System locked when RTC data is broken

[padcom]

Is there an existing issue for this problem?

• I have searched the existing issues

What part of EdgeTX is the focus of this bug?

Transmitter firmware

Current Behavior

When the RTC data is broken, the transmitter will not turn on. The bootloader starts ok. No indication of the situation of broken RTC data.

Expected Behavior

The transmitter turns on.

Steps To Reproduce

1. Get a transmitter with broken RTC data
2. Turn the transmitter on
3. Observe it is locked

Version

2.8.0

Transmitter

Radiomaster TX16S / TX16SMK2

Anything else?

The problem is with __mktime_internal and its processing:

edgetx/radio/src/rtc.cpp

Lines 396 to 407 in 1bffd26

	/* Repeatedly use the error to improve the guess. */
	for (t = t1 = t2 = t0;
	(gt = guess_time_tm(year, yday, hour, min, sec, &t, ranged_convert(convert, &t, &tm)), t != gt);
	t1 = t2, t2 = t, t = gt) {
	if (t == t1 && t != t2)
	goto offset_found;
	else if (--remaining_probes == 0)
	return -1;
	}
	offset_found:
	*offset = guessed_offset + t - t0;

With broken data this loop never finishes.

[raphaelcoeffic]

We should probably add some unit tests for gmktime to test this properly with invalid values.

[padcom]

The idea behind this PR is to know when the problem occurs to help diagnose it - not to fix the underlying problem. It occurs rarely and at present finding out what happened is next to impossible for users without programming skills.

I presume there will be another PR, done by someone who has much deeper knowledge about the platform, that will try to address the root cause of the problem.