AP_RTC: allow time to shift forward when disarmed

[peterbarker]

No description provided.

[peterbarker]

... the sanity check for no-backwards-times is further down in the function.

[tridge]

we will add drift logic, @davidbuzz or @Hwurzburg will test with F765 wing or Mambaf405v2
we need drift for fwd and backward drift

[davidbuzz]

for that clock drift issue... i connected a ublox to my f765-wing, formatted the sd card, then set:
LOG_DISARMED=1
LOG_REPLAY=1
.. then stick it outside for an hr ?
[ I have just done that]

[davidbuzz]

1hr log for analysis here: https://drive.google.com/file/d/1l43Fx9f2w9vN-kFDkhAQUygRwL_2XwhE/view?usp=drive_link

[davidbuzz]

side note, this log also has an internal error in it, possibly storage related.?

Storage: failed at 0:4154 for 8 - re-init 1
AP: Internal Errors 0x8000
... and a bit later
PreArm: Internal errors 0x8000 l:443 main_loop_stk

got this log on a normal f765-wing on the ground, logging while disarmed, with the only hardware connected is a gps , power ,and a usb cable.

AP: ArduPlane V4.5.0-dev (7234ec2)
AP: ChibiOS: a287e67d
AP: MatekF765-Wing 0031002A 34385105 34313531 (edited)

[ ie a recent 'latest' build from the autotest build server from the last week or 2?]

[davidbuzz]

re-ran test, and at about 1/2hr, the internal error came again..
Critical failure 0x8000 sysid=1 compid=1
AP: PreArm: Internal errors 0x8000 l:443 main_loop_stk
[this time i did not get a 'Storage: failed at xxx' ] that i saw.
the file named 222.bin at https://drive.google.com/file/d/17zTj43ID5CasyDOQSdevSlBo51P1eR75/view?usp=drive_link

[davidbuzz]

testing with a different SD card done... does not Internal Error with different SD card after an hr.
https://drive.google.com/file/d/10xtP3R3KByDtDLcHPNViJ_A2IjJKrIL0/view?usp=drive_link

[tridge]

add log of 64 bit UTC time in STAT

[peterbarker]

This is an autopilot getting a GPS fix:

[peterbarker]

add log of 64 bit UTC time in STAT

Had to go with PM instead - STAT is actually a Plane-specific message to do with is-flying huristics for the most part.... I keep forgetting that.

[peterbarker]

This broke the documentation. Fixed here: #28695