Service not discovered in BLE_Client example

[SensorsIot]

I use the BLE_notify example without changes and try to connect to it using the BLE_Client example. The only changes I did there was to copy the two UUID strings of the notify example to the client example to be sure they match.
NRF connect shows the service but BLE_Client does not show it and also does not connect.
Output: BLE Advertised Device found: Name: MyESP32, Address: 24:0a:c4:12:ef:a2, txPower: -21
I had this issue with many other examples but I am pretty sure it worked last week.
To be sure I also downloaded the newest ESP32 environment from GitHub, with no change
I also have a Xiaomi Flower care device around:
Output: BLE Advertised Device found: Name: Flower care, Address: c4:7c:8d:62:87:f7, serviceUUID: 0000fe95-0000-1000-8000-00805f9b34fb
If I copy this UUID to the client sketch, it connects.

[chegewara]

Hi,
one question, are you using library from https://github.com/nkolban/ESP32_BLE_Arduino or from https://github.com/nkolban/esp32-snippets. In other words, in arduino ide are installing library from zip file or from library manager?

[SensorsIot]

From the original distribution (with git clone)

[chegewara]

Original distribution is https://github.com/nkolban/esp32-snippets

[SensorsIot]

So there are differences between espressif/arduino-esp32 and https://github.com/nkolban/esp32-snippets? Which one do you suggest?

[chegewara]

At the moment, until we dont get support c++ exceptions in arduino-esp32 i suggest to not change to esp32-snippets, and when we have c++ exceptions working in arduino-ide most likely library delivered with arduino-esp32, which you call original distribution, will be updated.

Back to your issue, i will investigate it and back to you soon. In mean time, can you turn on verbose logging in arduino-ide and provide more logs?

[SensorsIot]

I switched it on and compiled the client file. Where should I post the log?

[chegewara]

pastebin or here

[SensorsIot]

It is here:
https://pastebin.com/5299TxCV

[chegewara]

Ok, ive found the problem. Those two examples are not prepared to work with each other without some changes. As you can see in this line https://github.com/nkolban/ESP32_BLE_Arduino/blob/f8fe9d7cdfb20caa54b70849826d1ac6e375ff78/examples/BLE_client/BLE_client.ino#L78
BLE_client expecting that server is advertising UUID, but BLE_notify example is not advertising any UUID. You can change it very easy by adding this line
pServer->getAdvertising()->addServiceUUID(BLEUUID(SERVICE_UUID)); somwhere in here https://github.com/nkolban/ESP32_BLE_Arduino/blob/f8fe9d7cdfb20caa54b70849826d1ac6e375ff78/examples/BLE_notify/BLE_notify.ino#L78
tis will let you to connect 2 esp32 by using BLE_client and BLE_notify examples. There is one more thing you have to remember. When you are advertising 128 bit UUID then name of device cant be longer than 5 characters.

[chegewara]

You can also change this line https://github.com/nkolban/ESP32_BLE_Arduino/blob/f8fe9d7cdfb20caa54b70849826d1ac6e375ff78/examples/BLE_client/BLE_client.ino#L78 and search device you want to connect to not by advertised UUID but ie by name, or served service etc

[SensorsIot]

Now it works. Very good! Thank you very much for your help. Now I can go on with my Polar H7 emulation... And with my new video where I need BLE UART functionality. So it is well possible that I have to come back because for the moment I can only transfer a few characters to my Smartphone...
Just a small question concerning your additional line: Why do I have to use BLEUUID(SERVICE_UUID) and not only (SERVICE_UUID)?

[chegewara]

You can use both, BLEUUID(SERVICE_UUID) and (SERVICE_UUID) because this method is overloaded and can be used with BLEUUID or with string uuid.

EDIT you can use both only in case if SERVICE_UUID is 128 bit uuid in string variable. In case you want to use 16 or 32 bit uuid only BLEUUID(SERVICE_UUID) works

[SensorsIot]

I try now to read the values sent by notify.
in BLE_notify I inserted:
cscCharacteristic.setValue(csc, 11);
cscCharacteristic.notify();

In BLE_client I am able to see the values once during connect of the characteristics:
in connectToServer(BLEAddress pAddress) at the bottom I inserted:
// Read the value of the characteristic.
std::string value = pRemoteCharacteristic->readValue();
Serial.println("The characteristic value was: ");
for (int i = 0; i < value.length(); i++) Serial.println(value[i], HEX);
Serial.print("length: ");
Serial.println(value.length());

But not during notifyCallback:

static void notifyCallback(
BLERemoteCharacteristic* pBLERemoteCharacteristic,
uint8_t* pData,
size_t length,
bool isNotify) {
Serial.print("Notify callback for characteristic ");
Serial.println(pBLERemoteCharacteristic->getUUID().toString().c_str());

Serial.println("The characteristic value was: ");
// Read the value of the characteristic.
std::string value = pBLERemoteCharacteristic->readValue();
for (int i = 0; i < value.length(); i++) Serial.println(value[i], HEX);
Serial.print("length: ");
Serial.println(value.length());
}
The callback is called, but the line std::string value = pBLERemoteCharacteristic->readValue(); blocks the execution
In NRFconnect the csc value counts up

The whole code is here (strongly based on the notify example)
https://pastebin.com/PbtSvvVU

And the notifier: https://pastebin.com/0ngKNkef (based on the Cadence and speed service)

[chegewara]

In my case with original BLE_notify and BLE_client i can receive notifications, but i will investigate custom code.

