From b312f226b4cdf279e296d3958aac60b23ae82301 Mon Sep 17 00:00:00 2001
From: phaseloop <90922095+phaseloop@users.noreply.github.com>
Date: Sat, 24 Jan 2026 14:22:01 +0200
Subject: [PATCH] Cut NRF52 bluetooth power usage (#8992)

* Improve NRF52 bluetooth power efficiency

* test T114 bad LFXO

* T1000 test

* force BLE param negotiation

* stash

* NRF52 bluetooth small cleanup

* fix potential connectivity issues

* lower BLE min interval to make iOS happy

* remove slave latency negotation

* add BLE issue comment

* code format

* Revert "code format"

This reverts commit 1f92b09d08cde52cf61f115a6335dfce12ad9ffd.

* remove LFCLK debug info

* Fix

---------

Co-authored-by: Ben Meadors <benmmeadors@gmail.com>
---
 src/platform/nrf52/NRF52Bluetooth.cpp | 35 +++++++++++++++++++++------
 1 file changed, 28 insertions(+), 7 deletions(-)

diff --git a/src/platform/nrf52/NRF52Bluetooth.cpp b/src/platform/nrf52/NRF52Bluetooth.cpp
index d41c7ba0e..6a552f236 100644
--- a/src/platform/nrf52/NRF52Bluetooth.cpp
+++ b/src/platform/nrf52/NRF52Bluetooth.cpp
@@ -119,7 +119,7 @@ void startAdv(void)
     Bluefruit.Advertising.addService(meshBleService);
     /* Start Advertising
      * - Enable auto advertising if disconnected
-     * - Interval:  fast mode = 20 ms, slow mode = 152.5 ms
+     * - Interval:  fast mode = 20 ms, slow mode = 417,5 ms
      * - Timeout for fast mode is 30 seconds
      * - Start(timeout) with timeout = 0 will advertise forever (until connected)
      *
@@ -127,7 +127,7 @@ void startAdv(void)
      * https://developer.apple.com/library/content/qa/qa1931/_index.html
      */
     Bluefruit.Advertising.restartOnDisconnect(true);
-    Bluefruit.Advertising.setInterval(32, 244); // in unit of 0.625 ms
+    Bluefruit.Advertising.setInterval(32, 668); // in unit of 0.625 ms
     Bluefruit.Advertising.setFastTimeout(30);   // number of seconds in fast mode
     Bluefruit.Advertising.start(0); // 0 = Don't stop advertising after n seconds.  FIXME, we should stop advertising after X
 }
@@ -243,10 +243,8 @@ int NRF52Bluetooth::getRssi()
 
 // Valid BLE TX power levels as per nRF52840 Product Specification are: "-20 to +8 dBm TX power, configurable in 4 dB steps".
 // See https://docs.nordicsemi.com/bundle/ps_nrf52840/page/keyfeatures_html5.html
-#define VALID_BLE_TX_POWER(x) \
-    ((x) == -20 || (x) == -16 || (x) == -12 || \
-     (x) == -8  || (x) == -4  || (x) == 0  || \
-     (x) == 4  || (x) == 8)
+#define VALID_BLE_TX_POWER(x)                                                                                                    \
+    ((x) == -20 || (x) == -16 || (x) == -12 || (x) == -8 || (x) == -4 || (x) == 0 || (x) == 4 || (x) == 8)
 
 void NRF52Bluetooth::setup()
 {
@@ -283,6 +281,29 @@ void NRF52Bluetooth::setup()
     // Set the connect/disconnect callback handlers
     Bluefruit.Periph.setConnectCallback(onConnect);
     Bluefruit.Periph.setDisconnectCallback(onDisconnect);
+
+    // Do not change Slave Latency to value other than 0 !!!
+    // There is probably a bug in SoftDevice + certain Apple iOS versions being
+    // brain damaged causing connectivity problems.
+
+    // On one side it seems SoftDevice is using SlaveLatency value even
+    // if connection parameter negotation failed and phone sees it as connectivity errors.
+
+    // On the other hand Apple can randomly refuse any parameter negotiation and shutdown connection
+    // even if you meet Apple Developer Guidelines for BLE devices. Because f* you, that's why.
+
+    // While this API call sets preferred connection parameters (PPCP) - many phones ignore it (yeah) and it seems SoftDevice
+    // will try to renegotiate connection parameters based on those values after phone connection.
+    // So those are relatively safe values so Apple braindead firmware won't get angry and at least we may try
+    // to negotiate some longer connection interval to save battery.
+
+    // See https://github.com/meshtastic/firmware/pull/8858 for measurements.  We are dealing with microamp savings anyway so not
+    // worth dying on a hill here.
+
+    Bluefruit.Periph.setConnSlaveLatency(0);
+    // 1.25 ms units - so min, max is 15, 100 ms range.
+    Bluefruit.Periph.setConnInterval(12, 80);
+
 #ifndef BLE_DFU_SECURE
     bledfu.setPermission(SECMODE_ENC_WITH_MITM, SECMODE_ENC_WITH_MITM);
     bledfu.begin(); // Install the DFU helper
@@ -311,7 +332,7 @@ void NRF52Bluetooth::setup()
 void NRF52Bluetooth::resumeAdvertising()
 {
     Bluefruit.Advertising.restartOnDisconnect(true);
-    Bluefruit.Advertising.setInterval(32, 244); // in unit of 0.625 ms
+    Bluefruit.Advertising.setInterval(32, 668); // in unit of 0.625 ms
     Bluefruit.Advertising.setFastTimeout(30);   // number of seconds in fast mode
     Bluefruit.Advertising.start(0);
 }