[U-Boot-Users] Re: Installing U-Boot on target via USB/serial using U-Boot commands

Andrey P. Vasilyev andrey_vasilyev at mail.ru
Mon Sep 26 19:21:29 CEST 2005

On Mon, Sep 26, 2005 at 09:24:39AM -0400, Jerry Van Baren wrote:
> It looks like this is a very simple loader.  It writes to SRAM _only_ 
> and then jumps to that program (JTAG loaders typically allow you to 
> write to flash, manipulate registers, and jump anywhere, single step, 
> etc.).  Theoretically you could load u-boot this way, but nobody has 
> volunteered that they have done it so you would likely be blazing a new 
> path.

No, it is an ordinary (and supported by Atmel) way to bootstrap an 
AT91RM9200 boards having only a simple COM-port cable :)

> My advice would be to write a simple "burn flash" routine (it can be 
> done in a couple dozen lines of assembly - don't get elaborate) ORGed at 
> the start of SRAM and prepend it to the u-boot image.  Your USB loader

Atmel have such a simple utility called RomBoot. It acts as a simple 
first-stage bootloader, and allows to set up SDRAM and PLLs, 
load U-Boot from DataFlash or (by X-Modem) from DBGU UART and passing 
control to it.

> (I'm guessing the target side looks like a simple usb-UART) would load 
> the burner utility and the u-boot image as a single lump and jump to the 
> burner utility.  The burner utility would program the u-boot image from 
> SRAM into flash.  Reset the board and you are off & running.
> If your first attempt doesn't work, you are in the "burn & learn" cycle. 
>  This can be successful if your image is close to working and you have 
> a fair amount of experience, or it can be an infinite time suck.  If the 
> latter is the case, a JTAG debugger is invaluable.

I'm using a simple jumper on the board for turning DataFlash chip into 
reset state while booting. This allows to boot from DBGU serial port 
when DataFlash contains a valid but non-working image.

With best regards,
  Andrey Vasilyev

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