From d2e47b79d9a7fbc3b543fe5783e9a7fc5d629676 Mon Sep 17 00:00:00 2001
From: pstruebi <struebin.patrick@gmail.com>
Date: Thu, 30 Apr 2026 17:07:28 +0200
Subject: [PATCH] Apply advertising TX power via Zephyr vendor-specific command
 for Nordic SDC.

---
 src/auracast/multicast.py | 37 ++++++++++++++++++++++++++++++++++++-
 1 file changed, 36 insertions(+), 1 deletion(-)

diff --git a/src/auracast/multicast.py b/src/auracast/multicast.py
index b423f5a..b962492 100644
--- a/src/auracast/multicast.py
+++ b/src/auracast/multicast.py
@@ -49,6 +49,7 @@ import bumble.transport
 import bumble.utils
 from bumble.device import Host, AdvertisingChannelMap
 from bumble.audio import io as audio_io
+from bumble.vendor.zephyr.hci import HCI_Write_Tx_Power_Level_Command
 
 from auracast import auracast_config
 from auracast.utils.read_lc3_file import read_lc3_file
@@ -537,12 +538,46 @@ async def init_broadcast(
         )
         bigs[f'big{i}']['advertising_set'] = advertising_set
         logging.info(
-            'Advertising TX power: requested=%+d dBm, controller selected=%+d dBm (handle=%d)',
+            'Advertising TX power (LE_Set_Ext_Adv_Params): requested=%+d dBm, controller selected=%+d dBm (handle=%d)',
             global_config.advertising_tx_power,
             getattr(advertising_set, 'selected_tx_power', 0),
             i,
         )
 
+        # The Nordic SoftDevice Controller does not honor the per-set
+        # advertising_tx_power passed in HCI_LE_Set_Extended_Advertising_Parameters
+        # (it returns the compile-time CONFIG_BT_CTLR_TX_PWR_* value regardless).
+        # Apply the requested level via the Zephyr Vendor-Specific HCI command
+        # Write_Tx_Power_Level (opcode 0xFC0E), which the SDC honors per
+        # advertising handle. The SDC clamps the value to the nearest supported
+        # hardware step (max bounded by CONFIG_BT_CTLR_TX_PWR_PLUS_8).
+        try:
+            adv_handle = getattr(advertising_set, 'advertising_handle', i)
+            response = await device.send_command(
+                HCI_Write_Tx_Power_Level_Command(
+                    handle_type=HCI_Write_Tx_Power_Level_Command.TX_POWER_HANDLE_TYPE_ADV,
+                    connection_handle=adv_handle,
+                    tx_power_level=global_config.advertising_tx_power,
+                )
+            )
+            rp = getattr(response, 'return_parameters', None)
+            status = getattr(rp, 'status', 0xFF) if rp is not None else 0xFF
+            selected = getattr(rp, 'selected_tx_power_level', None) if rp is not None else None
+            if status == 0 and selected is not None:
+                logging.info(
+                    'Advertising TX power (VS Write_Tx_Power_Level): requested=%+d dBm, controller selected=%+d dBm (handle=%d)',
+                    global_config.advertising_tx_power,
+                    selected,
+                    adv_handle,
+                )
+            else:
+                logging.warning(
+                    'VS Write_Tx_Power_Level failed: status=0x%02X handle=%d requested=%+d dBm',
+                    status, adv_handle, global_config.advertising_tx_power,
+                )
+        except Exception as e:
+            logging.warning('VS Write_Tx_Power_Level not supported by controller: %s', e)
+
         logging.info('Start Periodic Advertising')
         await advertising_set.start_periodic()