nRF52840 JTAG disable and don't recover through any JTAG Debugger.

RE: nRF52840 JTAG disable and don't recover through any JTAG Debugger.

Amanda Hsieh — Mon, 14 Feb 2022 06:53:51 GMT

As I explained previously, BRPOT only protects the memory (which Bootloader locates) to prevent application code from erasing or writing to protected blocks instead of Ctrl-AP erase.

-Amanda

RE: nRF52840 JTAG disable and don't recover through any JTAG Debugger.

Siddharth Kachhia — Fri, 11 Feb 2022 19:13:26 GMT

If I want to protect Bootloader from JTAG or Debugger Read, then does BPROT protects Bootloader or not ?

RE: nRF52840 JTAG disable and don't recover through any JTAG Debugger.

Amanda Hsieh — Fri, 11 Feb 2022 13:32:51 GMT

Hi,

[quote user="Siddharth Kachhia"]So Suppose If I have protected 1 memory blocks through BPROT(Block Protection) register, though ERASEALL command via CTRL-AP can erase my entire flash, UICR, and RAM ?[/quote]

Yes, see ERASEALL.

[quote user="Siddharth Kachhia"]Does BPROT protect bootloader blocks or only application code ?[/quote]

Yes, see BPROT — Block protection.

-Amanda

RE: nRF52840 JTAG disable and don't recover through any JTAG Debugger.

Siddharth Kachhia — Fri, 11 Feb 2022 13:28:17 GMT

So Suppose If I have protected 1 memory blocks through BPROT(Block Protection) register, though ERASEALL command via CTRL-AP can erase my entire flash, UICR, and RAM ?

Does BPROT protect bootloader blocks or only application code ?

RE: nRF52840 JTAG disable and don't recover through any JTAG Debugger.

Amanda Hsieh — Fri, 11 Feb 2022 13:09:03 GMT

Hi,

BRPOT only protects the memory to prevent application code from erasing or writing to protected blocks instead of Ctrl-AP erase, so it should erase the chip regardless of the BRPOT config.

[quote user="Siddharth Kachhia"]How to erase/write Ctrl-AP port Reg from cmd line ?[/quote]

See the commands in Working with the nRF52 Series' improved APPROTECT

-Amanda

RE: nRF52840 JTAG disable and don't recover through any JTAG Debugger.

Siddharth Kachhia — Fri, 11 Feb 2022 11:38:33 GMT

Ctrl-AP erase can also erase BPROT - Block Protection area of flash or not ?

If I have protected some flash area with BPROT then Ctrl-AP can erase it or not ?

RE: nRF52840 JTAG disable and don't recover through any JTAG Debugger.

Siddharth Kachhia — Fri, 11 Feb 2022 10:29:08 GMT

How to erase/write Ctrl-AP port Reg from cmd line ?

RE: nRF52840 JTAG disable and don't recover through any JTAG Debugger.

Amanda Hsieh — Fri, 11 Feb 2022 09:59:16 GMT

No, not in software, but you could close the JTAG or SWD port in hardware.

-Amanda

RE: nRF52840 JTAG disable and don't recover through any JTAG Debugger.

Siddharth Kachhia — Fri, 11 Feb 2022 09:48:31 GMT

Is it possible to fully disable JTAG and/or SWD?

RE: nRF52840 JTAG disable and don't recover through any JTAG Debugger.

Amanda Hsieh — Fri, 11 Feb 2022 09:34:35 GMT

Hi,

[quote user=""]Now to enable JTAG again, I need to use nrfjprog --recover, which erase flash and UICR to enable flash rd/wr again. After --recover, I can do
flash img and rd/wr register through nrfjprog utility.[/quote]

Yes, this is the new feature of APPROTECT in the nRF52840 Rev3.

[quote user=""]1) What does --recover do with nrfjprog utility ? Is it write/reset any ctrl-AP register to enable JTAG/Debug lines again ?[/quote]

Writing image to disable ap protect, and Erasing user code and UICR flash areas. It erases the device and writes UICR.APPROTECT to HwDisabled (0x5A).

[quote user=""]2) Can I disable --recover in board through any register so that in the field Flash read/write can be disable through any JTAG ?[/quote]

No, this is not support to disable --recover.

[quote user=""]3) If I want to disable JTAG/Debug lines in future, what are the options available for that ?[/quote]

To unlock the device debug port (for debugging etc.), execute the following steps to disable the access port protection:
1. Start with a CTRL-AP ERASEALL operation.
2. Program code compiled with MDK 8.40.2 or later, without ENABLE_APPROTECT defined.
3. Write HwDisabled (0x5A) to UICR.APPROTECT
4. Perform any reset to run the code. The programmed code from step 2 will open access port by writing to APPROTECT.DISABLE during startup.

See https://infocenter.nordicsemi.com/pdf/in_141_v1.1.pdf

Also, have a look at this Working with the nRF52 Series' improved APPROTECT

Regards,
Amanda