iOS COREBLUETOOTH:write crc commands to peripheral device - ios

Question

i am developing app related to bluetooth my iOS device act as a central and watch act as a peripheral.In order to get some response from the watch i need to give some commands to the watch so that it gives info back i have written the following code
- (void)peripheral:(CBPeripheral *)peripheral didUpdateValueForCharacteristic:
(CBCharacteristic *)characteristic error:(NSError *)error
{
NSString *characteristicUUIDstring = TRANSFER_CHARACTERISTIC_UUID;
CBUUID *characteristicUUID = [CBUUID
UUIDWithString:characteristicUUIDstring];
int comm[6];
comm[0]=0x01;
comm[1]=6;
comm[2]=0x53;
comm[3]=0x00;
comm[4]=0xFFFF;
comm[5]=0xFFFF;
NSMutableArray *arr=[[NSMutableArray alloc]initWithCapacity:4];
for (int i = 0; i < 4; i++) {
NSNumber *number = [NSNumber numberWithFloat:comm[i]];
[arr addObject:number];
}
NSLog(#"mutable arr is %#",arr);
NSString *error1;
NSData *dataarr = [NSPropertyListSerialization dataFromPropertyList:arr
format:NSPropertyListBinaryFormat_v1_0 errorDescription:&error1];
NSUInteger len = [dataarr length];
Byte *byteData = (Byte*)malloc(len);
memcpy(byteData, [dataarr bytes], len);
short crc = (short) 0xFFFF;
for (int j = 0; j < [arr count]; j++)
{
Byte c = arr[j];
for (int i = 7; i >= 0; i--)
{
BOOL c15 = ((crc >> 15 & 1) == 1);
BOOL bit = ((c >> (7 - i) & 1) == 1);
crc <<= 1;
if (c15 ^ bit)
{
crc ^= 0x1021; }
}
}
int crc2 = crc - 0xffff0000;
byteData[0] = (Byte) (crc2 % 256);
byteData[1] = (Byte) (crc2 / 256);
NSLog(#"byte data 1is %hhu",byteData[0]);
NSLog(#"byte data 2is %hhu",byteData[1]);
int com[6];
com[0]=0x01;
com[1]=6;
com[2]=0x53;
com[3]=0x00;
com[4]=byteData[0];
com[5]=byteData[1];
NSMutableArray *sendarr=[[NSMutableArray alloc]initWithCapacity:6];
for (int i = 0; i < 6; i++) {
NSNumber *number = [NSNumber numberWithFloat:comm[i]];
[sendarr addObject:number];
}
NSLog(#"mutable arr is %#",sendarr);
// NSData *data = [NSData datawith:&dataByte length:1];
CBMutableCharacteristic *testCharacteristic =
[[CBMutableCharacteristic alloc] initWithType:characteristicUUID
properties:CBCharacteristicPropertyRead|CBCharacteristicPropertyWrite
value:sendarr
permissions:CBAttributePermissionsReadable|CBAttributePermissionsWriteable];
NSLog(#"Read or Write %# ",testCharacteristic);
[peripheral writeValue:dataarr forCharacteristic:testCharacteristic
type:CBCharacteristicWriteWithResponse];
}