Light sleep and timers

[blubb]

I found out that the automatic (not forced) light sleep (i.e. wifi_set_sleep_type) cannot be used with the os timers (os_timer_arm etc.). The timers become very unreliable. That is because CPU and clock is halted, right?

Now I wonder how the forced sleep functions work. I mean it is possible to set a timeout and still use light sleep, e.g.
wifi_fpm_do_sleep(50*1000);

What is their clock source and why can't this be implemented in the automatic light sleep functionality?

[pratik]

The RTC peripheral memory and clock do work even when there is no active CPU. That is how events like deep sleep wake-up, etc are timed. The timer runs off the standard peripheral clock (which consumes lots of power), so regular timers are turned off.

What exactly is your system requirement? I can help find the sleep mode that will suit your application most.

[blubb]

I have a web server running on the ESP. Also there is a timer (using os_timer_arm) which occurs every minute. There is not much to be done during that minute (usually).
So using MODEM sleep works. The web server is accessible all the time and also the timer callback is precisely called.

But in my opinion LIGHT sleep would be better. Wifi access is still ok (light sleep is interrupted by wifi), but the timer won't work anymore (at least not reliably). If there is no wifi access, the timer "oversleeps". So what I would need is an option to tell the automatic LIGHT sleep when to wake up. Like an RTC alarm of some kind.

[pratik]

Light sleep turns the CPU off, so timed light sleep is a bit of an issue. Also, to use light sleep, wifi radio must be in NULL mode (radio off!).
So modem sleep is what you should use.
When ESP is the AP, power saving is not practical. An AP must stay up all the time. You can lower the transmit strength and PHY mode to save power if you wish to.
If you have ESP in station mode and server is enabled, then enable auto light-sleep or modem sleep, which will save power.

[blubb]

If you have ESP in station mode and server is enabled, then enable auto light-sleep

This is exactly my case. But the timers get unreliable since the wake ups from light sleep depend on the signals from my wifi router. Sometimes nothing is received and the timers oversleep.
This is why I am using modem sleep.

It is unfortunate there is no other way to save more power.

An option to wake up from automatic light sleep every x seconds would be great...

[pratik]

The nature of light sleep prevents such functionality, because it makes the core sleep and wireless activity must stop. You will need an external trigger to wake it up then.

[blubb]

So it could be done if there was a way to configure the RTC wakeup timer using a simple api function.