[chegewara]

I see the problem. Here you have created chracteristic with notify:
BLECharacteristic cscCharacteristic(BLEUUID((uint16_t)0x2A5B), BLECharacteristic::PROPERTY_READ | BLECharacteristic::PROPERTY_NOTIFY); thats good, but if you will check with nRF connect there is missing something. With properly implemented notify/indicate functionality you will see three arrows like on this picture http://a2.mzstatic.com/us/r30/Purple18/v4/21/65/4d/21654db0-6c4e-2237-18a5-624b22e783da/screen696x696.jpeg

This leads us to conclusion there is missing something. Every characteristic with notify and/or indicate needs to have descriptor 2902. There is special library which help to create and add this descriptor BLE2902.

[SensorsIot]

Thank you for your help. Sorry for coming back late. I was away. Now my H7 fake works and delivers values to nRF connect. I can switch notifications on and off using BLE2902. Great. I again watched Neils videos and understood them now much more. The next problem I have is on the client side and unfortunately, Neil did not explain in his client video is how to display the notified values in the client. I get them once the client connects to the server and, if I put a pRemoteCharacteristic->readValue(); in the loop() I get also the updates. But not in a callback, which would be much nicer to avoid getting the same value twice...
Also, I do not know how I can disable notifications from my ESP client (with the phone I just push the three arrows and the BLE2902 disables notifications).
Is there a documentation of these commands? I looked into Neils ESP32 book but it is somehow a mixture between c and c++

[chegewara]

No rush, we dont have timeline when you have to comeback and response.

Thats strange, you should have get notifications and read value in notificationCallback. See this code:
https://github.com/nkolban/esp32-snippets/blob/master/cpp_utils/tests/BLETests/Arduino/BLE_client/BLE_client.ino#L18

If you asking about turning on/off notifications, you need to read remoteDescriptor BLE2902 descriptor from pRemoteCharacteristic and then writeValue(bool):
https://github.com/nkolban/esp32-snippets/blob/master/cpp_utils/BLERemoteDescriptor.h#L36

pRemoteCharacteristic->getDescriptor(BLEUUID((uint16_t)0x2902)->writeValue(0)  <- TURN OFF
pRemoteCharacteristic->getDescriptor(BLEUUID((uint16_t)0x2902)->writeValue(1)  <- TURN ON NOTIFICATIONS ONLY
pRemoteCharacteristic->getDescriptor(BLEUUID((uint16_t)0x2902)->writeValue(2)  <- TURN ON INDICATIONS ONLY
pRemoteCharacteristic->getDescriptor(BLEUUID((uint16_t)0x2902)->writeValue(3)  <- TURN ON NOTIFICATIONS AND INDICATIONS

[SensorsIot]

Interesting things happen:

1. You are right. If I use Neils original script it triggers the notification callback. As soon as I try to read the value (std::string value = pBLERemoteCharacteristic->readValue();) it blocks in the callback function at the first call.
2. I tried to switch the notification on and off in loop :
   if (onoff) pRemoteCharacteristic->getDescriptor(BLEUUID((uint16_t)0x2902))->writeValue(0);
   else pRemoteCharacteristic->getDescriptor(BLEUUID((uint16_t)0x2902))->writeValue(1);
   If I look at Serial of the server, I get this message:
   E (2597062) BT: gatts_write_attr_perm_check - GATT_INVALID_PDU
   and the notifications do not stop.

[SensorsIot]

Sorry for #1. I was stupid and did not understand the concept. Now it works.
#2 still open...

[chegewara]

Nothing wrong happened, im glad it works.

[chegewara]

Sorry it takes so long, but honestly documentation on bluetooth.org sucks. This is the right solution to turn on notifications:

const uint8_t v[]={0x1,0x0};
pRemoteCharacteristic->getDescriptor(BLEUUID((uint16_t)0x2902))->writeValue((uint8_t*)v,2,false);

Explanation:

• you need to send 2 bytes
• value to send is 1 in bug endian order

If something else requires explanation dont hesitate to ask.

