pc-ble-driver 1.0 - maximum data throughput

[Mike]

Hello,

I try to achieve maximum data throughput using pc-ble-driver 1.0 and nRF51(with ble_connectivity) as BLE dongle.

First problem I encountered was the bug with setting ble_conn_bw_counts_t parameters in the sd_ble_enable() but thanks to Hung Bui it was resolved here.

Unfortunately, it is still not possible to achieve maximum data throughput (128 kbit/s). I am able to achieve only around 16,8 kbit/s - not enough for me. Of course I set minimum avaliable connection interval (7.5ms) and high bandwidth with sd_ble_opt_set(). For tests I use nRF51 device as peripheral which sends data in infinite loop and prints count of successfully sent bits. The test device seems to be working properly because it has no problem to achieve maximum data throughput with the Master Control Panel 3.10.

Here is some code:

ble_enable_params_t ble_enable_params;
ble_enable_params.gatts_enable_params.attr_tab_size    = BLE_GATTS_ATTR_TAB_SIZE_DEFAULT;
ble_enable_params.gatts_enable_params.service_changed  = false;
ble_enable_params.gap_enable_params.periph_conn_count  = 0;
ble_enable_params.gap_enable_params.central_conn_count = 1;
ble_enable_params.gap_enable_params.central_sec_count  = 0;
ble_enable_params.common_enable_params.vs_uuid_count   = 3;


ble_conn_bw_counts_t ble_conn_bw_counts;
ble_conn_bw_counts.tx_counts.high_count     = 1;
ble_conn_bw_counts.tx_counts.mid_count      = 0;
ble_conn_bw_counts.tx_counts.low_count      = 0;
ble_conn_bw_counts.rx_counts.high_count     = 1;
ble_conn_bw_counts.rx_counts.mid_count      = 0;
ble_conn_bw_counts.rx_counts.low_count      = 0;
ble_enable_params.common_enable_params.p_conn_bw_counts = &ble_conn_bw_counts;


err_code = sd_ble_enable(adapter, &ble_enable_params, NULL);

_

ble_opt_t ble_opt;
ble_opt.common_opt.conn_bw.role = BLE_GAP_ROLE_CENTRAL;
ble_opt.common_opt.conn_bw.conn_bw.conn_bw_rx = BLE_CONN_BW_HIGH;
ble_opt.common_opt.conn_bw.conn_bw.conn_bw_tx = BLE_CONN_BW_HIGH;

uint32_t err_code = sd_ble_opt_set(adapter, BLE_COMMON_OPT_CONN_BW, &ble_opt);
...

I noticed that my peripheral device in not able to send me 6 packet per every connection interval. Sometimes it sends only 3 or 1 packet.

Could you tell me if it is possible to achieve maximum data throughput with ble_connectivity and pc-ble-driver? If yes, what I have to do?

EDIT: I've attached log form nRF Sniffer: SNIFF_LOG

[bjorn-spockeli]

Hi Mike,

I spoke to one of the pc-ble-driver developers and it appears that you have reached the throughput( ~16kbit/s) possible using the nRF5x DKs and dongles.

This is due to delays introduced by passing all the data through the Segger chip and that there are handshakes which further restricts the max communication speed.

Best regards

Bjørn

[Mike]

Hi Bjørn,

thank you for the answer but I do not use a development kit. My central device is the nRF51 chip connected directly to a second processor via UART.

I do not think that the Segger chip is a bottleneck because I've also made some tests with the same peripheral device and Master Control Panel with PCA10000 (which has a Segger chip) as a central. There was no problem with data throughput...

Best regards

Mike

EDIT: Maybe the UART speed is a problem. I use default 115200 baudrate... I will try to investigate it.