drivers/periph/spi: add doc about multiple SPI buses

[crasbe]

Contribution description

As discussed in the Weekly, the documentation of the SPI peripheral could be extended.

Also, in the last RIOT seminar at TUHH the question came up what SPI_DEV even is, this is not really addressed here yet.

Perhaps replicate this for I2C and UART?

Testing procedure

Read the doc.

Issues/PRs references

None.

Declaration of AI-Tools / LLMs usage:

AI-Tools / LLMs that were used are:

• none

[riot-ci]

Murdock results

✔️ PASSED

be59d09 doc/guides/creating_app: add info about custom periph_conf.h

Success	Failures	Total	Runtime
1	0	1	01m:12s

Artifacts

• Documentation preview

[mguetschow]

Thanks! Should we add a hint as to how people are expected to change those (i.e., custom board or custom periph_conf.h)?

Perhaps replicate this for I2C and UART?

Yes, please!

[mguetschow]

Suggested change

	* such as the Nordic Semiconductor nRF52 family even allow arbitrary pin
	* such as the Nordic Semiconductor nRF52 family, even allow arbitrary pin

maybe also add a reference/link to it?

[crasbe]

Not sure where to link to in this case, but also in the past I've been told in reviews to avoid overly specific pieces of information in documentation. So I'd probably keep the level of details at this level 🤔

[crasbe]

Thanks! Should we add a hint as to how people are expected to change those (i.e., custom board or custom periph_conf.h)?

Perhaps the board porting guide world be a good place for additional information, not sure where to put information for a user.

I don't really want to edit every periph_conf.h file to add a hint.

Perhaps replicate this for I2C and UART?

Yes, please!

In follow up PRs though :)

[crasbe]

Thanks! Should we add a hint as to how people are expected to change those (i.e., custom board or custom periph_conf.h)?

Perhaps the board porting guide world be a good place for additional information, not sure where to put information for a user.

So I just tested it and you can put a custom periph_conf.h in your application's base directory that is chosen instead of the board's periph_conf.h. AFAIK this is not documented anywhere yet, but the https://doc.riot-os.org/c_tutorials/create_project/ or https://doc.riot-os.org/advanced_tutorials/creating_application/ guide would probably be the best place for it. Then I can add a half sentence to the end that already points to the periph_conf.h and refer to the appropriate chapter in the guide.

[AnnsAnns]

Wanna wait for @mguetschow approval?

[crasbe]

Applied the same fix as in #22192.

[crasbe]

Wanna wait for @mguetschow approval?

I was hoping for some feedback from @carl-tud, who raised the issue and perhaps from @miri64 to check if I documented the periph_conf.h feature correctly. She pointed to that feature existing. 😅

The merge queue won't drain today anyway, so we can also just wait one more day for Mikolai :)