west: Add west rtt command

[topisani]

Implemented in the pyocd and openocd runners while awaiting some feedback.

This command runs separately from a debug session. We should probably also support attaching a rtt client to a running debugserver. However, this might work differently for each runner. pyocd is easy, as it supports a separate RTT command, while openocd and jlink will always need a running server.

See the FIXME's for other points i would like input on.

[MarkoSagadin]

This would be really awesome to have. For our internal processes I created a wrapper around JLinkExeRTTViewer so we could have a single command that does that.

How would enabling a running server be implemented in the case of JLink? As a separate command or an additional flag to the west flash command?

[topisani]

How would enabling a running server be implemented in the case of JLink? As a separate command or an additional flag to the west flash command?

I think the two possible approaches, of which we should maybe do both as separate commands, are:

1. west rtt -r openocd will run the openocd server just like west debugserver does, and attach an rtt client to it.
2. west rtt -r openocd requires you to run west debugserver in another terminal and connects to that.

The first approach is easy, when all you want is to see the log, but the second is more flexible and compatible with the other debug/debugserver/attach commands.

[MarkoSagadin]

I think that second approach makes sense, like you said, it is compatible with other commands.

Two things:

1. Is explicit -r openocd flag needed always? Or just in this PR? I would expect that I can just run west rtt regardless of the runner, if the default one support this, of course.
2. What about if the west rtt command checks if there is a running server (by checking known ports maybe?) and creates a new one (like suggested in your first case) if none is found? This would then support the easy use case that you describe. So something like:

   west build -b <some_board> && west flash && west rtt
   

[topisani]

1. Is explicit `-r openocd` flag needed always? Or just in this PR? I would expect that I can just run `west rtt` regardless of the runner, if the default one support this, of course.

No, i just always use it, because the default runner is usually not what i want

2. What about if the `west rtt` command checks if there is a running server (by checking known ports maybe?) and creates a new one (like suggested in your first case) if none is found? This would then support the easy use case that you describe.  So something like:

I consideren this option, but i think its nicer to have it either as a separate command, or as an argument. Connecting to arbitrary ports when not asked to is probably a no go. Besides, consistent behavior seems preferable

[pdgendt]

Looks very neat BTW

[topisani]

LMK if i should have pushed this latest commit to a different PR, now that this had been partially approved. I just thought id better get this jlink support in along with the rest.

jlink support is implemented in much the same way as openocd, except it can better automatically locate the rtt block, so it relies on that.

[fabiobaltieri]

Cool, second commit message is stale I guess, feel free to update it.

[topisani]

Cool, second commit message is stale I guess, feel free to update it.

Any objections to me just squashing all three commits?

[fabiobaltieri]

Any objections to me just squashing all three commits?

Yes, don't. :-) Just reword the second commit message, the rest is fine as it is.

[topisani]

alright, reworded and reordered, apparently i had swapped the first two commits somewhere along the way

[pdgendt]

A follow-up PR to add this to the documentation would be nice.