nRF52 SDK 15 iOS -> low data rate

RE: nRF52 SDK 15 iOS -> low data rate

BitsAndBytes — Wed, 29 May 2019 23:01:00 GMT

Ok, have the answer now (thanks to Daniel Veilleux !)

The original issue was due to me setting:

bleCfg.conn_cfg.params.gap_conn_cfg.event_length = BLE_GAP_EVENT_LENGTH_DEFAULT;

BLE_GAP_EVENT_LENGTH_DEFAULT is too small for Extended Data Length, therefore I was getting errors in the log when connecting but didn't notice:

<error> nrf_ble_gatt: sd_ble_gap_data_length_update() (request) on connection 0x1 returned NRF_ERROR_RESOURCES.

<error> nrf_ble_gatt: The requested TX/RX packet length is too long by 95/95 octets.

<info> app: NRF_BLE_SCAN_EVT_CONNECTED

So the fix is setting event_length to something larger, for example:

bleCfg.conn_cfg.params.gap_conn_cfg.event_length = BLE_GAP_EVENT_LENGTH_DEFAULT * 10;

This fixed the low data rate issue.

RE: nRF52 SDK 15 iOS -> low data rate

BitsAndBytes — Wed, 29 May 2019 13:35:37 GMT

Urghh. After further testing... commenting out the lines above is a no go since now I'm getting errors related to not enough memory for my characteristics (characteristic_add --> error 4).

Anyone with a fix/knowledge why the above code effects throughput?

RE: nRF52 SDK 15 iOS -> low data rate

BitsAndBytes — Wed, 22 May 2019 16:16:22 GMT

Just found the issue. Not sure why yet, but after removing the following lines of code in my bleStackInit function I'm able to achieve ~264kbps (~33kBytes/sec).

// Setup memory for a max sized attribute table

memset(&bleCfg, 0, sizeof(bleCfg));

bleCfg.gatts_cfg.attr_tab_size.attr_tab_size = BLE_GATTS_ATTR_TAB_SIZE_DEFAULT + 512;

err_code = sd_ble_cfg_set(BLE_GATTS_CFG_ATTR_TAB_SIZE, &bleCfg, ramStart);

APP_ERROR_RESET(err_code);

// Setup memory for a max number of connections

memset(&bleCfg, 0, sizeof(bleCfg));

bleCfg.conn_cfg.params.gap_conn_cfg.conn_count = (peripheralConnections + centralConnections);

bleCfg.conn_cfg.params.gap_conn_cfg.event_length = BLE_GAP_EVENT_LENGTH_DEFAULT;

bleCfg.conn_cfg.conn_cfg_tag = APP_BLE_CONN_CFG_TAG;

err_code = sd_ble_cfg_set(BLE_CONN_CFG_GAP, &bleCfg, ramStart);

APP_ERROR_RESET(err_code);

If anyone has insight on the 'why', please share.

RE: nRF52 SDK 15 iOS -> low data rate

BitsAndBytes — Tue, 21 May 2019 20:31:15 GMT

Thanks for the response.

I'd be happy with 400kbps but still hitting the 10kbps (~1250 Bytes/sec) wall. Can you help me achieve the 400kbps?

RE: nRF52 SDK 15 iOS -> low data rate

run_ar — Tue, 21 May 2019 11:22:52 GMT

Hi,

Unfortunately, 400kbps seem to be about the maximum possible with iOS (https://devzone.nordicsemi.com/support-private/support/218063). There is a talk about throughput in: https://developer.apple.com/videos/play/wwdc2017/712/ from 30-31 minutes and onwards.

I guess you have also seen the throughput examples in the Softdevice specification here: Bluetooth Low Energy data throughput.