HCIHandler*: Tuning LE scan + connection parameters for higher performance (stable @ 15ms scan + connect)

commit a2096bf3baf8fb5fc8ed37ce4bdb1ec1112b6e8d increased the connection interval max from 20ms -> 30ms,
which caused a performance loss of about magnitude 2 (took > 2 as long as before).

Tested fixed 15ms connection interval on CSR and Raspi adapter, so far so good.

Notable: Android starts even with just below 10ms and Apple at 11ms (accessoir) or 15ms (default min).

Performance w/ 15ms is excellent.

4 files changed, 16 insertions, 16 deletions

diff --git a/api/direct_bt/DBTAdapter.hpp b/api/direct_bt/DBTAdapter.hpp
index 763a4454..273887da 100644
--- a/api/direct_bt/DBTAdapter.hpp
+++ b/api/direct_bt/DBTAdapter.hpp
@@ -372,16 +372,16 @@ namespace direct_bt {
              * @param address
              * @param address_type
              * @param ctype
-             * @param conn_interval_min in units of 1.25ms, default value 16 for 20ms; Value range [6 .. 3200] for [7.5ms .. 4000ms]
-             * @param conn_interval_max in units of 1.25ms, default value 24 for 30ms Value range [6 .. 3200] for [7.5ms .. 4000ms]
+             * @param conn_interval_min in units of 1.25ms, default value 12 for 15ms; Value range [6 .. 3200] for [7.5ms .. 4000ms]
+             * @param conn_interval_max in units of 1.25ms, default value 12 for 15ms; Value range [6 .. 3200] for [7.5ms .. 4000ms]
              * @param conn_latency slave latency in units of connection events, default value 0; Value range [0 .. 0x01F3].
              * @param supervision_timeout in units of 10ms, default value >= 10 x conn_interval_max, we use HCIConstInt::LE_CONN_MIN_TIMEOUT_MS minimum; Value range [0xA-0x0C80] for [100ms - 32s].
              * @return true if the device was already added or has been newly added to the adapter's whitelist.
              */
             bool addDeviceToWhitelist(const EUI48 &address, const BDAddressType address_type,
                                       const HCIWhitelistConnectType ctype,
-                                      const uint16_t conn_interval_min=16, const uint16_t conn_interval_max=24,
-                                      const uint16_t conn_latency=0, const uint16_t supervision_timeout=getHCIConnSupervisorTimeout(0, 30));
+                                      const uint16_t conn_interval_min=12, const uint16_t conn_interval_max=12,
+                                      const uint16_t conn_latency=0, const uint16_t supervision_timeout=getHCIConnSupervisorTimeout(0, 15)) noexcept;
 
 
             /** Remove the given device from the adapter's autoconnect whitelist. */
diff --git a/api/direct_bt/DBTDevice.hpp b/api/direct_bt/DBTDevice.hpp
index 8f130b30..7d96700f 100644
--- a/api/direct_bt/DBTDevice.hpp
+++ b/api/direct_bt/DBTDevice.hpp
@@ -238,15 +238,15 @@ namespace direct_bt {
              *
              * @param le_scan_interval in units of 0.625ms, default value 24 for 15ms; Value range [4 .. 0x4000] for [2.5ms .. 10.24s]
              * @param le_scan_window in units of 0.625ms, default value 24 for 15ms; Value range [4 .. 0x4000] for [2.5ms .. 10.24s]. Shall be <= le_scan_interval
-             * @param conn_interval_min in units of 1.25ms, default value 16 for 20ms; Value range [6 .. 3200] for [7.5ms .. 4000ms]
-             * @param conn_interval_max in units of 1.25ms, default value 24 for 30ms Value range [6 .. 3200] for [7.5ms .. 4000ms]
+             * @param conn_interval_min in units of 1.25ms, default value 12 for 15ms; Value range [6 .. 3200] for [7.5ms .. 4000ms]
+             * @param conn_interval_max in units of 1.25ms, default value 12 for 15ms; Value range [6 .. 3200] for [7.5ms .. 4000ms]
              * @param conn_latency slave latency in units of connection events, default value 0; Value range [0 .. 0x01F3].
              * @param supervision_timeout in units of 10ms, default value >= 10 x conn_interval_max, we use HCIConstInt::LE_CONN_MIN_TIMEOUT_MS minimum; Value range [0xA-0x0C80] for [100ms - 32s].
              * @return HCIStatusCode::SUCCESS if the command has been accepted, otherwise HCIStatusCode may disclose reason for rejection.
              */
             HCIStatusCode connectLE(const uint16_t le_scan_interval=24, const uint16_t le_scan_window=24,
-                                    const uint16_t conn_interval_min=16, const uint16_t conn_interval_max=24,
-                                    const uint16_t conn_latency=0, const uint16_t supervision_timeout=getHCIConnSupervisorTimeout(0, 30));
+                                    const uint16_t conn_interval_min=12, const uint16_t conn_interval_max=12,
+                                    const uint16_t conn_latency=0, const uint16_t supervision_timeout=getHCIConnSupervisorTimeout(0, 15));
 
