We have a custom board with nFR51422. Of the first 4 prototypes only one works correctly. This indicates that the PCB is ok. One difference is the chip marking. The working is nrf51422 QFAACO 1319AK and non working ones are all nrf51422 QFAACO 1306AD.
The non-working ones are partly functional in the sense: The flash programming works and verifies without reported problems and the Keil programmer finalizes programming with the message: application running. I can see that neither of the xtal clocks are starting.
Debugging in Keil fails: When breaking into the debugger R15(PC) is FFFFFFFE and the instructions are all MOVS R0,R0 all the way down. PC counter increments but stays doing MOVS R0,R0 instructions.
Breakpoint in arm_startup_nrf51.s in reset handler is never taken.
What could leave flash programming working but execution failing?
Any hints on what could be a possible reason are warmly received.
