Reset over CTRL-AP

RE: Reset over CTRL-AP

Vidar Berg — Mon, 24 Nov 2025 14:57:53 GMT

Good to hear. Yes, it should be sufficient to reset the chip through the CTRL-AP

RE: Reset over CTRL-AP

Glenn Andrews — Fri, 21 Nov 2025 16:56:26 GMT

I think that should do it.

To be honest I'm not sure if being held in reset is even required.

Our main goal is to be able to erase and reprogram the nRF over SWD and restart it without needing the nRESET line wired up.

If we can do that, I think anything else is a bonus.

RE: Reset over CTRL-AP

Vidar Berg — Fri, 21 Nov 2025 12:40:25 GMT

No problem. I realize now I didn’t take this requirement into account when I answered earlier, and unfortunately I don’t see a way to do this through the CTRL-AP. However, would it be sufficient to keep the CPU halted after the firmware is programmed?

https://developer.arm.com/documentation/ddi0413/d/debug/debug-control/debug-halting-control-and-status-register

RE: Reset over CTRL-AP

Glenn Andrews — Thu, 20 Nov 2025 23:21:27 GMT

Sorry for the delay before reopening this.

I ran the commands on our nRF54L15 project board.

SWDWriteAP 0 0x0 did reset the board, but I was expecting SWDWriteAP 0 0x4 to hold the board in reset until it was released.

Is there a command that does that?

RE: Reset over CTRL-AP

Glenn Andrews — Tue, 28 Oct 2025 15:58:27 GMT

That's what I thought. Thank you for the quick response!

RE: Reset over CTRL-AP

Vidar Berg — Tue, 28 Oct 2025 11:43:20 GMT

Hello Glenn,

Yes, it’s possible to perform a “pinreset” via the CTRL-AP without physically asserting the pinreset input on the chip. Below are the commands I used when testing this here with J-Link Commander (JLinkExe/jlink.exe):

/* Use SWD */
SWDSelect
/* Power on debug interface by setting CSYSPWRUPREQ bits */ 
/* https://developer.arm.com/documentation/ihi0031/a/Debug-Port-Registers/Debug-Port--DP--register-descriptions/The-Control-Status-Register--CTRL-STAT */
SWDWriteDP 1 0x50000000
/* Select CTRL-AP (APSEL = 2) */
/* https://developer.arm.com/documentation/ihi0031/a/Debug-Port-Registers/Debug-Port--DP--register-descriptions/The-AP-Select-Register--SELECT */
/* https://docs.nordicsemi.com/bundle/nan_047/page/APP/nan_production_programming/nRF54L/nrf54l_select_access_port.html */
SWDWriteDP 2 0x2000000 
/* Pinreset */
SWDWriteAP 0 0x4
/* Release the RESET register value */ 
SWDWriteAP 0 0x0

(Ref. https://docs.nordicsemi.com/bundle/ps_nrf54L15/page/chapters/power-and-clock/reset/doc/reset.html#ariaid-title11)

[quote user=""]I saw in one answer a recommendation for 1MOhm pull-downs on the SWD lines, or is that for a different family?[/quote]

This is not needed or recommended on the nRF54L. The internal pull up is sufficient.

Best regards,

Vidar