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I am using Windows 10 build 14393.2156. Bluetooth adapter LMP version is 6.X (Bluetooth version 4.0). I cannot write byte array data with length 350. However, I can write byte array data with length around 60 and get the expected data from the BLE device. When i write byte array of large length e.g. 350, I get windows exception: "Exception: The specified server cannot perform the requested operation. (Exception from HRESULT: 0x8007003A)". Following is the code:

private async Task CoreWrite(byte data)
 
 var writeBuffer = CryptographicBuffer.CreateFromByteArray(data);
 var result = await _txCharacteristic.WriteValueAsync(writeBuffer);
 if (result != GattCommunicationStatus.Success)
 
 throw new IOException($"Failed to write to bluetooth device. Status: nameof(result)");
 
 

Please note that the device is already paired. Is there any payload limit which can possibly affect limiting of payload length in Bluetooth 4.0 versus 4.2 specification. Or you suggest a higher Windows 10 builds with more recent Bluetooth LMP 8.X should help fix the issue. Appreciate any advice or help.

Many thanks.

Surprisingly, we found that Attribute Data Length of the characteristic was limited at 244 bytes. Hence, I was not able to write any data more than 244 bytes. However, performing multiple writes with 244 bytes at a time does resolve this issue. I could see the expected response from the BLE device.

Example:

int offset = 0;
int AttributeDataLen = 244;
while (offset < data.Length)

 int length = data.Length - offset;
 if (length > AttributeDataLen)
 
 length = AttributeDataLen;
 

 byte subset = new byte[length];

 Array.Copy(data, offset, subset, 0, length);
 offset += length;

 var writeBuffer = CryptographicBuffer.CreateFromByteArray(subset);
 var result = await _txCharacteristic.WriteValueAsync(writeBuffer);
 if (result != GattCommunicationStatus.Success)
 
 throw new IOException(
 $"Failed to write to bluetooth device. Status: nameof(result)");