How to discover vendor service

[Yuta]

Hi,

I want to develop central code to discover vender specific service using pc-ble-driver-py.

The service_discovery function defined in ble_adapter.py can discover the vender service, but cannot collect it.
Because, the following guard conditions on Line: 326 prevent collection.

The following is an excerpt of the service_discovery function defined in ble_adapter.py. (line: 322-329)

322:            if response["status"] == BLEGattStatusCode.success:
323:                # Assign UUIDBase manually
324:                # See:
325:                #  https://github.com/NordicSemiconductor/pc-ble-driver-py/issues/38
326:                for s in response["services"]:
327:                    if s.uuid.value != BLEUUID.Standard.unknown:
328:                        s.uuid.base = base
329:                        self.db_conns[conn_handle].services.append(s)

What is the intent of this guard condition?
I have confirmed that the vender service can be collected by deleting the guard condition in line 326.

[Vidar Berg]

Hi,

To discover vendor specific services you need add the UUIDBase manually as noted in the comment. Attached below is an example I have made to discover the 128-bit Nordic UART service which you can use as a reference.

Fullscreen nus_central.py Download

#
# Copyright (c) 2016 Nordic Semiconductor ASA
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# are permitted provided that the following conditions are met:
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#   contributors to this software may be used to endorse or promote products
#   derived from this software without specific prior written permission.
#
#   4. This software must only be used in or with a processor manufactured by Nordic
#   Semiconductor ASA, or in or with a processor manufactured by a third party that
#   is used in combination with a processor manufactured by Nordic Semiconductor.
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# ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
# (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
# SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
#

import sys
import time
import logging
from queue import Queue, Empty
from pc_ble_driver_py.observers import *

TARGET_DEV_NAME = "Nordic_UART"
CONNECTIONS = 1
CFG_TAG = 1


def init(conn_ic_id):
    # noinspection PyGlobalUndefined
    global config, BLEDriver, BLEAdvData, BLEEvtID, BLEAdapter, BLEEnableParams, BLEGapTimeoutSrc, BLEUUID, BLEUUIDBase, BLEConfigCommon, BLEConfig, BLEConfigConnGatt, BLEGapScanParams
    from pc_ble_driver_py import config

    config.__conn_ic_id__ = conn_ic_id
    # noinspection PyUnresolvedReferences
    from pc_ble_driver_py.ble_driver import (
        BLEDriver,
        BLEAdvData,
        BLEEvtID,
        BLEEnableParams,
        BLEGapTimeoutSrc,
        BLEUUID,
        BLEUUIDBase,
        BLEGapScanParams,
        BLEConfigCommon,
        BLEConfig,
        BLEConfigConnGatt,
    )

    # noinspection PyUnresolvedReferences
    from pc_ble_driver_py.ble_adapter import BLEAdapter

    global nrf_sd_ble_api_ver
    nrf_sd_ble_api_ver = config.sd_api_ver_get()


class NusCollector(BLEDriverObserver, BLEAdapterObserver):
    def __init__(self, adapter):
        super(NusCollector, self).__init__()
        self.first = 1
        self.adapter = adapter
        self.conn_q = Queue()
        self.adapter.observer_register(self)
        self.adapter.driver.observer_register(self)
        self.adapter.default_mtu = 300
        self.nus_base = BLEUUIDBase([
            0x6e, 0x40, 0x00, 0x00, 0xb5, 0xa3, 0xf3, 0x93, 0xe0, 0xa9, 0xe5, 0x0e, 0x24, 0xdc, 0xca, 0x9e
        ])
        self.nus_rx = BLEUUID(0x0002, self.nus_base)
        self.nus_tx = BLEUUID(0x0003, self.nus_base)

    def open(self):
        self.adapter.driver.open()
        if config.__conn_ic_id__ == "NRF51":
            self.adapter.driver.ble_enable(
                BLEEnableParams(
                    vs_uuid_count=1,
                    service_changed=0,
                    periph_conn_count=0,
                    central_conn_count=1,
                    central_sec_count=0,
                )
            )
        elif config.__conn_ic_id__ == "NRF52":
            gatt_cfg = BLEConfigConnGatt()
            gatt_cfg.att_mtu = self.adapter.default_mtu
            gatt_cfg.tag = CFG_TAG
            self.adapter.driver.ble_cfg_set(BLEConfig.conn_gatt, gatt_cfg)

            self.adapter.driver.ble_enable()
            self.adapter.driver.ble_vs_uuid_add(self.nus_base)



    def close(self):
        self.adapter.driver.close()

    def connect_and_discover(self):
        scan_duration = 5
        params = BLEGapScanParams(interval_ms=200, window_ms=150, timeout_s=scan_duration)
        message = "We are connected!\r\n"

        self.adapter.driver.ble_gap_scan_start(scan_params=params)

