3.6.8. Undefined instruction

When ARM720T comes across an instruction which it cannot handle, it takes the undefined instruction trap. This mechanism may be used to extend either the THUMB or ARM instruction set by software emulation.

After emulating the failed instruction, the trap handler should execute the following irrespective of the state (ARM or THUMB):

MOVS PC, R14_und

This restores the CPSR and returns to the instruction following the undefined instruction.

Copyright © 1997, 1998 ARM Limited. All rights reserved.DDI 0087E