It is likely that the "Undefined Instruction" been printed by ROM code. And ROM code should print "r14_undef" and followed with LR value which points the place where the exception occurred. Do you see these ever?
B.R
Jerry
Also, I've seen cases where 'Undefined Ins' was caused when the wrong toolchain was used: for example - using a toolchain for armv7 (mx6) to build code for arm926 (mx28). Make sure you have a suitable toolchain for mx28.
It is likely that the "Undefined Instruction" been printed by ROM code. And ROM code should print "r14_undef" and followed with LR value which points the place where the exception occurred. Do you see these ever?
B.R
Jerry
Please make sure you follow the procedures below:
http://git.denx.de/?p=u-boot.git;a=blob;f=doc/README.mxs;h=ed2e5688562ac1af55a7c6213f5f3eb825e055b8;...
and
http://git.denx.de/?p=u-boot.git;a=blob;f=board/freescale/mx28evk/README;h=958ebc679106a52810506c506...
Please take a look at this past thread, it might be able to help you: