[U-Boot-Users] RAM mapping repeats

Joao, Nuno (ext) nuno.joao-ext_nbs at siemens.com
Wed May 10 11:55:27 CEST 2006

> On Behalf Of Antonio Di Bacco
> Sent: terça-feira, 9 de Maio de 2006 21:49
> Subject: [U-Boot-Users] RAM mapping repeats

> I have 16MB of RAM (0x01000000) then I specified BR2=0x0000xxxx and 
> OR2=0xFE000000 . Obviously if I write at 1000000 is the same as I write at 
> 0x00000000. That is, the memory repeats in the space address. This doesn't 
> seem good to me because I will not receive any bus error if go to an address 
> higher than my RAM size. Am I wrong? 

	No, you are not wrong.
	You should set the CS address range only for the address range 
	supported by your device. If you setup a bigger address range in
	the CS, the wrap-around happens, it is "normal" because your device
	is "looking" only at the less significant 24 address lines. An
	address like 1000000 uses more than 24 address bits, so the extra
	bits will be ignored because they are not connnected to your device
	(this is simplistic view, assuming the device has an 8 bit port size).
	In your case you should set AM to 1111.1111.0000.0, check your
	device's datasheet.

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