topic DAP and TAP register documentation in LPC Microcontrollers

DAP and TAP register documentation

janpieterderuit — Mon, 04 May 2020 20:12:58 GMT

Hi,

I'm looking into unlocking a locked LPC5460x processor from PyOCD like the unlock command in the Segger J-link Commander does.

I followed pyOCD/security.md, and was able to access Access Point #2 over CMSIS-DAP with a locked processor.
However I can't find any information about the available registers in that Access Point (or about the registers from the default Access Point #0).

Where can I find this information, or information how to unlock the processor from a CMSIS-DAP debug probe?

Thanks in advance.

Jan Pieter de Ruiter

Re: DAP and TAP register documentation

Sebastian_Del_Rio — Fri, 08 May 2020 15:19:33 GMT

Hi Jan Pieter, I hope you're doing well!

J-Link commander actually supports the "unlock" command for the LPC5460x:

To use this command, you can program the J-Link firmware to your LPC5460x using the "program_JLINK.cmd" script included in the LPCScrypt toolset, which can be downloaded from here.

After the debug probe is programmed with the J-Link firmware, J-Link commander can send the "unlock LPC5460x" command, and your LPC should unlock.

Please let me know if you continue to have issues with this.

Take care, best regards,

Sebastian

Re: DAP and TAP register documentation

janpieterderuit — Thu, 28 May 2020 22:41:00 GMT

Hi Sebastian,

Thanks for your response.

I knew about the jlink software for the LPC boards, and it works fine indeed.

However, from the license of that software I get that you are only allowed to use it for the onboard processor, not for an external processor on our custom hardware.

I actually was able to monitor the SWD commands with a logicanalyzer, and found the needed registers that way.

But it would be nice if it was documented somehow, because now I have no idea what is actually going on.

Best regards,

Jan Pieter

Re: DAP and TAP register documentation

Sebastian_Del_Rio — Mon, 01 Jun 2020 18:11:56 GMT

Hi Jan Pieter,

Thank you for your feedback, we will take it into consideration!

Please let me know if you need any more information.

Take care, best regards,

Sebastian