOR  flash  attached  to  any  halfway  sane
design.

> connected, U-boot has to be taken apart, since the AT91 internal boot
> loader can only load 16KB of code from the flash into the internal
> processor SRAM. So what is needed is some code for the SPI flash, which

No - you are not restricted to booting from SPI DataFlash,  and  it's
not 16 kB. The AT91RM9200 supports 3 boot methods:

1) Pulling the first 12 kilobytes of a SPI DataFlash memory part into
   internal SRAM and executing it.

2) If #1 fails, pulling the first 12 kilobytes of a serial I2C EEPROM
   into internal SRAM and executing it.

3) If #2 fails, executing code from an attached NOR flash device.

What we use is 3) as there is NOR flash on both the AT91RM9200DK  and
the CMC_PU2 boards, so this is the fastest way to boot a system.


If you don't have any nor flash, you  should  (1)  complain  at  your
hardware designers and (2) make sure that CONFIG_BOOTBINFUNC is _not_
defned in your board config file.

> boots the processor, and reads the rest of u-boot from the SPI flash
> into the initialized SDRAM.
> 
> Does booting from flash solve the SDRAM initialization problem? (I mean

Yes, of course, because you can include regular  initialization  code
for the memory controller.


Best regards,

Wolfgang Denk

-- 
Software Engineering:  Embedded and Realtime Systems,  Embedded Linux
Phone: (+49)-8142-66989-10 Fax: (+49)-8142-66989-80 Email: wd at denx.de
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