             /**
              * Establish a HCI BDADDR_BREDR connection to this device.
diff --git a/api/direct_bt/DBTManager.hpp b/api/direct_bt/DBTManager.hpp
index a570a23d..10752a89 100644
--- a/api/direct_bt/DBTManager.hpp
+++ b/api/direct_bt/DBTManager.hpp
@@ -314,15 +314,15 @@ namespace direct_bt {
              * @param dev_id
              * @param address
              * @param address_type
-             * @param conn_interval_min in units of 1.25ms, default value 16 for 20ms; Value range [6 .. 3200] for [7.5ms .. 4000ms]
-             * @param conn_interval_max in units of 1.25ms, default value 24 for 30ms Value range [6 .. 3200] for [7.5ms .. 4000ms]
+             * @param conn_interval_min in units of 1.25ms, default value 12 for 15ms; Value range [6 .. 3200] for [7.5ms .. 4000ms]
+             * @param conn_interval_max in units of 1.25ms, default value 12 for 15ms; Value range [6 .. 3200] for [7.5ms .. 4000ms]
              * @param conn_latency slave latency in units of connection events, default value 0; Value range [0 .. 0x01F3].
              * @param supervision_timeout in units of 10ms, default value >= 10 x conn_interval_max, we use HCIConstInt::LE_CONN_MIN_TIMEOUT_MS minimum; Value range [0xA-0x0C80] for [100ms - 32s].
              * @return
              */
             bool uploadConnParam(const int dev_id, const EUI48 &address, const BDAddressType address_type,
-                                 const uint16_t conn_interval_min=16, const uint16_t conn_interval_max=24,
-                                 const uint16_t conn_latency=0, const uint16_t supervision_timeout=getHCIConnSupervisorTimeout(0, 30)) noexcept;
+                                 const uint16_t conn_interval_min=12, const uint16_t conn_interval_max=12,
+                                 const uint16_t conn_latency=0, const uint16_t supervision_timeout=getHCIConnSupervisorTimeout(0, 15)) noexcept;
 
             /**
              * Returns true, if the adapter's device is already whitelisted.
diff --git a/api/direct_bt/HCIHandler.hpp b/api/direct_bt/HCIHandler.hpp
index 8b66464e..94d146a1 100644
--- a/api/direct_bt/HCIHandler.hpp
+++ b/api/direct_bt/HCIHandler.hpp
@@ -351,8 +351,8 @@ namespace direct_bt {
              * @param own_mac_type
              * @param le_scan_interval in units of 0.625ms, default value 24 for 15ms; Value range [4 .. 0x4000] for [2.5ms .. 10.24s]
              * @param le_scan_window in units of 0.625ms, default value 24 for 15ms; Value range [4 .. 0x4000] for [2.5ms .. 10.24s]. Shall be <= le_scan_interval
-             * @param conn_interval_min in units of 1.25ms, default value 16 for 20ms; Value range [6 .. 3200] for [7.5ms .. 4000ms]
-             * @param conn_interval_max in units of 1.25ms, default value 24 for 30ms Value range [6 .. 3200] for [7.5ms .. 4000ms]
+             * @param conn_interval_min in units of 1.25ms, default value 12 for 15ms; Value range [6 .. 3200] for [7.5ms .. 4000ms]
+             * @param conn_interval_max in units of 1.25ms, default value 12 for 15ms; Value range [6 .. 3200] for [7.5ms .. 4000ms]
              * @param conn_latency slave latency in units of connection events, default value 0; Value range [0 .. 0x01F3].
              * @param supervision_timeout in units of 10ms, default value >= 10 x conn_interval_max, we use HCIConstInt::LE_CONN_MIN_TIMEOUT_MS minimum; Value range [0xA-0x0C80] for [100ms - 32s].
              * @return
@@ -361,8 +361,8 @@ namespace direct_bt {
                                         const HCILEPeerAddressType peer_mac_type=HCILEPeerAddressType::PUBLIC,
                                         const HCILEOwnAddressType own_mac_type=HCILEOwnAddressType::PUBLIC,
                                         const uint16_t le_scan_interval=24, const uint16_t le_scan_window=24,
-                                        const uint16_t conn_interval_min=16, const uint16_t conn_interval_max=24,
-                                        const uint16_t conn_latency=0, const uint16_t supervision_timeout=getHCIConnSupervisorTimeout(0, 30)) noexcept;
+                                        const uint16_t conn_interval_min=12, const uint16_t conn_interval_max=12,
+                                        const uint16_t conn_latency=0, const uint16_t supervision_timeout=getHCIConnSupervisorTimeout(0, 15)) noexcept;
 
             /**
              * Establish a connection to the given BREDR (non LE).