The exact message I have is:
Fatal exception (0):
epc1=0x40210c54, epc2=0x00000000, epc3=0x00000000, excvaddr=0x00000000, depc=0x00000000
However, note that with my other softwre, the epc1 was always around 0x401000**, at an address that did not appear in the disasembled file. But in this sample code, the address 0x40210c54 is found.
Here is what the dissasembled looks like around that address (I enlighted it in bold), in case it help:
...
40210bbc <user_rf_cal_sector_set>:
40210bbc: e0c112 addi a1, a1, -32
40210bbf: 7109 s32i.n a0, a1, 28
40210bc1: 61f9 s32i.n a15, a1, 24
40210bc3: 20f110 or a15, a1, a1
40210bc6: fffa21 l32r a2, 40210bb0 <wpa_sm_disassociate+0x4>
40210bc9: c46001 l32r a0, 40201d4c <ieee80211_chan2ieee+0x44>
40210bcc: 0000c0 callx0 a0
40210bcf: 005005 call0 402110d0 <system_get_flash_size_map>
40210bd2: 1f29 s32i.n a2, a15, 4
40210bd4: 020c movi.n a2, 0
40210bd6: 0f29 s32i.n a2, a15, 0
40210bd8: 1f28 l32i.n a2, a15, 4
40210bda: 4e92f6 bgeui a2, 10, 40210c2c <user_rf_cal_sector_set+0x70>
40210bdd: 1f28 l32i.n a2, a15, 4
40210bdf: 1132e0 slli a3, a2, 2
40210be2: fff421 l32r a2, 40210bb4 <wpa_sm_disassociate+0x8>
40210be5: 232a add.n a2, a3, a2
40210be7: 0228 l32i.n a2, a2, 0
40210be9: 0002a0 jx a2
40210bec: 7ba022 movi a2, 123
40210bef: 0f29 s32i.n a2, a15, 0
40210bf1: 000f46 j 40210c32 <user_rf_cal_sector_set+0x76>
40210bf4: fba022 movi a2, 251
40210bf7: 0f29 s32i.n a2, a15, 0
40210bf9: 000d46 j 40210c32 <user_rf_cal_sector_set+0x76>
40210bfc: fba122 movi a2, 0x1fb
40210bff: 0f29 s32i.n a2, a15, 0
40210c01: 000b46 j 40210c32 <user_rf_cal_sector_set+0x76>
40210c04: fba122 movi a2, 0x1fb
40210c07: 0f29 s32i.n a2, a15, 0
40210c09: 000946 j 40210c32 <user_rf_cal_sector_set+0x76>
40210c0c: fba322 movi a2, 0x3fb
40210c0f: 0f29 s32i.n a2, a15, 0
40210c11: 000746 j 40210c32 <user_rf_cal_sector_set+0x76>
40210c14: fba322 movi a2, 0x3fb
40210c17: 0f29 s32i.n a2, a15, 0
40210c19: 000546 j 40210c32 <user_rf_cal_sector_set+0x76>
40210c1c: fba722 movi a2, 0x7fb
40210c1f: 0f29 s32i.n a2, a15, 0
40210c21: 000346 j 40210c32 <user_rf_cal_sector_set+0x76>
40210c24: ffe521 l32r a2, 40210bb8 <wpa_sm_disassociate+0xc>
40210c27: 0f29 s32i.n a2, a15, 0
40210c29: 000146 j 40210c32 <user_rf_cal_sector_set+0x76>
40210c2c: 020c movi.n a2, 0
40210c2e: 0f29 s32i.n a2, a15, 0
40210c30: f03d nop.n
40210c32: 0f28 l32i.n a2, a15, 0
40210c34: 0f1d mov.n a1, a15
40210c36: 7108 l32i.n a0, a1, 28
40210c38: 61f8 l32i.n a15, a1, 24
40210c3a: 20c112 addi a1, a1, 32
40210c3d: f00d ret.n
40210c3f: 800000 add a0, a0, a0
40210c42: fe .byte 0xfe
40210c43: 3f .byte 0x3f
[b]
40210c44 <system_set_os_print>:[/b]
[b]40210c44[/b]: ffff31 l32r a3, 40210c40 <user_rf_cal_sector_set+0x84>
40210c47: 140c movi.n a4, 1
40210c49: 932420 movnez a2, a4, a2
40210c4c: 004322 s8i a2, a3, 0
40210c4f: f00d ret.n
40210c51: 000000 ill
40210c54 <system_get_os_print>:
40210c54: fffb21 l32r a2, 40210c40 <user_rf_cal_sector_set+0x84>
40210c57: 000222 l8ui a2, a2, 0
40210c5a: f00d ret.n
40210c5c: fe86e4 excw
40210c5f: 3f .byte 0x3f
40210c60: 210d30 srai a0, a3, 13
40210c63: fff040 excw
40210c66: 9c4022 s8i a2, a0, 156
40210c69: 3ffe87 bbsi a14, 24, 40210cac <system_get_os_print+0x58>
40210c6c: f0c112 addi a1, a1, -16
40210c6f: 0261c2 s32i a12, a1, 8
40210c72: 0129 s32i.n a2, a1, 0
40210c74: 1109 s32i.n a0, a1, 4
...