[SensorsIot]

I tried now your code and get the following response in the Server:
E (516057) BT: GATTS_SendRsp conn_id: 3 waiting for op_code = 00
E (516057) BT: Sending response failed
E (517077) BT: GATTS_SendRsp conn_id: 3 waiting for op_code = 00
E (517077) BT: Sending response failed
The notifications do not stop

I put the statement in the loop after (connectToServer(*pServerAddress). If I put it at the end of init the esp crashes. Is there a particular place where it has to go?
BTW what would then be the command to switch it on?

[chegewara]

For comparision i will post my code. This is client code, which will switch on/off notifications:

/**
 * A BLE client example that is rich in capabilities.
 */

#include "BLEDevice.h"
//#include "BLEScan.h"

// The remote service we wish to connect to.
static BLEUUID serviceUUID("4fafc201-1fb5-459e-8fcc-c5c9c331914b");
// The characteristic of the remote service we are interested in.
static BLEUUID    charUUID("beb5483e-36e1-4688-b7f5-ea07361b26a8");

static BLEAddress *pServerAddress;
static boolean doConnect = false;
static boolean connected = false;
static BLERemoteCharacteristic* pRemoteCharacteristic;

static void notifyCallback(
  BLERemoteCharacteristic* pBLERemoteCharacteristic,
  uint8_t* pData,
  size_t length,
  bool isNotify) {
    Serial.print("Notify callback for characteristic ");
    Serial.print(pBLERemoteCharacteristic->getUUID().toString().c_str());
    Serial.print(" of data length ");
    Serial.println(length);
}

bool connectToServer(BLEAddress pAddress) {
    Serial.print("Forming a connection to ");
    Serial.println(pAddress.toString().c_str());
    
    BLEClient*  pClient  = BLEDevice::createClient();
    Serial.println(" - Created client");

    // Connect to the remove BLE Server.
    pClient->connect(pAddress);
    Serial.println(" - Connected to server");

    // Obtain a reference to the service we are after in the remote BLE server.
    BLERemoteService* pRemoteService = pClient->getService(serviceUUID);
    if (pRemoteService == nullptr) {
      Serial.print("Failed to find our service UUID: ");
      Serial.println(serviceUUID.toString().c_str());
      return false;
    }
    Serial.println(" - Found our service");


    // Obtain a reference to the characteristic in the service of the remote BLE server.
    pRemoteCharacteristic = pRemoteService->getCharacteristic(charUUID);
    if (pRemoteCharacteristic == nullptr) {
      Serial.print("Failed to find our characteristic UUID: ");
      Serial.println(charUUID.toString().c_str());
      return false;
    }
    Serial.println(" - Found our characteristic");

    // Read the value of the characteristic.
    std::string value = pRemoteCharacteristic->readValue();
    Serial.print("The characteristic value was: ");
    Serial.println(value.c_str());

    pRemoteCharacteristic->registerForNotify(notifyCallback);
delay(100);
}
/**
 * Scan for BLE servers and find the first one that advertises the service we are looking for.
 */
class MyAdvertisedDeviceCallbacks: public BLEAdvertisedDeviceCallbacks {
 /**
   * Called for each advertising BLE server.
   */
  void onResult(BLEAdvertisedDevice advertisedDevice) {
    Serial.print("BLE Advertised Device found: ");
    Serial.println(advertisedDevice.toString().c_str());

    // We have found a device, let us now see if it contains the service we are looking for.
    if (1) {  <-- THIS is not important in my case, i have just 1 device so i want to connect to first found device, but in normal case its required to search device by name, or advertised service or any other parameter

      // 
      Serial.print("Found our device!  address: "); 
      advertisedDevice.getScan()->stop();

      pServerAddress = new BLEAddress(advertisedDevice.getAddress());
      doConnect = true;

    } // Found our server
  } // onResult
}; // MyAdvertisedDeviceCallbacks


void setup() {
  Serial.begin(115200);
  Serial.println("Starting Arduino BLE Client application...");
  BLEDevice::init("");

  // Retrieve a Scanner and set the callback we want to use to be informed when we
  // have detected a new device.  Specify that we want active scanning and start the
  // scan to run for 30 seconds.
  BLEScan* pBLEScan = BLEDevice::getScan();
  pBLEScan->setAdvertisedDeviceCallbacks(new MyAdvertisedDeviceCallbacks());
  pBLEScan->setActiveScan(true);
  pBLEScan->start(1);
} // End of setup.


