Connect fails immediately if another connect is pending. about bluepy HOT 3 CLOSED

I just tried creating the same situation by running two separate gatttool processes, and had the same result: while one connect is pending, others immediately fail. So presumably this is not a bluepy issue, but something lower level. I'd still love any suggestions on workarounds, fixes, or working-as-intended. Thanks!

from bluepy.

It looks like it's a limitation of Bluetooth LE itself. Connecting to a peripheral is done with the LE_Create_Connection command; the Bluetooth 4.0 spec says (vol 2, sec 7.8.12, page 826)

The Host shall not issue this command when another LE_Create_Connection is pending in the
Controller; if this does occur the Controller shall return the Command Disallowed error code shall
be used.

Sadly, then, it's built in to the HCI command specification that only one connection can be pending at a a time.

Thanks
Ian

from bluepy.

Apologies--I meant to close this myself. In case it is ever of use to anyone else, I also tracked down the kernel code implementing the limitation, and it appears to only limit it to one connection per CID (rather than one globally). Since all my devices are using the Attribute CID (0x04) and I don't really have control over it, I haven't tested whether you can do multiple connections on different channels or the limitation matches the BT4 spec, though I note that the error returned is EBUSY.

Also, note that canceling the connection does allow for new connections, so I'm manually timing out my asynchronous connects after a much shorter period. (I'm also now listening for announcements on another BT dongle and using that to limit connection attempts to missing devices.)

Thanks!

from bluepy.