cpu/nRF52: Always recover Device before Flashing

[crasbe]

Contribution description

With nRF52 silicon revision Fxx and newer, the behavior of the APPROTECT flash protection was changed. Previously it had to be activated manually and as long as it was not activated, the flash could be read from and written to without issues.
After the revision, the device is in a protected state after the first power cycle, making it impossible to read/write/modify the flash memory with an external debugger.

Furthermore, the device has to be unlocked (or in Nordic terms "recovered") explicitly. Unlike the term "recover" might suggest, the flash is erased during that "recovery".
The Segger J-Link does that recovery process implicitly, while OpenOCD has a dedicated nrf52_recover command for it which has to be called after the init command and before any other command.

This necessitated the introduction of another OpenOCD variable, which is between the init and the following target command in the flash procedure, called OPENOCD_POST_INIT_CMDS.

This variable is defined in the shared boards/common/nrf52/Makefile.include and is therefore set for all nRF52 devices. When not using OpenOCD, it does not have any effect and there should not be any adverse effects on other programmers.

A side effect is that earlier silicon revisions might get their flash memory erased by the nrf52_recover command even though it is not necessary for them, but adding a distinction for the old chips is beyond the scope of the RIOT flashing scripts I think.

Testing procedure

Programming any nRF52 board using an external programmer (J-Link or ST-LINK) in conjunction with OpenOCD with the newer silicon revisions should throw an OpenOCD error about the missing recovery command with the current master.

chris@ThinkPias:~/flashdev-riot/RIOT$ PROGRAMMER=openocd BOARD=nrf52840dk make -C examples/hello-world flash -j12
make: Verzeichnis „/home/chris/flashdev-riot/RIOT/examples/hello-world“ wird betreten
Building application "hello-world" for "nrf52840dk" with CPU "nrf52".

"make" -C /home/chris/flashdev-riot/RIOT/pkg/cmsis/ 
...
"make" -C /home/chris/flashdev-riot/RIOT/cpu/cortexm_common/periph
   text    data     bss     dec     hex filename
  11456     108    2328   13892    3644 /home/chris/flashdev-riot/RIOT/examples/hello-world/bin/nrf52840dk/hello-world.elf
/home/chris/flashdev-riot/RIOT/dist/tools/openocd/openocd.sh flash /home/chris/flashdev-riot/RIOT/examples/hello-world/bin/nrf52840dk/hello-world.elf
### Flashing Target ###
Open On-Chip Debugger 0.11.0
Licensed under GNU GPL v2
For bug reports, read
        http://openocd.org/doc/doxygen/bugs.html
swd
Info : J-Link EDU Mini V1 compiled Apr 15 2024 17:39:18
Info : Hardware version: 1.00
Info : VTarget = 2.992 V
Info : clock speed 1000 kHz
Info : SWD DPIDR 0x2ba01477
Error: Could not find MEM-AP to control the core
****** WARNING ******
nRF52 device has AP lock engaged (see UICR APPROTECT register).
Debug access is denied.
Use 'nrf52_recover' to erase and unlock the device.

Warn : target nrf52.cpu examination failed
Info : starting gdb server for nrf52.cpu on 0
Info : Listening on port 39965 for gdb connections
    TargetName         Type       Endian TapName            State       
--  ------------------ ---------- ------ ------------------ ------------
 0* nrf52.cpu          cortex_m   little nrf52.cpu          unknown

Error: Could not find MEM-AP to control the core
****** WARNING ******
nRF52 device has AP lock engaged (see UICR APPROTECT register).
Debug access is denied.
Use 'nrf52_recover' to erase and unlock the device.

Error: Target not examined, reset NOT asserted!

With this PR, it should just work. I tested it with a J-Link EDU (an unrelated issue prevents using the builtin J-Link with the latest firmware) and a Nordic Semiconductor nRF52840 DK (PCA10056 Revision 3.0.1 from 2023.6).

chris@ThinkPias:~/flashdev-riot/RIOT$ PROGRAMMER=openocd BOARD=nrf52840dk make -C examples/hello-world flash -j12
make: Verzeichnis „/home/chris/flashdev-riot/RIOT/examples/hello-world“ wird betreten
Building application "hello-world" for "nrf52840dk" with CPU "nrf52".
...
   text    data     bss     dec     hex filename
  11472     108    2328   13908    3654 /home/chris/flashdev-riot/RIOT/examples/hello-world/bin/nrf52840dk/hello-world.elf
/home/chris/flashdev-riot/RIOT/dist/tools/openocd/openocd.sh flash /home/chris/flashdev-riot/RIOT/examples/hello-world/bin/nrf52840dk/hello-world.elf
### Flashing Target ###
Open On-Chip Debugger 0.11.0
Licensed under GNU GPL v2
For bug reports, read
        http://openocd.org/doc/doxygen/bugs.html
swd
Info : J-Link EDU Mini V1 compiled Apr 15 2024 17:39:18
Info : Hardware version: 1.00
Info : VTarget = 2.990 V
Info : clock speed 1000 kHz
Info : SWD DPIDR 0x2ba01477
Error: Could not find MEM-AP to control the core
****** WARNING ******
nRF52 device has AP lock engaged (see UICR APPROTECT register).
Debug access is denied.
Use 'nrf52_recover' to erase and unlock the device.

Warn : target nrf52.cpu examination failed
Info : starting gdb server for nrf52.cpu on 0
Info : Listening on port 35695 for gdb connections
Waiting for chip erase...
nrf52.cpu device has been successfully erased and unlocked.
Info : nrf52.cpu: hardware has 6 breakpoints, 4 watchpoints
Error: nrf52.cpu -- clearing lockup after double fault
Polling target nrf52.cpu failed, trying to reexamine
Info : nrf52.cpu: hardware has 6 breakpoints, 4 watchpoints
    TargetName         Type       Endian TapName            State       
--  ------------------ ---------- ------ ------------------ ------------
 0* nrf52.cpu          cortex_m   little nrf52.cpu          halted

target halted due to debug-request, current mode: Thread 
xPSR: 0x01000000 pc: 0xfffffffe msp: 0xfffffffc
Info : nRF52840-xxAA(build code: F0) 1024kB Flash, 256kB RAM
Warn : Adding extra erase range, 0x00002d3c .. 0x00002fff
auto erase enabled
wrote 11580 bytes from file /home/chris/flashdev-riot/RIOT/examples/hello-world/bin/nrf52840dk/hello-world.elf in 0.511253s (22.119 KiB/s)

verified 11580 bytes in 0.079247s (142.701 KiB/s)

shutdown command invoked
Done flashing
make: Verzeichnis „/home/chris/flashdev-riot/RIOT/examples/hello-world“ wird verlassen

Issues/PRs references

This solves #20968 (at least the issues we can fix from RIOTs side).

[mguetschow]

Thanks, looks good! Just a minor comment below.

[riot-ci]

Murdock results

✔️ PASSED

168829f boards/nrf52: always recover device before flashing with OpenOCD

Success	Failures	Total	Runtime
10215	0	10215	17m:27s

Artifacts

• Documentation preview

[mguetschow]

Confirmed to work locally with a nRF52840dk, revision PCA10056. Thanks a bunch!

[crasbe]

I'm not sure how this PR broke the 'tests/sys/xtimer_usleep_short' test on native64? 🤔😅

[mguetschow]

Probably an unrelated spurious failure, let's retry :)

[crasbe]

Probably an unrelated spurious failure, let's retry :)

Awesome, thank you :)
Now it merged fine.