periph/timer: API inconstency

[OlegHahm]

Reviewing #4089 I realized that periph/timer API seems to be inconsistent. timer_init() returns 0 on success, while all other functions return 1 on success. I think all periph functions which just return a boolean value should return the same one. Ideally this would be rather a macro like PERIPH_SUCCESS than a literal.

[dkm]

same kind of inconsistency exists in nrf24l01p driver : some functions return 0 (preload, unregister, ...) on success, some return 1 (set_channel, ...).

[PeterKietzmann]

@dkm you're right. As stated in #4389 I think the whole driver could need some rework. But it's not part of this issue :-)

[haukepetersen]

all driver interfaces except spi and i2c have been reworked, and including these two they all have the same return values.

@OlegHahm: is this enough to close this PR, or do you insist on some macro on top of this?

[A-Paul]

It may be a surprise, ;-) but I still recommend using macros. Not sure if there is need to list all the advantages...
I might help finding names and applying them.
Preferably after this release.

[haukepetersen]

I don't care (though I am not a fan of it). So lets keep this issue open.

[OlegHahm]

1. I don't see the initial issue solved. timer_init() still returns 0 on success, while the other functions return 1 on success.
2. I agree with @A-Paul here, that macros would be preferable (and would help to avoid such a confusion).

[kYc0o]

Still inconsistent. Let's move it for the next release.

[miri64]

This somehow flew under my radar. Postponed.

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. If you want me to ignore this issue, please mark it with the "State: don't stale" label. Thank you for your contributions.