Getting Unknown Error while writing data on BLE in iOS - ios

Question

I am trying to develop iOS app, which is detecting BLE device and need to invoke a write command. I can successfully connect to BLE device and discover its service and characteristics. But I am getting an Unknown Error during the write data on connected peripheral. Below is the code what I have written:
Discovered Characteristic:
- (void)peripheral:(CBPeripheral *)peripheral didDiscoverCharacteristicsForService:(CBService *)service error:(NSError *)error {
NSArray *characteristics = [service characteristics];
if (peripheral != self.peripheral) {
NSLog(#"Wrong Peripheral.\n");
return ;
}
if (error != nil) {
NSLog(#"Error %#\n", error);
return ;
}
for (CBCharacteristic *characteristic in characteristics) {
if ([[characteristic UUID] isEqual:RWT_POSITION_CHAR_UUID]) {
self.positionCharacteristic = characteristic;
}
}
}
Here is the function for write data on BLE device
- (void)writeCommand{
// See if characteristic has been discovered before writing to it
if (!self.positionCharacteristic) {
return;
}
NSString *cmd1=#"CQ+WHORU\r";
NSData *dataToWrite = [cmd1 dataUsingEncoding:NSUTF8StringEncoding];
CBCharacteristic *chr = self.positionCharacteristic;
NSLog(#"%#,%lu...%#",chr.UUID,chr.properties,chr);
NSInteger dataSize = [[NSByteCountFormatter stringFromByteCount:dataToWrite.length countStyle:NSByteCountFormatterCountStyleFile] integerValue];
if (dataSize > 130) {
NSLog(#"Cannot send more than 130 bytes");
}
else
{
[self.peripheral writeValue:dataToWrite forCharacteristic:self.positionCharacteristic type:CBCharacteristicWriteWithResponse];
}
}
- (void)peripheral:(CBPeripheral *)peripheral
didWriteValueForCharacteristic:(CBCharacteristic *)characteristic
error:(NSError *)error
{
if (error)
{
NSLog(#"Error writing characteristic value: %#", [error localizedDescription]);
}
else
{
NSLog(#"Successfully writing characteristic value");
}
}
In "didWriteValueForCharacteristic" delegate method I am getting below error:
Error writing characteristic value: Unknown error.
What could be possibly be the reason for this error?
Also If I am trying to define characteristic for sending data on BLE device like:
CBMutableCharacteristic *writeChar = [[CBMutableCharacteristic alloc]initWithType:[CBUUID UUIDWithString:#"ffe1"] properties:CBCharacteristicPropertyWriteWithoutResponse|CBCharacteristicPropertyNotify value:nil permissions:CBAttributePermissionsWriteable|CBAttributePermissionsReadable];
int8_t cmd = *[cmd1 UTF8String];
NSData *data = [NSData dataWithBytes:&cmd length:sizeof(cmd)];
NSInteger dataSize = [[NSByteCountFormatter stringFromByteCount:dataToWrite.length countStyle:NSByteCountFormatterCountStyleFile] integerValue];
if (dataSize > 130) {
NSLog(#"Cannot send more than 130 bytes");
}
else
{
[self.peripheral writeValue:dataToWrite forCharacteristic:writeChar type:CBCharacteristicWriteWithResponse];
// [self.peripheral writeValue:dataToWrite forCharacteristic:writeChar type:CBCharacteristicWriteWithResponse];
}
then I am getting this error:
**CoreBluetooth[WARNING] CBMutableCharacteristic: 0x1552a270 UUID = Unknown (<ffe1>),Value = (null), Properties = 0x14, Permissions = 0x3, Descriptors = (null), SubscribedCentrals = (
)> is not a valid characteristic for peripheral <CBPeripheral: 0x15549930 identifier = FC71890D-9F71-5E16-086D-D491E1EF7599, Name = " DEMOBLE1", state = connected**

Answer 1

When you write the data you're requesting a response (CBCharacteristicWriteWithResponse).
The write will fail if the characteristic you're writing to does not have the property CBCharacteristicPropertyWrite set, but only supports writes without response (CBCharacteristicPropertyWriteWithoutResponse).
if ((self.positionCharacteristic.properties & CBCharacteristicPropertyWrite) == CBCharacteristicPropertyWrite) {
// Responses are available, so write with response.
[self.peripheral writeValue:dataToWrite forCharacteristic:self.positionCharacteristic type:CBCharacteristicWriteWithResponse];
}
else if ((self.positionCharacteristic.properties & CBCharacteristicPropertyWriteWithoutResponse) == CBCharacteristicPropertyWriteWithoutResponse) {
// Responses are not available.
// Write with response is going to fail, so write without response.
[self.peripheral writeValue:dataToWrite forCharacteristic:self.positionCharacteristic type:CBCharacteristicWriteWithoutResponse];
}

Answer 2

I have seen this error while developing both the iOS App (as Central) and the BLE Device firmware (as Peripheral). This would occur when I changed/modified the characteristics on the BLE peripheral.
iOS seems to cache information about the services and characteristics after a connection. I was able to solve this by updating the Bluetooth Address of the peripheral whenever I would build/download new firmware to the Device.

