Hello,
I would like to prepare BLE app with service responsible for sendind data from sensor. Needed throughput is ~250kbit/s. Based on ble_app_uart I made service which is sending notifications (each notification = 240B of sensor data).
Setup:
- nRF SDK v17.1.0
- nRF SoftDevice S140 7.2.0
- Sample program used: ble_app_hrs_freertos + "ble_app_uart"
(FreeRTOS model from (ble_app_hrs_freertos) and ble service base from ble_app_uart)
- PHY 1M
#define MIN_CONN_INTERVAL 6 /* 7,5ms */ #define MAX_CONN_INTERVAL MSEC_TO_UNITS(30, UNIT_1_25_MS) #define NRF_SDH_BLE_GAP_DATA_LENGTH 251 #define NRF_SDH_BLE_GATT_MAX_MTU_SIZE 247 #define NRF_SDH_BLE_GAP_EVENT_LENGTH 24 #define BLE_GATTS_HVN_TX_QUEUE_SIZE 30
Inside ble_stack_init() I added this to increase amount of buffers:
/* Configure number of TX notifications buffers */ ble_cfg_t bleCfg; memset(&bleCfg, 0, sizeof(bleCfg)); bleCfg.conn_cfg.conn_cfg_tag = APP_BLE_CONN_CFG_TAG; bleCfg.conn_cfg.params.gatts_conn_cfg.hvn_tx_queue_size = BLE_GATTS_HVN_TX_QUEUE_SIZE; errCode = sd_ble_cfg_set(BLE_CONN_CFG_GATTS, &bleCfg, ramStart); APP_ERROR_CHECK(errCode); bleNotificationsAvailable = (int8_t)BLE_GATTS_HVN_TX_QUEUE_SIZE;
I added conn_evt_len_ext_set() and call it after ble_stack_init()
void conn_evt_len_ext_set()
{
ret_code_t err_code;
ble_opt_t opt;
memset(&opt, 0x00, sizeof(opt));
opt.common_opt.conn_evt_ext.enable = 1;
err_code = sd_ble_opt_set(BLE_COMMON_OPT_CONN_EVT_EXT, &opt);
APP_ERROR_CHECK(err_code);
}
To verify my code I am working with nRF Connect 3.7.0 and Bluetooth Low Energy tool.
On nrfDongle (Client) connection interval is set to 30ms.
I am testing some cases and my observations are:
1. When I try to send notification (call sd_ble_gatts_hvx) slower than connestion inverval (e.g. 35ms) app works.
2. When I try to send notification (call sd_ble_gatts_hvx) little bit faster than connection interval (e.g. 25ms) it still works. I observe how number of free Tx buffers is changing between 27-30. Observing this changes is possible by adding counter wich is decremented after sd_ble_gatts_hvx() and incremented when event BLE_GATTS_EVT_HVN_TX_COMPLETE occurs. So in this case app it works as expected.
3. When I try to send notification (call sd_ble_gatts_hvx) faster than connection interval (e.g. 20ms) after few seconds of operation there is no free TX buffers and sd_ble_gatts_hvx returns NRF_ERROR_RESOURCES.
It looks like Soft Device is too slow. I have made some time measurements and time between calling sd_ble_gatts_hvx() and the occurrence of BLE_GATTS_EVT_HVN_TX_COMPLETE is between few to more than 20ms.
I suppose there is problem with my settings.
What should I do send multiple packets at every connection interval?
Do you see any issues with my code?
