drivers/sx126x: improve hardware detection

[maribu]

Contribution description

• split out the detection logic into a static helper function
• replace a forgotten debug printf() with DEBUG()
• add a LOG_ERROR() to when no device is detect to ease diagnosis of a failing SPI bus / incorrect wiring / broken chip
• use a bullet-proof test:
  • First set the modulation type to LoRa
  • Then get the modulation type and expect it to be LoRa

Even if the reset of the devices fails (e.g. because the reset signal
is not connected) and the modulation would be different from LoRa, this
now should reliably detect the chip.

Testing procedure

This should 100% detect when hardware is present, and 99.99% detect when hardware is not present.

Issues/PRs references

None

[riot-ci]

Murdock results

✔️ PASSED

fba614b drivers/sx126x: improve hardware detection

Success	Failures	Total	Runtime
10932	0	10932	14m:04s

Artifacts

• Documentation preview

[maribu]

I have one very cursed setup where setting the packet type (modulation type) to LoRa then reading it back looks like this:

On the second attempt it looks like this:

I updated this PR to do three attempts at the detection, as I believe this might make the cursed hardware work. Testing will have to wait until Monday. I'll keep this as a draft until it is tested.

Some context: The expected transfer is:

1. Writing packet type Lora
   1. Sending 0x8a (CMD "set packet type), 0x01 (data "packet type LoRa")
2. Reading packet type
   1. Sending 0x11 (CMD "get packet type), 0x00 (data "don't care")
   2. Reading 0x01 ("packet type Lora")

At the first attempt the devices keeps MISO just high, as if it is completely unresponsive. The packet type is then read as 0xff as consequence. On the the second attempt it works as expected.

[maribu]

I updated the PR to no longer try three times. After the power sequencing code of the cursed board was fixed, the board was less cursed and the chips reliably come up on the first try.

I don't have a reason to believe that there is a benefit in retrying the detection, hence I removed this.