        try:
            new_conn = self.conn_q.get(timeout=scan_duration)
            self.adapter.service_discovery(new_conn)
            self.adapter.enable_notification(new_conn, self.nus_tx)
            #data = [ord(n) for n in list(message)]
            data = [49]*244
            print(data)
            print(type(data))
            self.adapter.write_cmd(new_conn, self.nus_rx, data)
            return new_conn
        except Empty:
            print("No device advertising with name {TARGET_DEV_NAME} found.")
            return None

    def on_gattc_evt_exchange_mtu_rsp(self, ble_driver, conn_handle, status, att_mtu):
        print("ATT MTU updated to {}".format(att_mtu))
    
    def on_gap_evt_data_length_update(
        self, ble_driver, conn_handle, data_length_params
    ):
        print("Max rx octets: {}".format(data_length_params.max_rx_octets))
        print("Max tx octets: {}".format(data_length_params.max_tx_octets))
        print("Max rx time: {}".format(data_length_params.max_rx_time_us))
        print("Max tx time: {}".format(data_length_params.max_tx_time_us))

    def on_gatts_evt_exchange_mtu_request(self, ble_driver, conn_handle, client_mtu):
        print("Client requesting to update ATT MTU to {} bytes".format(client_mtu))
    def on_gap_evt_connected(
        self, ble_driver, conn_handle, peer_addr, role, conn_params
    ):
        print("New connection: {}".format(conn_handle))
        self.conn_q.put(conn_handle)

    def on_gap_evt_disconnected(self, ble_driver, conn_handle, reason):
        print("Disconnected: {} {}".format(conn_handle, reason))

    def on_gap_evt_adv_report(
        self, ble_driver, conn_handle, peer_addr, rssi, adv_type, adv_data
    ):
        if BLEAdvData.Types.complete_local_name in adv_data.records:
            dev_name_list = adv_data.records[BLEAdvData.Types.complete_local_name]

        elif BLEAdvData.Types.short_local_name in adv_data.records:
            dev_name_list = adv_data.records[BLEAdvData.Types.short_local_name]

        else:
            return

        dev_name = "".join(chr(e) for e in dev_name_list)
        address_string = "".join("{0:02X}".format(b) for b in peer_addr.addr)
        print(
            "Received advertisment report, address: 0x{}, device_name: {}".format(
                address_string, dev_name
            )
        )

        if dev_name == TARGET_DEV_NAME:
            self.adapter.connect(peer_addr, tag=CFG_TAG)

    def on_notification(self, ble_adapter, conn_handle, uuid, data):
        if len(data) > 32:
            data = "({}...)".format(data[0:10])
        print("Connection: {}, {} = {}".format(conn_handle, uuid, data))


def main(selected_serial_port):
    print("Serial port used: {}".format(selected_serial_port))
    driver = BLEDriver(
        serial_port=selected_serial_port, auto_flash=False, baud_rate=1000000, log_severity_level="info"
    )

    adapter = BLEAdapter(driver)
    collector = NusCollector(adapter)
    collector.open()
    conn = collector.connect_and_discover()

    while conn is not None:
        time.sleep(100)

    collector.close()


def item_choose(item_list):
    for i, it in enumerate(item_list):
        print("\t{} : {}".format(i, it))
    print(" ")

    while True:
        try:
            choice = int(input("Enter your choice: "))
            if (choice >= 0) and (choice < len(item_list)):
                break
        except Exception:
            pass
        print("\tTry again...")
    return choice


if __name__ == "__main__":
    logging.basicConfig(
        level="DEBUG",
        format="%(asctime)s [%(thread)d/%(threadName)s] %(message)s",
    )
    serial_port = None
    if len(sys.argv) < 2:
        print("Please specify connectivity IC identifier (NRF51, NRF52)")
        exit(1)
    init(sys.argv[1])
    if len(sys.argv) == 3:
        serial_port = sys.argv[2]
    else:
        descs = BLEDriver.enum_serial_ports()
        choices = ["{}: {}".format(d.port, d.serial_number) for d in descs]
        choice = item_choose(choices)
        serial_port = descs[choice].port
    main(serial_port)
    quit()

Best regards,

Vidar

[Yuta]

Hi,

Thank you for your quick reply

But the result was the same. It can be detected, but it is not collected in self.db_conns.

The Base UUID of our vender service is the following value.

00000000-XXXX-XXXX-XXXX-XXXXXXXXXXXX

In other words, the part corresponding to 16bit UUID matches 0x0000 = BLEUUID.Standard.unknown.
Therefore, the guard on line 327 will prevent collection.

In our use case, we would like to remove the guard statement.
However, we are worried about side effects, because we do not understand the intent of this guard statement.

Best regards,

Yuta

[Vidar Berg]

Hi,

Yes, it looks like the correct fix is to remove the guard as you said. Please see discussion in this pull request for details: https://github.com/NordicSemiconductor/pc-ble-driver-py/pull/167 

Best regards,

Vidar

[Yuta]

HI,

Thank you for introducing the pull request.
I understand the intent of this code and the side effects of removing the guard statement.

Best regards,

Yuta