Experimental ESP32 support using espressif arduino-esp32 core

[ziotibia81]

Tested using the ESP-WROOM-32 module.
This module uses a 40 MHz crystal oscillator (+/- 10 ppm).
The hardware GPTimer is prescaled to tick at 1 MHz, and the 1 kHz generator is triggered by an interrupt every 1000 ticks.

[udoklein]

Hi Zio Tibia, thanks for providing these changes. Are they still experimental or do you consider them production ready? Right now I have no means to verify if this works for ESP32 and or ESP8266.

[ziotibia81]

I was able to run SperFilter, adjusting the GPIO declarations, but these are not included in this PR. I reached a synchronized state in approximately 550 seconds in a low-noise environment. I repeated this process over several days, and the result remained consistent.

Toggling an output pin each time the ISR occurs allows me to measure a precise frequency of 500.0 Hz with a 50% duty cycle, using a hobby-level oscilloscope.

[udoklein]

Can you please issue a new pull request such that I can merge onto the new master? Sorry for being slow and lazy - right now I have very little time and lack the hardware setup for testing.

[Anderl94]

Hi, just checking in. Any updates on this pull request?

[ziotibia81]

Hello @Anderl94 ,
I haven't had time yet to modify the pull request as per @udoklein 's instructions.
If you want to do some testing, you can use the branch ziotibia81/dcf77@esp32-patch-1 in my repository .