Hi Adam, On Tue, Mar 22, 2022 at 4:09 PM Adam Pigg <adam@xxxxxxxxxxx> wrote: > > Thanks Luiz > > On Tue, 22 Mar 2022 at 21:35, Luiz Augusto von Dentz > <luiz.dentz@xxxxxxxxx> wrote: > > > > Hi Adam, > > > > On Tue, Mar 22, 2022 at 3:40 AM Adam Pigg <adam@xxxxxxxxxxx> wrote: > > > > > > Hi Luiz > > > > > > > > > On Tue, 22 Mar 2022 at 07:55, Adam Pigg <adam@xxxxxxxxxxx> wrote: > > > > > > > > Hi Luiz > > > > > > > > On Tue, 22 Mar 2022 at 00:44, Luiz Augusto von Dentz > > > > <luiz.dentz@xxxxxxxxx> wrote: > > > > > > > > > > Hi Adam, > > > > > > > > > > On Mon, Mar 21, 2022 at 4:03 PM Adam Pigg <adam@xxxxxxxxxxx> wrote: > > > > > > > > > > > > Hi > > > > > > > > > > > > A bit of background, I write a linux desktop/mobile app called > > > > > > Amazfish which interfaces with several watches over BLE using their > > > > > > GATT services. To do this, I use the bluez dbus api (technically a > > > > > > thin wrapper around it I wrote called qble > > > > > > https://github.com/piggz/qble) > > > > > > > > > > > > All has been good so far, I support several generations of > > > > > > Huami/Amazfit watches, as well as the open source Pinetime and > > > > > > Bangle.js. For the Amazfit watches, i have implementations for older > > > > > > devies such as the Bip, and newer ones such as the GTS. > > > > > > > > > > > > Much of the reverse engineering comes from the Android Gadget Bridge > > > > > > project, which supports many more devices. > > > > > > > > > > > > My community of users donated to buy me a newer device called a GTR2, > > > > > > which, according to the GB devs uses the same protocol as the slightly > > > > > > older GTS, and the packet captures I have from Android would support > > > > > > this. > > > > > > > > > > > > But this is where my trouble starts with Bluez, my existing > > > > > > implementation doesnt work at all. Normally, after a connection, I > > > > > > would wait for the ServicesResolved signal, which happens pretty fast > > > > > > on all other devices, but on the GTR2, it takes about 30 seconds, by > > > > > > which time, the watch has disconnected. (i get a disconnected signal > > > > > > immediately after the ServicesResolved signal) > > > > > > > > > > > > To rule out my code, I have tried several things: > > > > > > Gatttool > > > > > > With gattool, i can connect, get the services, enable a notification, > > > > > > write a value and get the expected results seemingly fine > > > > > > > > > > > > Python-gatt (using the bluez dbus api) > > > > > > Im unable to iterate the services, like my app, it takes 30 seconds to > > > > > > get the signal and then swiftly disconnects > > > > > > > > > > > > Gattlib (https://github.com/labapart/gattlib) > > > > > > Gattlib is interesting as it appears to have "borrowed" much of its > > > > > > code directly from bluez. When built against the system bluez, if the > > > > > > version is > 5.42, it will use the dbus api. When I do this, again im > > > > > > unable to list services on the watch. However, if I edit the build to > > > > > > force it to use its internal gatt implementation, which appears to be > > > > > > the same one used by gatttool, then, it IS able to interrogate the > > > > > > watch. > > > > > > > > > > > > I have attached 3 files > > > > > > 1. test python program which should print services, and associated btmon > > > > > > 2. btmon output while using gatttool > > > > > > 3. btmon output running gattlib discover example > > > > > > > > > > > > Note, other than discovery, I havnt been able to get gattlib to > > > > > > read/write/notify! > > > > > > > > > > > > It seems as though I may be triggering a bug in the bluez dbus api? > > > > > > Can anyone suggest anything? > > > > > > > > > > What version are you using? I would first try with the latest to see > > > > > if that something already fixed. > > > > > > > > > > > > > > Im using 5.63 already, which is the latest tag (on opensuse tumbleweed) > > > > > > > > I'll also try bluetoothctl and attach logs using that, though I > > > > suspect it will behave the same as the python library and my own > > > > library. > > > > > > > > > > Attached is the output of btmon while using bluetoothctl > > > > > > bluetoothctl behaves the same as my lib and python, it is unable to > > > list services, and after a while, emits the ServicesResolved and > > > disconnected messages at the same time. Im sure it should be able to > > > list the services immediately after connect just like gatttool can. > > > > Looks like there is multiple rounds of MTU Exchange, not sure if that > > is actually a problem but the spec does say it shall only be sent once > > per client: > > > > BLUETOOTH CORE SPECIFICATION Version 5.3 | Vol 3, Part F > > page 1424: > > > > This request shall only be sent once during a connection by the client. > > > > There is also no response to frame #30: > > < ACL Data TX: Handle 3585 flags 0x00 dlen 7 > > > > #30 [hci0] 26.641557 > > ATT: Read Request (0x0a) len 2 > > Handle: 0x0018 > > > > So after 30 seconds (ATT timeout) without receiving any response it disconnects: > > > > So, the verdict is that the watch isnt acting to spec right? > > Why does gatttool work ok, is it a completely different implementation? > > I understand if wouldnt be to spec, but would it be possible to make > bluez more resilient to devices not acting to spec? Android and iOS > work just fine in this regard, so could bluez handle mis-behaving > devices more flexibly? That I can't really explain, perhaps it is timing related, something with Exchange MTU since it appears to stop the device from responding when it happens a second time. > Do you have any suggestions for things I could try? I looked for > similar lines in the working gatttool log, and it doesnt have anything > like that, seems to send flags 0x00 dlen 9 (instead of 7?) ... how is > it behaving differently? Not sure really, does Android/iOS Exchange the MTU? Maybe we need a timer to start it later or perhaps the problem first response to exchange MTU does actually use the final_mtu which makes the watch to trigger yet another exchange to have both rx and tx MTU the same so try with the following change: diff --git a/src/shared/gatt-server.c b/src/shared/gatt-server.c index 2adb4afbf..d326782bf 100644 --- a/src/shared/gatt-server.c +++ b/src/shared/gatt-server.c @@ -1499,7 +1499,7 @@ static void exchange_mtu_cb(struct bt_att_chan *chan, uint8_t opcode, final_mtu = MAX(MIN(client_rx_mtu, server->mtu), BT_ATT_DEFAULT_LE_MTU); /* Respond with the server MTU */ - put_le16(server->mtu, rsp_pdu); + put_le16(final_mtu, rsp_pdu); bt_att_chan_send_rsp(chan, BT_ATT_OP_MTU_RSP, rsp_pdu, 2); /* Set MTU to be the minimum */ > > > < HCI Command: Disconnect (0x01|0x0006) plen 3 > > > > #48 [hci0] 58.673128 > > Handle: 3585 > > Reason: Remote User Terminated Connection (0x13) > > > > > Thanks > > > > > > > > > > > -- > > > > > Luiz Augusto von Dentz > > > > > > > > -- > > Luiz Augusto von Dentz -- Luiz Augusto von Dentz
