Why is the HFCLK necessary for the DTM module?

RE: Why is the HFCLK necessary for the DTM module?

Elias — Thu, 16 Aug 2018 00:55:21 GMT

Question edited after I've done more experimenting.

RE: Why is timer_init() necessary for the DTM module?

Elias — Wed, 15 Aug 2018 20:06:38 GMT

The timer_init() is apparently necessary even when I comment-out line 881-889. I'm also using dtm_constant_carrier(), so there shouldn't be any real "packets".

RE: Why is timer_init() necessary for the DTM module?

Einar Thorsrud — Wed, 15 Aug 2018 05:27:19 GMT

Hi,

You can see from the implementation in ble_dtm.c that the timer is used to transmit packets with the correct delay between each packet (line 881-889 in ble_dtm.c in SDK 15.0.0).

Update: I forgot the most obvious reason for requiring the HFCLK in my original answer, which is that requesting the HFCLK causes the crystal oscillator (HFXC) to run, which is required in order to get an accurate clock for using the radio. The HFINT oscillator is way too inaccurate for using the radio (worst case ±6 %). The SoftDevice normally starts the HFXC before it uses the radio, but as the DTM example handles the radio directly, it must also make sure to enable the clock.