Make ulp timer clock for sync all time regs like gnns and gps, and gsm messages

[jprpower104]

(Only RTC or ULP Timer) I need make a continuosly square signal with a width of 0.5 ms in on and 0.5 ms in off, for make a clock system, this clock can operate in normal mode, and in deep sleep, and in ligth sleep. This timer can drive a led too, turn on or turn off a physical led each the logic level of timer changes. I need do this with interruptions because with a polling strategy we can loss a bit of time.

Can you help to me for program a timer signal in ulp with a big grade of exact and presision.