Can we auto detect xtal reliably at runtime?

[MabezDev]

I noticed the existence of

esp-hal/esp-hal/src/rtc_cntl/mod.rs

Lines 636 to 657 in ebdd59b

	fn estimate_xtal_frequency() -> u32 {
	// Number of 8M/256 clock cycles to use for XTAL frequency estimation.
	const XTAL_FREQ_EST_CYCLES: u32 = 10;
	let rtc_cntl = unsafe { &*LPWR::PTR };
	let clk_8m_enabled = rtc_cntl.clk_conf().read().enb_ck8m().bit_is_clear();
	let clk_8md256_enabled = rtc_cntl.clk_conf().read().enb_ck8m_div().bit_is_clear();
	if !clk_8md256_enabled {
	RtcClock::enable_8m(true, true);
	}
	let ratio = RtcClock::get_calibration_ratio(RtcCalSel::RtcCal8mD256, XTAL_FREQ_EST_CYCLES);
	let freq_mhz =
	((ratio as u64 * RtcFastClock::RtcFastClock8m.hz() as u64 / 1_000_000u64 / 256u64)
	>> RtcClock::CAL_FRACT) as u32;
	RtcClock::enable_8m(clk_8m_enabled, clk_8md256_enabled);
	freq_mhz
	}
	}

, which we even have an example for.

If we can reliably estimate the xtal freq, we could remove the annoying features we need to supply for the HALs and all the work arounds we do in espflash.

[MabezDev]

Note that if this does work, we'd need to impl for the esp32c6, esp32h2 and esp32p4.

[MabezDev]

In theory, if we can detect the xtal freq, replace the cfgs here:

esp-hal/esp-hal/src/clock/mod.rs

Lines 389 to 392 in ebdd59b

	#[cfg(feature = "xtal-40mhz")]
	let xtal_freq = XtalClock::RtcXtalFreq40M;
	#[cfg(feature = "xtal-26mhz")]
	let xtal_freq = XtalClock::RtcXtalFreq26M;

with autodetection code

[MabezDev]

Closed via #1165