The top-level Undefined Instruction handler TLUndef_Handler() saves the processor state, calls an appropriate second-level handler, and then restores the saved state. There are separate second-level handlers for each coprocessor and for each type of undefined instruction.

The VFP second-level handler VFP_Undef_Handler() first checks the VFP is enabled and the exception was not caused by an illegal instruction. If either check fails the handler calls Undef_Coproc_Handler() to process the bounce.

Otherwise the handler reads exception information out of the coprocessor to construct a list of operations that must be processed in software, and resets the VFP coprocessor's exception mechanism. It then prepares arguments for a user-level exception handler which will process the instruction list, and returns control to the top-level handler.

The second-level handler returns to the top-level handler, where the application's context is restored.

The second-level handler might raise a user-level exception. The second-level VFP handler does this, and the top-level handler returns by transferring control and parameters to the user-level VFP handler instead of returning directly to the bounced instruction.

The user-level VFP handler processes bounced operations in the application's context using the VFP computation engine software provided.

As floating-point exceptions are encountered calls can be made to application trap handlers, as specified by ANSI / IEEE Std. 754-1985, IEEE Standard for Binary Floating-Point Arithmetic. The application trap handlers can either return substitute results, or abort processing with longjmp. The support code uses the floating-point trap handler mechanism in the ARM C library, as described in RVDS Compiler and Libraries Guide.

When all bounced operations have been processed the user-level exception handler returns to an address provided by the top-level Undefined Instruction handler. For imprecise exceptions this is the address of the instruction that bounced. For precise exceptions this is the address of the following instruction.