adc: multichannel continuous conversion

[yjh0502]

related: #212

Add support for multichannel continuous conversion.

[TheZoq2]

Sorry for the delay

The changes look good over all, I left some small comments in the review thingy.

Also, would you mind adding a changelog entry to CHANGELOG.md?

[TheZoq2]

Lingoring TODO

[yjh0502]

I added a validation on ADC DMA buffer length

• When a buffer is larger than ADC conversion length, DMA will fill the buffer partially.
• When a buffer is smaller than ADC conversion length, it will panic. I'm not sure if it's a best way to handle the case.

[TheZoq2]

Hmm, I'm not sure what the best behaviour would be here. I'd almost argue that a panic is best in both cases (unless we can return a result).

[TheZoq2]

Why is the sequence 4 samples?

[yjh0502]

No specific reason, I started from rustdoc example :)

stm32f1xx-hal/src/adc.rs

Lines 531 to 544 in 1357e5a

	/// Set channel sequence and sample times for custom pins
	///
	/// Example:
	/// ```rust, ignore
	/// pub struct AdcPins(PA0<Analog>, PA2<Analog>);
	/// impl SetChannels<AdcPins> for Adc<ADC1> {
	/// fn set_samples(&mut self) {
	/// self.set_channel_sample_time(0, adc::SampleTime::T_28);
	/// self.set_channel_sample_time(2, adc::SampleTime::T_28);
	/// }
	/// fn set_sequence(&mut self) {
	/// self.set_regular_sequence(&[0, 2, 0, 2]);
	/// }
	/// }

[yjh0502]

I pushed new PR, including

• Rebase
• Update CHANGELOG.md
• Try to validate buffer length on ADC DMA conversion.