Bluetooth: controller: CS LLL/HAL: use real nRF54L15 CSTONES/RTT registers

[Copilot]

The Channel Sounding radio HAL used entirely fictional register names (NRF_RADIO->CS.MODE, CS.TONES, CS.PCTPTR, etc.) and MDK macros (RADIO_CS_MODE_MODE_Msk, RADIO_MODE_MODE_Ble_Cs) that do not exist in the Nordic MDK. The presence gate was always 0, making the hardware path dead code and forcing the emulation path on real silicon.

Rewritten to use the actual nRF54L15 RADIO register layout verified against MDK revision 18da0cc.

HAL presence gate

• Gate on RADIO_CHANNELSOUNDING / RADIO_CSTONES_MODE_TPM_Msk (real MDK symbols) instead of non-existent macros

HAL API redesign (radio_cs.h, radio_cs.c)

• Removed fictional APIs: radio_cs_mode_set(), radio_cs_tone_set(), radio_cs_antenna_set(), radio_cs_pct_buffer_set(), radio_cs_rtt_timestamp_get(), radio_cs_pct_get()
• Added real-hardware APIs using NRF_RADIO->CSTONES.* and NRF_RADIO->RTT.*:
  • radio_cs_cstones_config() — CSTONES.MODE TPM/TFM, NUMSAMPLES, DOWNSAMPLE
  • radio_cs_rtt_config() — RTT.CONFIG EN/ROLE/NUMSEGMENTS/EFSDELAY
  • radio_cs_rtt_segments_set() — RTT.SEGMENT01..67
  • radio_cs_next_freq_set() — CSTONES.NEXTFREQUENCY for T_FCS PLL pre-tune
  • radio_cs_cstones_start() — TASKS_CSTONESSTART
  • radio_cs_pct16_get() — single-register PCT16 read (no DMA)
  • radio_cs_cstones_end_clear()/is_set() — EVENTS_CSTONESEND

LLL step sequencing (lll_cs.c)

• Hardware path: CS_SYNC PDU END → isr_step → TASKS_CSTONESSTART → isr_cstones_end (EVENTS_CSTONESEND) → capture PCT16 → advance with NEXTFREQUENCY pre-tune
• Emulation path: strictly behind !radio_cs_is_supported() — fabricated RTT/IQ for BabbleSim only
• Removed pct_scratch DMA buffer from struct lll_cs (real HW has no PCT EasyDMA)

Channel shuffle (ull_cs.c)

• Documented that the LCG Fisher-Yates shuffle is a BabbleSim placeholder, not the spec CS channel selection algorithm

/* Real hardware step sequence (simplified): */
radio_cs_cstones_config(tpm_en, tfm_en, 80, phy_2m);
radio_cs_rtt_config(true, role_reflect, num_seg, efs_delay);
radio_cs_next_freq_set(next_step_channel);
/* ... CS_SYNC PDU exchange via standard packet engine ... */
radio_cs_cstones_start();              /* TASKS_CSTONESSTART */
/* ISR on EVENTS_CSTONESEND: */
radio_cs_pct16_get(&iq_sample);        /* Read PCT16 register */

Original prompt

Overview

Add LE Channel Sounding feature support to the open source Zephyr Bluetooth Controller implementation. The Zephyr Bluetooth Host already has LE Channel Sounding support with samples under samples/bluetooth/channel_sounding.

Specification Reference

Implement LE Channel Sounding according to BLUETOOTH CORE SPECIFICATION Version 6.2 | Vol 6, Part B Section 4.5.18 Channel Sounding.

Requirements

1. HCI Commands and Events

Add the required new HCI Commands and Events for LE Channel Sounding as specified in the Bluetooth Core Specification.

2. PDU Structures

Implement PDU (Protocol Data Unit) structures needed for Channel Sounding procedures.

3. ULL (Upper Link Layer) Implementation

• Add ULL interfaces for Channel Sounding
• Implement required data structures for the design
• Design and implement the necessary state machines

4. Link Layer Control Procedures

Implement Link Layer Control Procedures for Channel Sounding, including unit tests. Refer to the following message sequence charts from BLUETOOTH CORE SPECIFICATION Version 6.2 | Vol 6, Part D:

• Section 6.34: Channel Sounding setup phase
• Section 6.35: Channel Sounding started by Central in initiator role
• Section 6.36: Channel Sounding started by Peripheral in reflector role
• Section 6.37: Channel Sounding started by Central, rejected by Peripheral
• Section 6.38: Channel Sounding configuration removal during an active CS procedure

5. LLL (Lower Link Layer) Implementation

Implement LLL (Lower Link Layer) components that use the Radio HAL (Hardware Abstraction Layer) for Channel Sounding operations.

6. Unit Tests

Add comprehensive unit tests for the Control Procedures to ensure correct implementation of all Channel Sounding scenarios.

Expected Deliverables

1. HCI command and event handlers
2. PDU structure definitions
3. ULL interface implementation with data structures
4. Link Layer Control Procedure implementation
5. LLL implementation using Radio HAL
6. Unit tests for Control Procedures
7. Documentation updates as needed

Notes

• Ensure compatibility with existing Bluetooth Host Channel Sounding implementation
• Follow Zephyr coding standards and conventions
• Maintain consistency with existing Bluetooth Controller architecture in Zephyr

This pull request was created from Copilot chat.

---

💬 We'd love your input! Share your thoughts on Copilot coding agent in our 2 minute survey.