Timer corruption issue

Description

Setting the "wall time" on the same function call as a timer set to MGOS_TIMER_RUN_NOW corrupts the timer and breaks all timer invocations.

We have a requiement to as much as possible, not lose the system clock, for that we set a reboot handler that writes the current wall time on reboot using an event handler.

On boot, we set a timer with the MGOS_TIMER_REPEAT and MGOS_TIMER_RUN_NOW flags, then we set the wall time with mgos_settimeofday, this sets the timer's next_invocation to a negative number, breaking the timer and any other timer, including cron jobs!

App Config Schema

• save_time: Enable saving the wall time on reboot
• long_timer: Enabling setting the long timer that runs instantly BEFORE setting any saved wall time.
• saved_time: Saved wall time

Reproduction steps

• Build and flash the app, run mos console.
• On first run a "Long Timer" log should show up, which is the timer set to run instantly. It should also show up after 60 seconds.
• Every 5 seconds a second timer should trigger logging the text "Timer" on console as well'
• With the console running paste the RPC command for a reboot. {"method": "Sys.Reboot", "id": 123}, it should reboot the board, if not just call mos call Sys.Reboot && mos console to send the command and continue monitoring the console.
• After the reboot the "Long Timer" message will not show up on boot, nor the "Timer" message that should show up every 5 seconds. No other timer will work again on this board. Not even a Sys.Reboot RPC command will work because the board sets a 100 ms timer before actually doing the reboot.
• To fix, a hardware reboot is needed.

Visualization

Apply the patch file mgos_timers.c.patch to the mgos_timers.c file. With a local build the command should be patch deps/modules/mongoose-os/src/mgos_timers.c mgos_timers.c.patch

This patch adds a few logs when setting, clearing and when the mgos_time_change_cb is triggered by changing the wall time.

Here's a sample of the failed state:

[Jan  8 17:01:36.089] mgos_timers.c:130       Setting timer with id 1073508848
[Jan  8 17:01:36.095] mgos_timers.c:193       Updated timer 1073508848 to invocation -1.812651
[Jan  8 17:01:36.101] main.c:33               Wall time set to 5 from config
[Jan  8 17:01:36.331] mgos_sys_config.c:174   Saved to conf9.json
[Jan  8 17:01:36.334] mgos_timers.c:130       Setting timer with id 1073511848
[Jan  8 17:01:36.341] mgos_init.c:36          Init done, RAM: 287336 total, 227684 free, 227020 min free
[Jan  8 17:01:37.349] mgos_mongoose.c:66      New heap free LWM: 225896