Contribution description

Most details of this PR are detailed in #20775. tl;dr: In the makefiles/tools/jlink.inc.mk file, a % wildcard is used for the flash targets that includes all variants of flash... but not flash itself. Therefore important environment variables are not exported as they should be and others like JLINK_PRE_FLASH and JLINK_POST_FLASH do not work.

Additionally, the JLINK and JLINK_POST_FLASH variables were not exported at all. The former did not have an effect because the JLINK variable has a backup in dist/tools/jlink/jlink.sh. However it is defined in multiple places, for example in boards/common/nrf52/Makefile.include, so it would be good to actually use the defined value and not the fallback value.
The latter is not currently used by any boards, so it did not have an effect. However I want to use it, so this PR creates the basis for that.

The debug% wildcard seems to call another target as well, so it is not affected? But I could add JLINK_DEBUG_TARGETS in a similar way to JLINK_FLASH_TARGETS and also add debug debug%.

Testing procedure

Of course, everything should still work as it should. Only very few boards use the JLINK_PRE_FLASH variable, but one that does is stk3200.
To test that this PR has the effect it should, you can compile for example examples/default with BOARD=stk3200 make flash (even if you don't have one, we don't need to actually flash it) and check the content of examples/default/bin/stk3200/burn.seg.

Without the PR, this is the content of burn.seg. The JLINK_PRE_FLASH = r from boards/stk3200/Makefile.include was ignored.

chris@ThinkPias:~/flashdev-riot/RIOT/examples/default$ cat bin/stk3200/burn.seg 
loadfile /home/chris/flashdev-riot/RIOT/examples/default/bin/stk3200/default.elf
r
g
exit

With the PR applied the output should look like this:

chris@ThinkPias:~/flashdev-riot/RIOT/examples/default$ cat bin/stk3200/burn.seg 
r
loadfile /home/chris/flashdev-riot/RIOT/examples/default/bin/stk3200/default.elf
r
g
exit

To test if the JLINK variable is properly exported, you can temporarily modify the boards/common/nrf52/Makefile.include and insert a random command for JLINK, in this case uname. It has to run successfully, otherwise the script will select openocd.

# set list of supported programmers
PROGRAMMERS_SUPPORTED += openocd bmp
# keep name of `JLINK` in sync with script jlink.sh in $(RIOTTOOLS)/jlink
- JLINK ?= JLinkExe
+ JLINK ?= uname
ifneq (,$(shell command -v $(JLINK)))
  PROGRAMMER ?= jlink
else
  PROGRAMMER ?= openocd
endif

Before applying the PR, the change of command does not have any effect and it should call JLinkExe anyway:

chris@ThinkPias:~/flashdev-riot/RIOT/examples/default$ BOARD=nrf52840dk make flash
Building application "default" for "nrf52840dk" with CPU "nrf52".

"make" -C /home/chris/flashdev-riot/RIOT/pkg/cmsis/ 
...
"make" -C /home/chris/flashdev-riot/RIOT/sys/net/gnrc/netif/pktq
   text	   data	    bss	    dec	    hex	filename
  45900	    172	   6452	  52524	   cd2c	/home/chris/flashdev-riot/RIOT/examples/default/bin/nrf52840dk/default.elf
/home/chris/flashdev-riot/RIOT/dist/tools/jlink/jlink.sh flash /home/chris/flashdev-riot/RIOT/examples/default/bin/nrf52840dk/default.elf
### Flashing Target ###
### Flashing elf file ###
SEGGER J-Link Commander V7.96e (Compiled Apr 17 2024 16:28:22)
DLL version V7.96e, compiled Apr 17 2024 16:27:56
...

After applying the PR, the error message Error: J-Link appears not to be installed on your PATH should be reported, because the dist/tools/jlink/jlink.sh script interprets the output of JLinkExe and obviously uname does not produce the correct output.

chris@ThinkPias:~/flashdev-riot/RIOT/examples/default$ BOARD=nrf52840dk make flash
Building application "default" for "nrf52840dk" with CPU "nrf52".

"make" -C /home/chris/flashdev-riot/RIOT/pkg/cmsis/ 
...
"make" -C /home/chris/flashdev-riot/RIOT/sys/ztimer
   text	   data	    bss	    dec	    hex	filename
  45932	    172	   6452	  52556	   cd4c	/home/chris/flashdev-riot/RIOT/examples/default/bin/nrf52840dk/default.elf
/home/chris/flashdev-riot/RIOT/dist/tools/jlink/jlink.sh flash /home/chris/flashdev-riot/RIOT/examples/default/bin/nrf52840dk/default.elf
### Flashing Target ###
### Flashing elf file ###
Error: J-Link appears not to be installed on your PATH
make: *** [/home/chris/flashdev-riot/RIOT/examples/default/../../Makefile.include:844: flash] Fehler 1

Issues/PRs references

See also #20775.