@sancho119 No matter what I tried, I could not unlock the E73 with the STLink.
I had to buy a jlink clone, download a bunch of segger debugging tools, use the segger tools to override the lock flag. After that I could flash the bootloader.
#To share my experience with the nRF52832.
#I was unable to disable the read protection / flash lock with a BMP or ST-Link V2, but i was successful with a J-Link.
#When nRF52832 chip is read protected / locked, the first step is to try:
nrfjprog –recover -f nrf52
#This performs the same task as:
Jlink -if swd -device nrf52
J-Link>SWDWriteDP 1, 0x50000000
J-Link>SWDWriteDP 2, 0x01000000
J-Link>SWDWriteAP 1, 0x00000001
#Wait until AP 2 is 0, and the operation is complete
#If two successive reads from AP 3 produce 0, then 1 then protection is disabled
#Tested with JLink v6.20b