Getting Time Zone and Daylight Savings info out of CTS

RE: Getting Time Zone and Daylight Savings info out of CTS

Mike Austin (LPI) — Sun, 15 Jan 2023 23:21:47 GMT

Hi Steven,

Have a look on my repo here: https://github.com/maustin-redant/local_time_info

That has patch files that will update your version of NCS with the API's you need to access the local time info.

If you need further details on the call backs, etc I wrote to actually get the info I wanted, let me know

Cheers,

Mike

RE: Getting Time Zone and Daylight Savings info out of CTS

setenv — Sun, 15 Jan 2023 15:56:28 GMT

Hi Mike, I am facing the same issue and it looks like your way to solve it makes most sense to get the DST out. Is there a way you could share some of this code?

Best regarsd,

Steven

RE: Getting Time Zone and Daylight Savings info out of CTS

Mike Austin (LPI) — Thu, 04 Aug 2022 05:44:46 GMT

Hi Simon,

Thanks for that - very helpful :-)

OK, I *think* I've got it all working. I had to hack about with the cts_client.c and cts_client.h files in the nrf folder, which of course means if I ever update my SDK all that gets wiped. So, at some point, I might attempt to push those changes up to GitHub for them to be checked over and potentially added to the SDK in a future release.

I've done all my testing using the nRF Connect For Desktop App, and used the setup from the peripheral_cts_client example. I then added a Local Time characteristic, so I could change the time zone and dst figures and confirm these are being captured by my client device - which they are.

From my read of the spec, the Local Time info doesn't have notify capabilities. I believe that is all bundled up in the Current Time info, under the bt_cts_adjust_reason structure. If timezone or dst status changes, these are notified via the Current Time notification, and then I guess its up to the client to decide if it needs to grab and update the Local Time characteristic info.

Thanks for you help on this. I think we can mark this one as "solved" now

Cheers,

Mike

RE: Getting Time Zone and Daylight Savings info out of CTS

Simon — Fri, 29 Jul 2022 23:06:41 GMT

You are right, similar to the nRF5 SDK, the nRF Connect SDK has not implemented capablitiy to read the Local Time Information Characteristic (LTIC). Like Terje explains here mktime() in nordic calendar example is not taking local time into account?

It seems like your thinking is correct, regarding how to read the LTIC. Let me go through what I think needs to be done

I think you'll need to do the following:

1. Define the LTIC UUID

Do it similar to how it's done for the Current Time Characteristic (CTC): https://github.com/nrfconnect/sdk-zephyr/blob/main/include/zephyr/bluetooth/uuid.h#L864-L872

Call it BT_UUID_CTS_LOCAL_TIME_INFORMATION and use the UUID 0x2A0F (I got this value from the nRF5 SDK documentation).

2. Modify the bt_cts_client struct

Add a handle for the LTIC similar for how it's done for the CTC: https://github.com/nrfconnect/sdk-nrf/blob/v2.0.2/include/bluetooth/services/cts_client.h#L82-L83

You can call the LTIC handle field handle_lti

I'm not sure if the LTIC has notify-capabilities, in that case add a CCCD handle as well.

3. Assign the handle

In the function bt_cts_handles_assign(), copy these lines and do the same thing for the LTIC. You will end up with assigning the LTIC handle to cts_c->handle_lti. If the LTIC has notify-capablities, copy these lines as well and modify them accordingly.

4. Create a function bt_cts_read_local_time()

Copy the function bt_cts_read_current_time() and modify it to use the LTIC handle instead.

If the LTIC has notify-capabilities, copy the function bt_cts_subscribe_current_time() as well and modify it accordingly.

Also you should check if the iPhone you're getting the CTS info from actually has the LTIC characteristics, if not you will not be able to read it.

Be aware that I have not tested this myself, and I might have forgotten something. I just looked quickly into it and wrote down how I understood it before I now take vacation for two weeks.

I will make sure someone else takes over and watches this case, in case you got any follow-up questions.

Best regards,

Simon

RE: Getting Time Zone and Daylight Savings info out of CTS

Mike Austin (LPI) — Wed, 27 Jul 2022 04:07:56 GMT

Hi Simon,

Still struggling with this (getting the Local Time info out of the CTS).

