looking for some help understanding the following.  I have never hit such an error.  can someone provide general guidance on how to troubleshoot this? 
```DEBUG probe_rs::debug::unit_info: Found DIE, now checking for inlined functions: name=None
Frame 0: "HardFault handler. Cause: Escalated UsageFault (Undefined instruction)." @ 0x00061560
Frame 1: __udf @ 0x0005ed98 inline
       ./asm/lib.rs:48:1
Frame 2: __udf @ 0x000000000005ed98
       ./asm/lib.rs:51:17
Frame 3: <unknown function @ 0x0005587c> @ 0x0005587c
       /work/projects/caloo/app/src/modem.rs:92:1
Error: CPU halted unexpectedly
```