On Tue, Aug 3, 2010 at 00:09, Marcel Holtmann <marcel@xxxxxxxxxxxx> wrote: > Hi Davide, > >> >> >> I'm writing an application to retrieve the current link quality (or >> >> >> RSSI) between my laptop's Bluetooth adapter and a specific remote >> >> >> device (my mobile phone). In order to do that I'm of course using the >> >> >> latest version of BlueZ, but I've encountered several issues so far. >> >> >> >> >> >> The dbus API exposed by bluetoothd doesn't have any GetRSSI or >> >> >> GetLinkQuality methods. Would it be possible to export these methods >> >> >> in the public API? >> >> > >> >> > the link quality is vendor specific according to the specification and >> >> > the RSSI of an existing connection is rather useless. So we don't bother >> >> > to export those. >> >> > >> >> >> >> Does this mean you're going to reject a patch which adds those methods >> >> to the dbus API? >> > >> > constantly polling them via D-Bus, yes I would reject such a patch. To >> > make this proper you would need a kernel patch first that polls the RSSI >> > and/or link quality when a ACL is established and not in power saving >> > mode. Then you need to use this data to send async signals via D-Bus. >> > >> > I have done both, let me assure you that some chips don't provide proper >> > RSSI values. Then link quality is vendor specific and we can't do >> > anything real useful with it (except it is a CSR chip). So I have don't >> > the whole exercise and figured out that it is rather useless feature of >> > Bluetooth. >> > >> >> >> Then I looked at the bluetooth HCI library that comes with bluez. >> >> >> First of all, is there any reasons why it's totally undocumented? >> >> >> Anyway, I noticed hci_read_link_quality() and hci_read_rssi() in >> >> >> hci_lib.h and tried using them. Since they seem to require an >> >> >> established connection, I also used hci_create_connection(). However I >> >> >> soon discovered that creating a connection requires root privileges, >> >> >> is that right or did I do something wrong? >> >> >> >> >> >> Furthermore, even when running the program as root, the connection >> >> >> gets established only for a few seconds and then it disconnects from >> >> >> the remote device. Is this behaviour intended? How can I specify to >> >> >> keep the connection alive indefinitely? >> >> > >> >> > If you don't have an active connection that is used, the kernel will >> >> > terminate any idle ones. So using hcitool for this is rather pointless >> >> > unless you have a profile already using that connection. >> >> > >> >> >> >> "using a connection" means pushing some traffic over it? >> >> Is there no other way to prevent the kernel from terminating idle connections? >> > >> > You don't need to transfer data, but you need a reference count on the >> > ACL link. And that can only happen by opening a L2CAP socket. >> > >> >> By the way, I've read in the Bluetooth specs that there exists an >> >> extended inquiry mode which allows the host to gather the RSSI of >> >> available devices too. How can I perform such kind of inquiry from my >> >> application using bluez? >> > >> > Nice idea, but RSSI from inquiry result and RSSI from an ACL are not the >> > same. You can't compare them properly to make sense out of them. I tried >> > that as well. Please read the specification again to see their >> > difference when it comes to power control on the low level baseband. >> > >> >> Well, that's a non-issue. If I decide to go that way, I'll only use >> RSSI from inquiry results so I don't need to compare RSSI values >> coming from different sources. >> How could I trigger an inquiry with RSSI reporting? > > that is one by default if the hardware supports it. > Very nice! I quickly checked using qdbusviewer and it does seem to work. Thanks a lot for you help! Regards, Davide -- To unsubscribe from this list: send the line "unsubscribe linux-bluetooth" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
