Channel Sounding and Sub mode

Hi,

I have a simple question about Bluetooth Channel Sounding:

Question: If I use BT_CONN_LE_CS_MAIN_MODE_3 as main mode (PBR + RTT), does it make sense to use sub mode like BT_CONN_LE_CS_SUB_MODE_2 (or any except BT_CONN_LE_CS_SUB_MODE_UNUSED)? How does this all work?

My setup:

.main_mode_type = BT_CONN_LE_CS_MAIN_MODE_3,  // PBR + RTT
.sub_mode_type = BT_CONN_LE_CS_SUB_MODE_2,    // RTT only
.min_main_mode_steps = 2,
.max_main_mode_steps = 5,

What I think it does:

  • Main mode = most T_FCS steps use Mode 3
  • Sub mode = sometimes use Mode 2 between main mode steps
  • "Sometimes" means: do 2-5 main steps, then 1 sub step, then repeat?

Questions:

  1. Do I understand this correctly?
  2. How does the CS system know when to use sub mode?

Thank you.

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