From the looks of the nRF5 SDK code, the process to get the Current Time info out of the CTS involves:

1. A call to err = bt_cts_read_current_time(&cts_c, func); Here, the func is the callback function that you can define, and that is called when the read operation is completed

2. The bt_cts_read_current_time call then sets up a bunch of parameters, via:

cts_c->read_cb = func;

cts_c->read_params.func = bt_cts_read_callback;

cts_c->read_params.handle_count = 1;

cts_c->read_params.single.handle = cts_c->handle_ct;cts_c->read_params.single.offset = 0;

Not sure what this is all doing, but I'm guessing its setting things up so that the GATT read that comes next knows what characteristic it needs to access. The bt_cts_read_callback function listed amongst all of this seems to do a bunch of data decoding, and validation, and I'm guessing this gets called once the next step below has been implemented.

3. It then makes a call to err = bt_gatt_read(cts_c->conn, &cts_c->read_params); which looks to be Nordics general GATT read API

What I'm trying to do is work out what I need to add to my code, along the lines of the above, to enable me to access the Local Time info.

I'm thinking I need to define my own bt_cts_read_local_time() API (to emulate the bt_cts_read_current_time(&cts_c, func) one from Nordic), and then set up the parameters listed above to access the Local Time info characteristic, and include my own version of the bt_cts_read_callback API, which will no doubt need my own data decoding and data validation API's. I can then just make the same call to bt_gatt_read and I "should" now have the Local Time info.

Does that sound right to you?

Seems weird that Nordic wouldn't have done the heavy lifting and write a bunch of API's to extract the Local Time info as well as the Current Time info, but c'est la vie!

Cheers,

Mike

RE: Getting Time Zone and Daylight Savings info out of CTS

Mike Austin (LPI) — Sun, 24 Jul 2022 09:36:31 GMT

Yep, happy to close off Converting local time from CTS to UTC time

Still not sure how to get the Time Zone and DST info out of the CTS though

Cheers,

Mike

RE: Getting Time Zone and Daylight Savings info out of CTS

Simon — Fri, 22 Jul 2022 10:14:15 GMT

It seems like you found a solution in Converting local time from CTS to UTC time. Should we close this one?

RE: Getting Time Zone and Daylight Savings info out of CTS

Mike Austin (LPI) — Thu, 21 Jul 2022 10:51:01 GMT

[quote userid="72692" url="~/f/nordic-q-a/90191/getting-time-zone-and-daylight-savings-info-out-of-cts/378037"]Next, you would then need to include the Local Time Information characterstic, and use that to get the Time zone field and the DST offset field. [/quote]

That's the issue. The Nordic API's only extract the Current Time characteristic, and don't include the Local Time characteristic. And I can't work out how I can get that info myself.

My code that extracts the Current Time characteristic is based on that Peripheral CTS Client example.

I "think" all I need to do is read a Gatt characteristic, and use the Local Time characteristic handle to reference that, but I'm floundering around trying to work out how to do that.

BTW - think I've nailed the Local->UTC conversion thing myself.

Cheers,

Mike

RE: Getting Time Zone and Daylight Savings info out of CTS

Simon — Thu, 21 Jul 2022 10:11:06 GMT

I looked into this.

Looking at this document: Current Time Service.

I see that the CTS Service can contain both a Current Time characterstic and a Local Time information characterstic.

The Current Time characteristic contains the time local time, adjusted for DST and time zone. See 3.1.1 in the attached document:

"The date and time values returned shall be the local date and time of the server device (the time the server device would display to the user, which is normally the correct time for the location adjusted for time zone and DST)."

Next, you would then need to include the Local Time Information characterstic, and use that to get the Time zone field and the DST offset field.

Then you can get the UTC time by subtracting the DST offset field and Time zone field from the current local time you got from the Current Time characteristic.

I've not gone into the speficics of how to do this, but try to check out the Peripheral CTS client sample, it demonstrates how to get all these fields: Peripheral CTS Client

Best regards,

Simon

RE: Getting Time Zone and Daylight Savings info out of CTS

Simon — Thu, 21 Jul 2022 09:23:06 GMT

[quote user="Mike Austin (LPI)"]

Yep, happy to bundle the two issues together.

I just thought that someone might have done the heavy lifting on the UTC conversion before.

[/quote]

^Quote from Converting local time from CTS to UTC time

Yeah I would think so myself, but I tried to search through the entire database and all I found was this ticket (nRF5 SDK): mktime() in nordic calendar example is not taking local time into account?, not sure if that will be of much help.

I'll investigate myself and see if I can figure out how to go about this