UART handler mode issue

We are developing some applications based on the DSPS sample code. The firmware is loaded onto the DA14580 chip from an external M4 processor via UART. A few seconds later after the Dialog chip boots successfully, the M4 processor send some message through the UART, the DA14580 M0 processor immediately enters into the Handler Mode around address 0x00028158. The debugger cannot display what c code is running. It is running some instructions from Disassembly (see below). Is there anyway to figure out what is the code doing and why the processor enters into this handler mode? Thanks.

0x00028158 6B00 LDR r0, [r0, #0x30]
0x0002815A 4700 BX r0

0x0002815C B510 PUSH {r4,lr}SystemInit
0x0002815E 4822 LDR r0,[pc,#136] ; @0x000281E8
0x00028160 6881 LDR r1,[r0,#0x08]
0x00028162 0709 LSLS r1,r1,#28]
0x00028164 0F09 LSRS r1,r1,#28main
0 x00028166 2901 CMP r1,#0x0184] ; @0x20003A80
0x00028168 D01A BEQ 0x000281A0