Can't connect to my NRF52840 using a Pico W as a debugger with OpenOCD.

[Kasper Larsson-Skauli]

I have created a custom board with an NRF52840 on an Ebyte E73-2G4M08S1CX. I am trying to burn a bootloader to the chip using OpenOCD and a Raspberry PI Pico W as a debugger. But in OpenOCD I keep getting an error that it can't connect to the board: 

...

Info : SWCLK/TCK = 0 SWDIO/TMS = 0 TDI = 0 TDO = 0 nTRST = 0 nRESET = 0
Info : CMSIS-DAP: Interface ready
Info : clock speed 1000 kHz
Error: Error connecting DP: cannot read IDR

I have connected SWDCLK, SWDIO, GND, and VDD from the pico to the board, and I have checked that the connections are valid using a multimeter. I also use the latest Pico debugger firmware and OpenOCD version. Is the chip in a locked state? I know that there are a lot of things that could be the cause of the issue, but I hope someone has some insight into what the problem could be. 

[Kenneth]

Hi,

By default the chip will have access port protection enabled, so you need to execute an erase all, this is described here:
https://docs.nordicsemi.com/bundle/nwp_027/page/WP/nwp_027/nWP_027_protected.html 

Kenneth

[Kasper Larsson-Skauli]

I cannot seem to get the debugger to connect through the swd and swclk pins. It seems OpenOCD throws an error before I can send any command to the chip. Could this be because of the access port protection? Or is it more likely to be a problem with the hardware or debugger?