RE: Unable to receive notifications from peripheral after reconnect

alcalaj — Thu, 29 Aug 2019 15:55:38 GMT

Hello again everyone,

After looking through the code thoroughly, I figured out that the error was actually in my added code and not the in the ble nus code. The central was able to connect, disconnect and reconnect correctly. The error was that when I send the data string to the peripheral, I calculate a checksum using a temporary variable which should then get cleared after the checksum is sent. My mistake was that I was not clearing the temporary value and therefore, an incorrect checksum was being sent to the peripheral after a reconnect.

Sorry for taking up some of your time on an error that was completely my fault and not a ble issue. But also thank you for taking time to look at my question.

RE: Unable to receive notifications from peripheral after reconnect

alcalaj — Thu, 29 Aug 2019 14:27:50 GMT

Thanks for the reply!

Yes, I am using the ble_nus_data_send() and ble_nus_c_data_send().

I used the SEGGER_RTT_printf() function to print out the ble events that occur in my program:

When notifications don't show up on the device I get event BLE_GATTC_EVT_WRITE_CMD_TX_COMPLETE

and then the program waits for the next event which never comes.

When I do get notifications on the first connection, I get the event:

BLE_GATTC_EVT_WRITE_CMD_TX_COMPLETE

followed by the event:

BLE_GATTC_EVT_HVX

which then triggers the UART print events.

I don't know if this will help but here is the complete list of ble events that occur from the first connection and correct transfer of data until the second connection when the data transfer fails.

I used SEGGER_RTT_printf() in the function nrf_sdh_ble_evts_poll() to print the ble events as they occur. I have listed the event id and enumeration name. I have also added notes that hopefully make the work flow clear:

DEBUG STARTS

BLE event: 0x1D. BLE_GAP_EVT_ADV_REPORT              <== Scanning
BLE event: 0x10. BLE_GAP_EVT_CONNECTED               <== Peripheral is found

BLE event: 0x24.   BLE_GAP_EVT_DATA_LENGTH_UPDATE
BLE event: 0x3A.   BLE_GATTC_EVT_EXCHANGE_MTU_RSP

BLE event: 0x30. BLE_GATTC_EVT_PRIM_SRVC_DISC_RSP
BLE event: 0x32. BLE_GATTC_EVT_CHAR_DISC_RSP
BLE event: 0x32. BLE_GATTC_EVT_CHAR_DISC_RSP
BLE event: 0x33. BLE_GATTC_EVT_DESC_DISC_RSP
BLE event: 0x30. BLE_GATTC_EVT_PRIM_SRVC_DISC_RSP <== NUS service discovered

Connected to device with NUS Comm Service. <== Debug message I use to indicate connection

BLE event: 0x38. BLE_GATTC_EVT_WRITE_RSP <== cccd configured to enable notifications on peripheral

BLE event: 0x1F. BLE_GAP_EVT_CONN_PARAM_UPDATE_REQUEST
BLE event: 0x12. BLE_GAP_EVT_RSSI_CHANGED

Data hex: 0x54 68 69 73 20 69 73 20 61 20 6d 65 73 73 61 67 65 20 34 75    <== Random data string that I send
BLE event: 0x3C. BLE_GATTC_EVT_WRITE_CMD_TX_COMPLETE           <== data is sent
BLE event: 0x39. BLE_GATTC_EVT_HVX                                                   <== central receives a notification with reply string

Receiving data from KN                                                                            <== Name of our peripheral
Data hex: 0x54 68 69 73 20 69 73 20 61 20 72 65 70 6c 79 20 34 75     <== Reply string of random data

BLE event: 0x11. BLE_GAP_EVT_DISCONNECTED                             <== Peripheral disconnects

BLE event: 0x1D. BLE_GAP_EVT_ADV_REPORT      <== Scanning
BLE event: 0x10. BLE_GAP_EVT_CONNECTED        <== Peripheral is found again and connects for the second time

BLE event: 0x11. BLE_GAP_EVT_DISCONNECTED <== Peripheral disconnects (this doesn't always happen)

BLE event: 0x1D. BLE_GAP_EVT_ADV_REPORT    <== Scanning
BLE event: 0x10. BLE_GAP_EVT_CONNECTED      <== Peripheral is found again connects for the third time

BLE event: 0x24. BLE_GAP_EVT_DATA_LENGTH_UPDATE
BLE event: 0x3A. BLE_GATTC_EVT_EXCHANGE_MTU_RSP

BLE event: 0x30. BLE_GATTC_EVT_PRIM_SRVC_DISC_RSP
BLE event: 0x32. BLE_GATTC_EVT_CHAR_DISC_RSP
BLE event: 0x32. BLE_GATTC_EVT_CHAR_DISC_RSP
BLE event: 0x33. BLE_GATTC_EVT_DESC_DISC_RSP
BLE event: 0x30. BLE_GATTC_EVT_PRIM_SRVC_DISC_RSP <== NUS service discovered

Connected to device with NUS Comm Service. <== Debug message I use to indicate connection

BLE event: 0x38. BLE_GATTC_EVT_WRITE_RSP <== cccd configured to enable notifications on peripheral

BLE event: 0x1F. BLE_GAP_EVT_CONN_PARAM_UPDATE_REQUEST
BLE event: 0x12. BLE_GAP_EVT_RSSI_CHANGED

Data hex: 0x54 68 69 73 20 69 73 20 61 20 6d 65 73 73 61 67 65 20 34 75 <== Random data string that I send
BLE event: 0x3C. BLE_GATTC_EVT_WRITE_CMD_TX_COMPLETE <== data is sent

This is where the events stop occurring. On subsequent events, I don't receive BLE_GATTC_EVT_HVX events which makes me believe that notifications might not actually enabled on the peripheral.

RE: Unable to receive notifications from peripheral after reconnect

Edvin — Thu, 29 Aug 2019 12:03:13 GMT

Hello,

Enabling notifications is only necessary to be able to send notifications from peripheral to central, not the other way around.

I assume that you are using the functions ble_nus_data_send() and ble_nus_c_data_send() to send data between the devices, right?

Can you check what that call returns when the notifications doesn't show up on the other device?