// This is the Arduino main loop function.
bool onoff = false;

const uint8_t x[]={0x0,0x0};
const uint8_t v[]={0x1,0x0};
void loop() {

  // If the flag "doConnect" is true then we have scanned for and found the desired
  // BLE Server with which we wish to connect.  Now we connect to it.  Once we are 
  // connected we set the connected flag to be true.
  if (doConnect == true) {
    if (connectToServer(*pServerAddress)) {
      Serial.println("We are now connected to the BLE Server.");
      connected = true;
    } else {
      Serial.println("We have failed to connect to the server; there is nothin more we will do.");
    }
    doConnect = false;
  }

  // If we are connected to a peer BLE Server, update the characteristic each time we are reached
  // with the current time since boot.
  if (connected) {
    String newValue = "Time since boot: " + String(millis()/1000);
    Serial.println("Setting new characteristic value to \"" + newValue + "\"");
    
    // Set the characteristic's value to be the array of bytes that is actually a string.
    pRemoteCharacteristic->writeValue(newValue.c_str(), newValue.length());
    if (onoff) pRemoteCharacteristic->getDescriptor(BLEUUID((uint16_t)0x2902))->writeValue((uint8_t*)x, 2, true);
    else     pRemoteCharacteristic->getDescriptor(BLEUUID((uint16_t)0x2902))->writeValue((uint8_t*)v,2,true);

onoff=onoff?0:1;
  }
  
  delay(10000); // Delay a second between loops.
} // End of loop

Server code is BLE_notify

[SensorsIot]

Great! Now it works here too. I still get these messages from the server.

E (311726) BT: GATTS_SendRsp conn_id: 3 waiting for op_code = 00
E (311726) BT: Sending response failed

But who cares if it works ;-)
Thank you for your help. I learned a lot in the last two days.
BTW: I was able to transfer messages with a length of 140 bytes. This is important for my next project. It seems, that this BLE is really cool stuff.

[chegewara]

Yes, im getting those messages too. But they are from esp-idf stack and sometimes even if they are suggesting its error (E) it is for information purpose only.

PS thanks to you i learned some stuff too, especially about descriptors and switching remote notifications.

[SensorsIot]

Thanks. They do not appear if I switch notification off from nRF. So it seems to be a difference between the ESP sketch and the nRF. Minor thing...

[kurtbeheydt]

@chegewara I have the same problem in the BLE_uart.ino demo.
I added as you suggested the extra line (line 100):
pServer->getAdvertising()->addServiceUUID(BLEUUID(SERVICE_UUID));

But the serviceUUID seems not advertised as it should be (see screenshot):

I am using version 0.4.13 of the library:

When I connect manually, the UART service becomes available, but I can't scan on devices advertising this serviceUUID.

Is there anything I can do?

[chegewara]

There is 2 options:

• short UART device name to 5 characters or less,
• or, which ive found just few days ago, dont advertise name like we always do but add it to scan advertising.

[kurtbeheydt]

Thx. the first trick did the job!
But I don't quite understand what you mean bij adding it to the scan advertising?

for the moment the advertising part are these lines:

  // Start the service
  pService->start();

  // Start advertising
  pServer->getAdvertising()->addServiceUUID(BLEUUID(SERVICE_UUID));
  pServer->getAdvertising()->start();

[chegewara]

Yes, but you have regular advertising packet and scan advertising packet, 31 bytes each.

[kurtbeheydt]

Can you explain that to me with an example?

[chegewara]

You can set two different set of advertising data:
https://github.com/nkolban/esp32-snippets/blob/master/cpp_utils/BLEAdvertising.cpp#L139-L166

[kurtbeheydt]

I am trying to understand it, but this does not seem te work with a devicename > 5 characters:

  // Start the service
  pService->start();

  // Start advertising
  BLEAdvertising *pAdvertising;
  pAdvertising = pServer->getAdvertising();
  pAdvertising->addServiceUUID(BLEUUID(SERVICE_UUID));
  BLEAdvertisementData oScanResponseData = BLEAdvertisementData();
  pAdvertising->setScanResponseData(oScanResponseData);
  pAdvertising->start();

[chegewara]

You need to leave with empty name BLEDevice::init("") and set it here for scan response (oScanResponseData ):
https://github.com/nkolban/esp32-snippets/blob/master/cpp_utils/BLEAdvertising.h#L28

[kurtbeheydt]

// Start advertising
  BLEAdvertising *pAdvertising;
  pAdvertising = pServer->getAdvertising();
  pAdvertising->addServiceUUID(BLEUUID(SERVICE_UUID));
  BLEAdvertisementData oScanResponseData = BLEAdvertisementData();
  oScanResponseData->setName("myUartDevice");
  pAdvertising->setScanResponseData(oScanResponseData);
  pAdvertising->start();

gives an error now: base operand of '->' has non-pointer type 'BLEAdvertisementData' but in the documentation it should be?

BLE is driving me crazy ;)

[bretmh]

I'm not working with Arduino, but with a mobile framework. When writing data I was also receiving the error E (982295) BT_GATT: GATTS_SendRsp conn_id: 3 waiting for op_code = 00

Upon writing to a characteristic, there are typically two options. WriteWithoutResponse or WriteWithRepsonse, make sure to WriteWithResponse to avoid any response errors on ESP.