For improving my data trouchput (both directions, using »Write without response« and »Notification« like e.g. nRF Uart Example do9, I'd performed some tests regarding the connection parameters (especially connection interval) with different Android devices.
On the Android side, I tested with my own tiny app but also with Nordic nRF Master Control Panel (Mcp).
IMHO, the test results are very surprising. They may hardly depend upon BT hardware (mostly Broadcom versus Qualcomm) and also on the installed Android version (4.3 versus 4.4.2 versus 4.4.3 and even Android stock release versus Cyanogen).
To get the fastest connection intervall, I'd set on my nRF51822 side both min and max to 7,5ms:
#define MIN_CONN_INTERVAL 6 ///< 7,5 ms
#define MAX_CONN_INTERVAL 6 ///< 7,5 ms
(I also tried Min=11,25 ms and Max= 15 ms like the Nordic Bootloader example do.) To verify the applied setting, I'd added some debug output to my code, were I hook:
- the ble event BLE_GAP_EVT_CONNECTED
- the ble event BLE_GAP_EVT_CONN_PARAM_UPDATE
- ble_conn_params_init_t.evt_handler for BLE_CONN_PARAMS_EVT_FAILED
My tested Android devices are mainly:
- Samsung Note SM-P605 with Android 4.3 stock release
- Sony Xperia Z with both Android 4.3 stock release
- Sony Xperia Z with both Android 4.4.2 stock release
- Htc One with Android 4.4.2 stock release
- Samsung Note GT-N8000 with Android 4.4.2 stock release (Broadcom BCM4334)
- Nexus 7 2012 with Android 4.4.3 stock release (Broadcom BCM4330)
- Nexus 7 2013 with Android 4.4.3 stock release (Qualcomm Atheros WCN3660)
- Nexus 7 2013 with Android 4.4.3 cyanogenmod (Qualcomm Atheros WCN3660)
When connecting, on the most devices I'll get a BLE_GAP_EVT_CONNECTED with a connection interval of 48,75 ms and afterwards a BLE_GAP_EVT_CONN_PARAM_UPDATE with my desired 7,5 ms.
A (positive) exception is the (2) Sony Xperia with Android 4.3, were I get 7,5 ms upon connect (without BLE_GAP_EVT_CONN_PARAM_UPDATE).
The best throughput, I measured with (4) Htc One and (8) Nexus 7 2013 with cyanogenmod at about 8-10 kB/s in both directions (don't checked the number of packets per event until now).
But there are also some negative exceptions:
(1) Samsung Note SM-P605
Ok, the SM-P605 central connects with 48,75 ms. But it stubbornly refuses my peripheral's connection parameter update request (were I ask for 7,5 ms). My debug output:
INFO : Connected
TRACE: Ble event id=10h len=22, name=GAP_EVT_CONNECTED, range=Gap event
TRACE: Connect: peer=0 76-5D-C2-19-57-80, irk_match=0, irk_match_idx=0
TRACE: ConnParams: minInterv = 39 = 48,75ms, maxInterv = 39 = 48,75ms, slaveLatency = 0, connSupTimeout = 700 = 7000ms
TRACE: Ble event id=12h len=14, name=GAP_EVT_CONN_PARAM_UPDATE, range=Gap event
TRACE: ConnParams: minInterv = 39 = 48,75ms, maxInterv = 39 = 48,75ms, slaveLatency = 0, connSupTimeout = 700 = 7000ms
TRACE: Ble event id=12h len=14, name=GAP_EVT_CONN_PARAM_UPDATE, range=Gap event
TRACE: ConnParams: minInterv = 39 = 48,75ms, maxInterv = 39 = 48,75ms, slaveLatency = 0, connSupTimeout = 700 = 7000ms
TRACE: Ble event id=12h len=14, name=GAP_EVT_CONN_PARAM_UPDATE, range=Gap event
TRACE: ConnParams: minInterv = 39 = 48,75ms, maxInterv = 39 = 48,75ms, slaveLatency = 0, connSupTimeout = 700 = 7000ms
WARN : CONN_PARAMS_EVT_FAILED - Connection Parameter Update Request failed, but we'll decide to keep connected.
→ And now the question: Does anyone noticed a behavior like this? How could I motivate this device to accept a faster connection interval than 48,75 ms ?
I got the same if I try e.g. min=30 ms max=47,5 ms - for every range were the max value is lower than 48,75 ms. Looks like the device won't be communicate faster than 48,75 ms. When I try with e.g. with min=200 ms max=250 ms, the negotiation succeeds:
INFO : Connected
TRACE: Ble event id=10h len=22, name=GAP_EVT_CONNECTED, range=Gap event
TRACE: Connect: peer=0 76-5D-C2-19-57-80, irk_match=0, irk_match_idx=0
TRACE: ConnParams: minInterv = 39 = 48,75ms, maxInterv = 39 = 48,75ms, slaveLatency = 0, connSupTimeout = 700 = 7000ms
TRACE: Ble event id=12h len=14, name=GAP_EVT_CONN_PARAM_UPDATE, range=Gap event
TRACE: ConnParams: minInterv = 198 = 247,50ms, maxInterv = 198 = 247,50ms, slaveLatency = 0, connSupTimeout = 2000 = 20000ms
INFO : Connection Parameter Update Request succeeded.
I also tried to put my desired connection interval range into the advertising data like this:
ble_advdata_conn_int_t connParams;
connParams.min_conn_interval = 6;
connParams.max_conn_interval = 9;
advdata.p_slave_conn_int = &connParams;
scanrsp.p_slave_conn_int = &connParams;
and I'd been happy to see that an my Android device running Mcp:
But unfortunately, my Android device seems to ignore this information completely when connecting.
