[Bluez-users] reading RSSI value with D-Bus Api

[Bluez-users] reading RSSI value with D-Bus Api

[Emanuele Novelli]

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Hello,
reading another post here, I saw Marcel hinted to use the inquiry from D-Bus
API to sort the devices by their RSSI so I tried a simple test

this is the part of code I'm using
...

 if (dbus_message_is_signal(msg, "org.bluez.Adapter",
"RemoteDeviceFound")) {
          printf ("Remote Device Found Signal Received\n");

             while (dbus_message_iter_get_arg_type(&iter)  !=
DBUS_TYPE_INVALID)  {
                 switch (dbus_message_iter_get_arg_type(&item)) {
                     case DBUS_TYPE_STRING:  /* first pameter bdaddress */
                      .....

                     break;
                     case DBUS_TYPE_UINT32: /* second parameter class of
device */
                     ........
                    break;

                     case DBUS_TYPE_INT16: /* rssi */
                         dbus_message_iter_get_basic(&args, &rssi);
                         printf("rssi: %d\n", rssi);
                         break;

......



Now the problem is: I can read the bdaddress and the device class good, but
the RSSI values I get from variuous devices are negatives (the are in range
-40 -90 usually). I read somewhere RSSI should range from 0 to 255 so maybe
I'm doing something wrong ? api says the type RSSI is int16 not uint16 so I
used a signed variable.

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Re: [Bluez-users] reading RSSI value with D-Bus Api

[Marcel Holtmann]

Hi Emanuele,

> reading another post here, I saw Marcel hinted to use the inquiry from
> D-Bus API to sort the devices by their RSSI so I tried a simple test
> 
> this is the part of code I'm using
> ...
> 
>  if (dbus_message_is_signal(msg, " org.bluez.Adapter",
> "RemoteDeviceFound")) {
>           printf ("Remote Device Found Signal Received\n");
>          
>              while (dbus_message_iter_get_arg_type(&iter)  !=
> DBUS_TYPE_INVALID)  { 
>                  switch (dbus_message_iter_get_arg_type(&item)) {
>                      case DBUS_TYPE_STRING:  /* first pameter
> bdaddress */
>                       .....
>        
>                      break;
>                      case DBUS_TYPE_UINT32: /* second parameter class
> of device */
>                      ........ 
>                     break;  
>                      
>                      case DBUS_TYPE_INT16: /* rssi */ 
>                          dbus_message_iter_get_basic(&args, &rssi);
>                          printf("rssi: %d\n", rssi);
>                          break;
>                      
> ......
> 
> 
> 
> Now the problem is: I can read the bdaddress and the device class
> good, but the RSSI values I get from variuous devices are negatives
> (the are in range -40 -90 usually). I read somewhere RSSI should range
> from 0 to 255 so maybe I'm doing something wrong ? api says the type
> RSSI is int16 not uint16 so I used a signed variable. 

the RSSI value is a signed int8 actually (except that D-Bus doesn't
support this type). You might confuse this with the link quality value,
but the RSSI is always signed.

Regards

Marcel



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Re: [Bluez-users] reading RSSI value with D-Bus Api

[Emanuele Novelli]

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Hi Marcel,

I'm referring to this function (from bluez dbus-api) where the rssi
parameter is int16

----
void RemoteDeviceFound(string address, uint32 class, int16 rssi)

            This signal will be send every time an inquiry result
            has been found by the service daemon. In general they
            only appear during a device discovery.
----

you posted in another thread you can use that value to check how close is
the remote device to the dongle who does inquiry. Maybe I'm wrong and that's
not the correct value to check for this purpose?
Anyway the third parameter I read with the snipped code I posted is
negative.

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Re: [Bluez-users] reading RSSI value with D-Bus Api

[Mahtab Hossain]

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Hi Emanuele,
Sometimes, the Bluetooth module vendor provides absolute signal strength (like Wi-Fi) rather than the relative RSSI value indicated in Bluetooth Spec. I had one dongle which did just that. You may need to send your inquiry to them as well if it's really the case.

Thanks
Mahtab

Emanuele Novelli <ema.novelli@gmail.com> wrote: Hi Marcel,

I'm referring to this function (from bluez dbus-api) where the rssi parameter is int16

----
void RemoteDeviceFound(string address, uint32 class, int16 rssi)

            This signal will be send every time an inquiry result 
            has been found by the service daemon. In general they
            only appear during a device discovery.
----

you posted in another thread you can use that value to check how close is the remote device to the dongle who does inquiry. Maybe I'm wrong and that's not the correct value to check for this purpose? 
Anyway the third parameter I read with the snipped code I posted is negative.

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Re: [Bluez-users] reading RSSI value with D-Bus Api

[Mahtab Hossain]

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Hi Emanuele,
Sometimes, the Bluetooth module vendor provides absolute signal strength (like Wi-Fi) rather than the relative RSSI value indicated in Bluetooth Spec. I had one dongle which did just that. You may need to send your inquiry to them as well if it's really the case.

Thanks
Mahtab

Emanuele Novelli <ema.novelli@gmail.com> wrote: Hi Marcel,

I'm referring to this function (from bluez dbus-api) where the rssi parameter is int16

----
void RemoteDeviceFound(string address, uint32 class, int16 rssi)

            This signal will be send every time an inquiry result 
            has been found by the service daemon. In general they
            only appear during a device discovery.
----

you posted in another thread you can use that value to check how close is the remote device to the dongle who does inquiry. Maybe I'm wrong and that's not the correct value to check for this purpose? 
Anyway the third parameter I read with the snipped code I posted is negative.

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Re: [Bluez-users] reading RSSI value with D-Bus Api

[Mahtab Hossain]

[-- Attachment #1.1: Type: text/plain, Size: 1626 bytes --]

Hi Emanuele,
Sometimes, the Bluetooth module vendor provides absolute signal strength (like Wi-Fi) rather than the relative RSSI value indicated in Bluetooth Spec. I had one dongle which did just that. You may need to send your inquiry to them as well if it's really the case.

Thanks
Mahtab

Emanuele Novelli <ema.novelli@gmail.com> wrote: Hi Marcel,

I'm referring to this function (from bluez dbus-api) where the rssi parameter is int16

----
void RemoteDeviceFound(string address, uint32 class, int16 rssi)

            This signal will be send every time an inquiry result 
            has been found by the service daemon. In general they
            only appear during a device discovery.
----

you posted in another thread you can use that value to check how close is the remote device to the dongle who does inquiry. Maybe I'm wrong and that's not the correct value to check for this purpose? 
Anyway the third parameter I read with the snipped code I posted is negative.

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Re: [Bluez-users] reading RSSI value with D-Bus Api

[Mahtab Hossain]

[-- Attachment #1.1: Type: text/plain, Size: 1633 bytes --]

Hi Emanuele,
Sometimes, the Bluetooth module vendor provides absolute signal strength (like Wi-Fi) rather than the relative RSSI value indicated in Bluetooth Spec. I had one dongle which did just that. You may need to send your inquiry to them as well if it's really the case.

Thanks
Mahtab

Emanuele Novelli <ema.novelli@gmail.com> wrote: Hi Marcel,

I'm referring to this function (from bluez dbus-api) where the rssi parameter is int16

----
void RemoteDeviceFound(string address, uint32 class, int16 rssi)

            This signal will be send every time an inquiry result 
            has been found by the service daemon. In general they
            only appear during a device discovery.
----

you posted in another thread you can use that value to check how close is the remote device to the dongle who does inquiry. Maybe I'm wrong and that's not the correct value to check for this purpose? 
Anyway the third parameter I read with the snipped code I posted is negative.

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