Multilink central disconnect problem

RE: Multilink central disconnect problem

FormerMember — Tue, 20 Jun 2017 13:02:13 GMT

This chapter in the S132 softdevice specification explains the relationship between connection interval, event length, and number of links. I would recommend you to read that chapter.

RE: Multilink central disconnect problem

Rbai — Mon, 19 Jun 2017 22:33:52 GMT

Can you explain the relationship among number of links, my_connection_event_length, and connection interval? Eg. if I have 8 links in total, 100ms connection interval, what to set the my_connection_event_length?

RE: Multilink central disconnect problem

FormerMember — Mon, 19 Jun 2017 12:56:45 GMT

I have updated my answer with what is necessary to do to obtain stable connections.

RE: Multilink central disconnect problem

Rbai — Thu, 15 Jun 2017 16:14:25 GMT

Thought this issue was solved but not yet. Things are fine with MTU=23 and 3 peripherals. After I change the MTU size to 247 on both ends, the discovery became much slower than when MTU=23. The connection also became unstable, it would disconnect the 3rd peripheral always, and even the first two would disconnect sometimes. Can you verify and tell me how to solve it?

I have also added code as following for MTU=247 and called them with "true" in main():

static void conn_evt_len_ext_set(bool status) { ret_code_t err_code; ble_opt_t opt;

memset(&opt, 0x00, sizeof(opt));
opt.common_opt.conn_evt_ext.enable = status ? 1 : 0;

err_code = sd_ble_opt_set(BLE_COMMON_OPT_CONN_EVT_EXT, &opt);
APP_ERROR_CHECK(err_code);

NRF_LOG_DEBUG("Setting connection event length extension to %u: 0x%x\r\n", status, err_code);

}

static void data_len_ext_set(bool status) { uint8_t data_length = status ? (247 + LL_HEADER_LEN) : (23 + LL_HEADER_LEN); (void) nrf_ble_gatt_data_length_set(&m_gatt, BLE_CONN_HANDLE_INVALID, data_length); }

RE: Multilink central disconnect problem

FormerMember — Tue, 13 Jun 2017 12:16:23 GMT

The disconnect is because of this bug in the GATT module (nrf_ble_gatt.h/.c): nrf_ble_gatt.h locally sets and uses its own settings for the number of connections, which by default is '2'. Changing the defines in nrf_ble_gatt.h to the correct value, or redefining NRF_BLE_CENTRAL_LINK_COUNT/NRF_BLE_PERIPHERAL_LINK_COUNT should solve the problem.

Update 19.06.17: To make the links stable for longer packets, the following changes have to be made:

Increase the connection interval: It takes more time to transmit longer packets, and each connected peripheral will require some time.

Configure the softdevice with the correct GAP and GATT parameters in ble_stack_init(), both for the central and the peripherals:

 memset(&ble_cfg, 0, sizeof(ble_cfg));
 ble_cfg.conn_cfg.params.gap_conn_cfg.conn_count     = PERIPHERAL_LINK_COUNT + CENTRAL_LINK_COUNT;
 ble_cfg.conn_cfg.params.gap_conn_cfg.event_length   = my_connection_event_length; 
 ble_cfg.conn_cfg.conn_cfg_tag                       = CONN_CFG_TAG;

 err_code = sd_ble_cfg_set(BLE_CONN_CFG_GAP, &ble_cfg, ram_start);
 APP_ERROR_CHECK(err_code);

 memset(&ble_cfg, 0, sizeof(ble_cfg));
 ble_cfg.conn_cfg.params.gatt_conn_cfg.att_mtu       = NRF_BLE_GATT_MAX_MTU_SIZE;
 ble_cfg.conn_cfg.conn_cfg_tag                       = CONN_CFG_TAG;

 err_code = sd_ble_cfg_set(BLE_CONN_CFG_GATT, &ble_cfg, ram_start);
 APP_ERROR_CHECK(err_code);

RE: Multilink central disconnect problem

Rbai — Mon, 12 Jun 2017 15:00:06 GMT

The message is from the central. APP:INFO:LBS central link 0x2 disconnected (reason: 0x13) Yes it is under BLE_GAP_EVT_DISCONNECTED event.

If you build and download the ble_app_uart into 3 peripheral devices and modify the ble_app_multilink_central to match the device name: static char const m_target_periph_name[] = "Nordic_UART";//"Nordic_Blinky"; Build and download the SW into a central device, you will see 3 connections on the console of the central, and the disconnect on the 3rd device every 30 seconds.

RE: Multilink central disconnect problem

FormerMember — Mon, 12 Jun 2017 07:48:07 GMT

0x13, is that an error code returned by a softdevice function or a BLE disconnected event code (BLE_GAP_EVT_DISCONNECTED)? This error occurs at the central side, right?