[U-Boot-Users] Question about U-Boot in general and the AT91RM9200 in particular

Andreas Schweigstill andreas at schweigstill.de
Thu Jan 4 16:37:07 CET 2007


Sascha Erlacher schrieb:
> this is not correct. As Wolfgang points out you can boot directly from NOR
>  flash.
> It depends on the BootModeSelect (BMS) pin state of the AT91RM9200.

Unfortunately due to errata #37 external NOR flash will be accessed with
zero waitstates, which gives an access time of 20ns, so very fast and
expensive memory has to be used. And there also shouldn't be used any
external address decoders or bus buffers.

So using a serial boot ROM (Dataflash or EEPROM) usually will be the
best solution. Even a very small EEPROM can be suitable because the
program just has to modify bus timing for chip select 0 and jump to the
"slow" parallel Flash memory.

With best regards

Dipl.-Phys. Andreas Schweigstill
Schweigstill IT | Embedded Systems
Schauenburgerstraße 116, D-24118 Kiel, Germany
Phone: (+49) 431 5606-435, Fax: (+49) 431 5606-436
Mobile: (+49) 171 6921973, Web: http://www.schweigstill.de/

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