Deafult Tx Power changed to 0dBm in DTM library since SDK10

[endnode]

Dear Nordic team,

Beside other persistent issues with your proprietary DTM command for setting Tx Power (see here and here) I've found that default Tx Power in ble_dtm module was changed from max (+4dBm) to 0dBm in SDK10 (and kept in SDK11). See line #30 of /components/ble/ble_dtm/ble_dtm.h

#define DEFAULT_TX_POWER                RADIO_TXPOWER_TXPOWER_0dBm      /**< Default Transmission power using in the DTM module. */

Isn't it in contradiction with BT Core spec (at least with v4.0) where it is required to run DTM at maximum output power? This is my understanding from BT SIG Core 4.0 Volume 6 (Core System Package [Low Energy Controller Volume]) Part F (Direct Test Mode) Section 2.1 (Test Sequences) that DTM commands issued over "DTM Uart" and "HCI" are equal. Then Host Control Interface Functional Specification (Volume 2 Part E Section 7) says that commands should be performed at maximum transmit power, e.g. see this example in paragraph 7.8.29:

What was rationale behind this change (and could it be reverted back?;).

Thanks Jan

[Hung Bui]

Hi Jan,

Could you point me into the place in BT Core spec that requires maximum output power when doing DTM ? I actually couldn't find it.

[endnode]

Hi Hang Bui,

I've updated the question because I cannot put attachment to the comment.

Thanks Jan

[Hung Bui]

Hi Jan,

Thanks for pointing out.

I believe it's the maximum output power that the application plans to use. It's not the maximum the radio are capable but the maximum that will be used. Same applied for the frequencies, the radio can operate outside of 2480MHz but we don't have to test that.

We see most of customers don't use +4dBm for transmission and I assume that's the reason we changed the default DEFAULT_TX_POWER. You, of course, can switch it back to +4dBm

[endnode]

Hi Hung Bui,

Well this is HCI layer specification, it explicitly speaks about "Controller" and there is really no sign of the application at this stage so it's hard to imagine this interpretation. What if is general multi-app HW and stack being tested/certified? I believe purpose of DTM is quite different then certification of device capabilities in the limits of intended application...

Cheers Jan

[Hung Bui]

Hi again Jan,

I understand that the command is from the host to the controller. But in the end, the DTM is to verifiy of the functionalities of a product. I don't see the point of testing something that the product doesn't offer. I just double checked with one of our hardware guys and he said we changed it to 0dBm not by accident and don't think we will change it back to 4dBm.

But as mentioned, you can easy change it back to 4dBm if you like.