[U-Boot] Imx51 processor hangs when we do an md 0xf0000000 (memory display) in u-boot

We're are using the Freescale release L2.6.31_MX51_SDK_0912_Image and it will do this on a Freescale Babbage board and our design. It also does the same thing in Linux when we mmap the address 0xf0000000 and try to read from it. It does not hang on the Redboot.bin image supplied with the Freescale SDK. The Redboot dump command displays some data. On the Freescale 3Stack board we get an illegal address error in Redboot, but it will hang in u-boot. We realize this is a reserved physical address but would hope that an error of some kind would occur rather than locking up the CPU. Could it be some sort of MMU initialization difference between Redboot and u-boot?

Thanks in advance.

Greg