Hi all,
We found iOS may return services and characteristics from cache if our application invoke CBPeripheral::discoverServices().
| 14:59:18.824260 +0800 | bluetoothd | Attempting to find all services on device "<private>" |
| 14:59:18.824785 +0800 | bluetoothd | Returning primary services from cache |
But our product may change the chracteristics attribute handle number after product firmware updated.
For example, FW Ver1: discovered serivce like below,
14:59:18.826036 +0800 bluetoothd Using local database for discover services by UUID.
14:59:18.826926 +0800 bluetoothd statedump: 0x0001 Primary Service [ serviceUUID: -, endHandle: 0x0006, discoveredCharacteristics: all ]
14:59:18.827124 +0800 bluetoothd statedump: 0x0002 Characteristic [ valueUUID: -, valueHandle: 0x0003, properties: notify, discoveredDescriptors: all ]
14:59:18.827412 +0800 bluetoothd statedump: 0x0003 Characteristic Value [ - ]
14:59:18.827549 +0800 bluetoothd statedump: 0x0004 Client Configuration [ none ]
14:59:18.827713 +0800 bluetoothd statedump: 0x0005 Characteristic [ valueUUID: -, valueHandle: 0x0006, properties: responseless-writes write, discoveredDescriptors: none ]
But after FW updated, FW Ver2: discovered service should like below,
15:00:09.204374 +0800 bluetoothd statedump: 0x0001 Primary Service [ serviceUUID: -, endHandle: 0x0006, discoveredCharacteristics: none ]
15:00:09.204613 +0800 bluetoothd statedump: 0x0007 Primary Service [ serviceUUID: -, endHandle: 0x000C, discoveredCharacteristics: none ]
15:00:09.205718 +0800 bluetoothd Finding all characteristics in range [0x0007, 0x000c] on device "<private>"
15:00:09.265822 +0800 bluetoothd statedump: 0x0001 Primary Service [ serviceUUID: -, endHandle: 0x0006, discoveredCharacteristics: none ]
15:00:09.266798 +0800 bluetoothd statedump: 0x0007 Primary Service [ serviceUUID: -, endHandle: 0x000C, discoveredCharacteristics: all ]
15:00:09.267084 +0800 bluetoothd statedump: 0x0008 Characteristic [ valueUUID: -, valueHandle: 0x0009, properties: notify, discoveredDescriptors: none ]
15:00:09.267562 +0800 bluetoothd statedump: 0x000B Characteristic [ valueUUID: -, valueHandle: 0x000C, properties: responseless-writes write, discoveredDescriptors: none ]
But if we didnot power off/on iPhone's Setting >> Bluetooth switch (reset bluetooth), we cannot setNotifyValue() successfuly.
14:59:18.883104 +0800 bluetoothd Received error response for write value 3 (status=65535)
14:59:18.883522 +0800 bluetoothd Failed to write descriptor at handle 0x0004 on device "<private>" - result was 3
How can app force to discover service and characteristic from BLE device but not just from iOS local cache database?
Thank you
To indicate to an Apple device that it should read the services/characteristics directly from the device instead of using the cached values, your peripheral must implement the Device Changed characteristic. This is also mentioned in the Accessory Design Guidelines document.
23.12.2 Generic Attribute Profile Service
The accessory must implement the Service Changed characteristic only if the accessory has the ability to change its services during its lifetime.
The device may use the Service Changed characteristic to determine if it can rely on previously read (cached) information from the device. See the Bluetooth 4.0 specification, Volume 3, Part G, Section 7.1.