Answer 3

First of all, you are using CBCentralManager, right?
Make sure you are doing it in the right way:
Use CBCentralManager
self.centralManager = [[CBCentralManager alloc] initWithDelegate:self queue:nil];
Detect when a peripheral connected
- (void)centralManager:(CBCentralManager *)central didConnectPeripheral:(CBPeripheral *)peripheral
{
if (connectedDevice) // make sure you disconnect previous device
[self.centralManager cancelPeripheralConnection:connectedDevice];
connectedDevice = [peripheral retain];
connectedDevice.delegate = self;
[connectedDevice discoverServices:nil]; // this will discover all kind of services
}
If something was wrong during the connection, you will find here (for example, low battery)
- (void)centralManager:(CBCentralManager *)central didFailToConnectPeripheral:(CBPeripheral *)peripheral error:(NSError *)error{
NSLog(#"Did fail to connect: %#",error.description);
connectedDevice = nil;
}
Something went wrong with a successfully connected BLE (for example, low battery, user turned off the device)
- (void)centralManager:(CBCentralManager *)central didDisconnectPeripheral:(CBPeripheral *)peripheral error:(NSError *)error{
NSLog(#"Disconnected: %#",error.description);
connectedDevice = nil;
}
Here, you can find the available services
- (void)centralManager:(CBCentralManager *)central didDiscoverPeripheral:(CBPeripheral *)peripheral advertisementData:(NSDictionary *)advertisementData RSSI:(NSNumber *)RSSI {
NSLog([NSString stringWithFormat:#"%#",[advertisementData description]]);
}
6.
- (void)centralManagerDidUpdateState:(CBCentralManager *)central{
NSString *messtoshow;
switch (central.state) {
case CBCentralManagerStatePoweredOn:
{
[NSString stringWithFormat:#"Bluetooth is currently powered on and available to use."];
CBUUID *heartRate = [CBUUID UUIDWithString:HRM_SERVICE_UUID];
CBUUID *batteryLevel = [CBUUID UUIDWithString:BATTERY_LIFE_SERVICE_UUID];
NSDictionary *scanOptions = [NSDictionary dictionaryWithObject:[NSNumber numberWithBool:NO] forKey:CBCentralManagerScanOptionAllowDuplicatesKey];
[self.centralManager scanForPeripheralsWithServices:[NSArray arrayWithObjects:heartRate,batteryLevel,nil] options:scanOptions];
break;
}
}
}
From now on, you can implement the CBPeripheralDelegate methods
- (void)peripheral:(CBPeripheral *)peripheral didDiscoverServices:(NSError *)error
{
for (CBService *service in peripheral.services) {
NSLog(#"Discovered service: %#", service.UUID);
[peripheral discoverCharacteristics:nil forService:service];
}
}
- (void)peripheral:(CBPeripheral *)peripheral didDiscoverCharacteristicsForService:(CBService *)service error:(NSError *)error
{
if ([service.UUID isEqual:[CBUUID UUIDWithString:HRM_SERVICE_UUID]]) {
for (CBCharacteristic *aChar in service.characteristics)
{
if ([aChar.UUID isEqual:[CBUUID UUIDWithString:HRM_MEASUREMENT_CHARACTERISTIC_UUID]]) {
[connectedDevice setNotifyValue:YES forCharacteristic:aChar];
}
}
}
if ([service.UUID isEqual:[CBUUID UUIDWithString:BATTERY_LIFE_SERVICE_UUID]]) {
for (CBCharacteristic *aChar in service.characteristics)
{
if ([aChar.UUID isEqual:[CBUUID UUIDWithString:BATTERY_LEVEL_CHARACTERISTIC_UUID]]) {
[connectedDevice readValueForCharacteristic:aChar];
}
}
}
}
- (void)peripheral:(CBPeripheral *)peripheral didUpdateValueForCharacteristic:(CBCharacteristic *)characteristic error:(NSError *)error
{
NSError* err = nil;
if ([characteristic.UUID isEqual:[CBUUID UUIDWithString:HRM_MEASUREMENT_CHARACTERISTIC_UUID]]) {
NSData *data = [characteristic value];
}
if ([characteristic.UUID isEqual:[CBUUID UUIDWithString:BATTERY_LEVEL_CHARACTERISTIC_UUID]]) {
}
}
This should work fine. I've implemented it in the same way, and there isn't any problem. I hope this helps.