Debugging flash erase diriver caused the debugging session to disconnect

platform：CM0+
Adapter：ULINK2 and DAPLink
This exception only occurs when debugging using DAPLink, Using ULINK does not fail. A timeout occurred that caused an exception

DAPLink Log：
17:26:39:599 (24/12/2020) - READ MEM Access, AP 0, Addr 0xE000EDF0, Val 0x01000001, "DAP Read Memory (32 bit) - Success" - ID 237
17:26:39:651 (24/12/2020) - READ MEM Access, AP 0, Addr 0xE000EDF0, Val 0x01000001, "DAP Read Memory (32 bit) - Success" - ID 238
17:26:39:703 (24/12/2020) - READ MEM Access, AP 0, Addr 0xE000EDF0, Val 0x01000001, "DAP Read Memory (32 bit) - Success" - ID 239
17:26:39:756 (24/12/2020) - READ MEM Access, AP 0, Addr 0xE000EDF0, Val 0x01000001, "DAP Read Memory (32 bit) - Success" - ID 240
17:26:39:813 (24/12/2020) - READ MEM Access, AP 0, Addr 0xE000EDF0, Val 0xFFFFFFFF, "DAP Read Memory (32 bit) - FAILED" - ID 241
17:26:39:818 (24/12/2020) - READ MEM Access, AP 0, Addr 0xE000EDF0, Val 0xFFFFFFFF, "DAP Read Memory (32 bit) - FAILED" - ID 242
17:26:39:824 (24/12/2020) - READ AP Access, AP 0, Addr 0x00000000, Val 0xFFFFFFFF, "DAP Read AP - FAILED" - ID 243
17:26:39:826 (24/12/2020) - READ DP Access, Addr 0x00000004, Val 0xF0000000, "DAP Read DP - Success" - ID 244
17:26:39:894 (24/12/2020) - WRITE DP Access, Addr 0x00000008, Val 0x00000000, "DAP Write DP - Success" - ID 245

ULINK2 debug log：
17:27:46:501 (24/12/2020) - READ MEM Access, AP 0, Addr 0xE000EDF0, Val 0x01000001, "SWD Read Memory (32 bit) - Success" - ID 349
17:27:46:554 (24/12/2020) - READ MEM Access, AP 0, Addr 0xE000EDF0, Val 0x01000001, "SWD Read Memory (32 bit) - Success" - ID 350
17:27:46:607 (24/12/2020) - READ MEM Access, AP 0, Addr 0xE000EDF0, Val 0x01000001, "SWD Read Memory (32 bit) - Success" - ID 351
17:27:46:659 (24/12/2020) - READ MEM Access, AP 0, Addr 0xE000EDF0, Val 0x01000001, "SWD Read Memory (32 bit) - Success" - ID 352

Start by reproducing the flash-erase debugging failure on a CM0+ target with DAPLink and ULINK2, comparing the supplied DAPLink and ULINK2 logs around reads of 0xE000EDF0. Trace the timeout and failed access that disconnects the DAPLink session; done means flash erase completes without a debugging-session disconnect and the equivalent ULINK behavior remains intact.

Written by the indexing model from the issue text.