[U-Boot] About mtest on boot

Hello,

I want to stop autoboot and use mtest to check if my ram is alright, but 0x07FD2C00 forward freezes, and 0x00000902 also freezes, mtest, when using it. My ramsize is 0x08000000.

Does u-boot uses any parts of ram by itself, I mean, is there any known spots where I can't test because it would crash my system?

Thanks

Érico V. Porto