ADC slides: migrate to adc_read_dt() / adc_read_async_dt() with return value coverage

[Copilot]

The ADC slides were using the legacy adc_read(dev, &seq) / adc_read_async(dev, &seq, &sig) APIs that require manually dereferencing .dev from the DT spec struct. The current recommended pattern passes the adc_dt_spec directly.

Changes in slides/zephyr-adc.qmd

• Sync read — replace adc_read(adc_vadc.dev, &sequence) with adc_read_dt(&adc_vadc, &sequence); add inline return-value documentation:

  // Return values: 0 on success, -EINVAL (bad param), -ENOMEM (buffer too small),
  //                -ENOTSUP (mode not supported), -EBUSY (previous sampling still in progress)
  ret = adc_read_dt(&adc_vadc, &sequence);

• Async read — replace adc_read_async(adc_dev, &sequence, &adc_signal) with adc_read_async_dt(&adc_vadc, &sequence, &adc_signal); add error-checking on the return value

• Return value coverage — add a bullet list in the "Asynchronous ADC" section explicitly documenting all return codes (0, -EINVAL, -ENOMEM, -ENOTSUP, -EBUSY) and clarifying that the return is immediate — it signals whether the sequence was started, not completed

• Prose — update all remaining adc_read()/adc_read_async() references (including the callout-tip) to use the _dt variants

[Copilot]

Pull request overview

Updates the Zephyr ADC slide deck to use the recommended adc_*_dt() APIs that accept struct adc_dt_spec * directly, and expands the documentation around asynchronous return values to reduce confusion about “started vs completed”.

Changes:

• Migrate synchronous reads to adc_read_dt(&adc_vadc, &sequence) and document expected return codes inline.
• Migrate asynchronous reads to adc_read_async_dt(&adc_vadc, &sequence, &adc_signal) and add basic return-value checking.
• Expand “Asynchronous ADC” section to explicitly document immediate return semantics and error codes.

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[Copilot]

The note "no .dev member needed" is a bit ambiguous in this snippet because .dev is still used for logging just above; consider rephrasing to clarify that .dev is not needed for the adc_read_dt() call, but the dt spec still contains .dev for other uses (e.g., name/ready checks).

Suggested change

	// adc_read_dt() takes the adc_dt_spec struct directly (no .dev member needed)
	// adc_read_dt() takes the adc_dt_spec struct directly; for this call, do not pass `.dev`.
	// The dt spec still contains `.dev` for other uses, such as logging the device name above.

[Copilot]

If adc_read_async_dt() fails (ret < 0), the slide's flow still proceeds to a k_poll(..., K_FOREVER) wait below, which would block forever because no signal will be raised. Consider returning/branching on error (or using a finite timeout) so the example can't deadlock when startup fails.