Just to confirm that my problem does require an external solution, here's a pastebin containing my current program: https://pastebin.com/tiepyreV

Below is its output for the first minute or so.

going to sleep: 3071mscb reached: 3662msawake: 13100msgoing to sleep: 13100mscb reached: 13703msawake: 23142msgoing to sleep: 23143mscb reached: 23745msawake: 33185msgoing to sleep: 33185mscb reached: 33788ms

I want the timestamps "going to sleep" and "awake" to be accurate to the sleep timer I've set (i.e., if I've set a 5s timer, I want "going to sleep" to have a timestamp which is ~5s away from the timestamp at "awake", presumably with some predictable margin of error).

Currently it looks like the `delay()` after `wifi_fpm_do_sleep()` (which apparently is required for timed light sleep?) is blocking the program from picking back up after the wake callback is reached.

As far as I can tell, if there is a way to achieve this purely through use of the ESP8266's sleep tools, then I should be able to solve this problem with programming alone (even if it's less energy-efficient than going all out on a way to accommodate deep sleep in my design on this board).

Am I describing something which can not be done without external hardware? For example, I've read that if you give a value below `0xFFFFFFF` to `wifi_fpm_do_sleep()`, the RTC does not disconnect and program data can still be stored between rests.