Bluetooth GATT Handle to UUID Mapping
# helpz
z3ugma
04/21/2024, 5:48 PMAt https://libs.toit.io/ble/class-RemoteCharacteristic the docs describe a BLE GATT characteristic and let you access the UUID of the characteristic.
Separately is the concept of a BLE
handlehandleuuidf
floitsch
04/21/2024, 5:51 PMI recently worked on the BLE library again but I didn't see any reference to the term "handle". My first instinct is that the handle is not exposed. I would need to look at the code to know more.
floitsch
04/21/2024, 5:51 PMThe BLE code is based on nimble. So maybe you can find more information there.
z
z3ugma
04/21/2024, 5:54 PMCheck out something like https://stackoverflow.com/questions/75428882/trying-to-understand-ble-uuids-and-handles-with-bluetoothctl-example
when first interrogating a BLE device, a mapping of the handle to the UUID is maintained.
When you sent the actual BLE packet, it references the handle and not the UUID
z3ugma
04/21/2024, 5:55 PMnimBLE has
RemoteCharacteristic::getHandle().z3ugma
04/21/2024, 5:56 PMwhich is similar to the
Copy code
NimBLEUUID NimBLERemoteDescriptor::getUUID ( )f
floitsch
04/21/2024, 5:56 PMThe uuid is part of the characteristic. No?
floitsch
04/21/2024, 5:56 PMThat's how it is referenced.
z
z3ugma
04/21/2024, 5:57 PMthe characteristic has 2 properties: a uuid and a handle
z3ugma
04/21/2024, 5:58 PMRemoteCharacteristic::getHandle()
RemoteCharacteristic::getUUID()
^^ 2 different attributes that nimBLE lets you fetch with regard to a given characteristic
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floitsch
04/21/2024, 6:00 PMI intend to work on the BLE library tomorrow. I will read up on handles then.
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z3ugma
04/21/2024, 6:23 PMcool!
During the initial connection when you discover the services and characteristic, the BLE packet that is sent is called
use the BLE opcode : Read By Type Request (0x08)
which matches up the Handle to the UUID
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floitsch
04/21/2024, 6:34 PMI'm not yet familiar with the handles, but what does that mean for Toit?
Do we do it right or wrong? Is something still missing.
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z3ugma
04/22/2024, 2:28 PMyes - right now, I need to send a write command to a characteristic GATT UUID.
If I know the handle but not the UUID, then it's a bunch more debugging to figure out which handle matches up to which UUID
if I know the handle, it would be nice to directly be able to identify a characteristic by its handle instead of by its UUID
z3ugma
04/22/2024, 2:30 PMWhile we are at it:
BLE's L2CAP protocol allows a packet to say if it expects more data
https://cdn.discordapp.com/attachments/1231662744839651378/1231975350859202733/image.png?ex=6638e974&is=66267474&hm=c461a3bc87063e21c38679cac5da2985cef27d9f89c8053958639fda09988e54&
z3ugma
04/22/2024, 2:30 PMthat would also be really nice to implement when subscribing to a GATT, to know if we need to await an additional packet
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floitsch
04/22/2024, 2:54 PMOk.
floitsch
04/22/2024, 2:55 PMI have been working on the BLE library the whole day, and will probably continue to do so tomorrow as well.
I will see if I can expose the handle and the 'more data' flag. (assuming that's what it is).
floitsch
04/23/2024, 5:07 PMI have uploaded a PR for the handles, but I couldn't find any information on how to get to the "More Data" header field.
If you know how to get to it in nimBLE/ESP-IDF I can have another look.
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Informatic0re
04/26/2024, 9:22 AMcould the "more data" be the manufacturer data which you can add to the service?
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floitsch
04/26/2024, 9:44 AMReally don't know, but even if it is: I would need the nimble function to somehow expose it.
i
Informatic0re
04/26/2024, 9:45 AMthe manufacturer part is already in the ble library. but I am also not sure what this "more data" part might be
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