ESP32 SNTP sys.tz_spec weird result

[alnunez]

Hi
I'm working with an ESP32 with mongoose OS V2.19.1.
Added SNTP library and setup and tried tho configure time zone for AMERICA/BOGOTA adding the following line to mos.yml

• ["sys.tz_spec", "<-05>5"]

Bogota Time is UTC-5, however, after rebooting and SNTP sync the time showed was Greenwich plus 5 hours!!. Just for curiosity, changed the line this time to:

• ["sys.tz_spec", "<+05>5"]

Rebooted, and SNTP synced. Now the time is correct!. Does somebody experienced the same thing?

[scaprile]

May I suggest you go to the forum and search there ? I've answered this at the forum and even have working examples in Spanish

[DrBomb]

Some questions:

• How did you read the time shown? Because the SNTP library shows you the unix timestamp on update regardless of your tz_spec value
• tz_spec only affects a very specific subset of functions. localtime_r is one of them, while other functions like the widely used mg_time() will only return unix time as it should. What are you using?

Time inside C functions, and specially on mongoose can be complicated for begginers. I would suggest, @alnunez, that you make a sample app if you think that indeed, this is a bug on the code.

Good luck!

[alnunez]

Here is the exact piece of code. A function that builds a message, including datetime. Timer.fmt() seems affected by tz_spec, because i tried different values, and all of them changed the time zone when printing timestamp.

function buildMsgUl(){

message_ul.sensor_id=DEVICE_ID;	
let extTemperatureCstr = roundNdigitsTostr(getTempC(),2);
message_ul.temperature_ext=extTemperatureCstr;
let intTemperatureCstr = roundNdigitsTostr((5/9)*(ESP32.temp()-32),2);
message_ul.temperature_int=intTemperatureCstr;	
let batVstr = getBatV();
message_ul.battery=roundNdigitsTostr(batVstr,2);
let timeunix = Timer.now();
let timestamp = Timer.fmt('%Y-%m-%d %H:%M:%S',timeunix);	
message_ul.timestamp = timestamp;

}

[DrBomb]

mJS is outside my expertise, I don't use it.

That said, here's your reason https://unix.stackexchange.com/questions/104088/why-does-tz-utc-8-produce-dates-that-are-utc8

Basically the POSIX tz formats are 3 letters plus the offset. But the offset has to be on the opposite sign. Hence why ["sys.tz_spec", "<+05>5"] worked for you. Just use that one.

[alnunez]

Well after some more experimentation i found some discrepancies in tz for America/Bogota as follows:

from: https://github.com/mamuesp/timezones "America/Bogota":"<-05>5"
This value doesn't work, gave time UTC+5

from: https://github.com/openwisp/netjsonconfig/blob/master/netjsonconfig/backends/openwrt/timezones.py "America/Bogota", "COT5"
This value Works OK as expected (gave time UTC-5 )

[alnunez]

mJS is outside my expertise, I don't use it.

That said, here's your reason https://unix.stackexchange.com/questions/104088/why-does-tz-utc-8-produce-dates-that-are-utc8

Basically the POSIX tz formats are 3 letters plus the offset. But the offset has to be on the opposite sign. Hence why ["sys.tz_spec", "<+05>5"] worked for you. Just use that one.

That's the answer i was looking for! thanks again!