BLE does not read whole buffer data

[livius]

@livius
I do not know much about sources but maybe someone know how to debug this
how can i send something to UART from e.g.
BTA_GATTC_GetAllChar or bta_gattc_get_db_with_opration
https://github.com/pycom/pycom-esp-idf/blob/master/components/bt/bluedroid/bta/gatt/bta_gattc_cache.c

[jmarcelino]

Hi @livius ,
The Bluetooth 4.1 spec only allows up to 31 bytes of LE advertising data (39 bytes maximum LL PDU packet composed of 2 bytes of header + 6 bytes of device address + 31 bytes of Advertising Data (AD)

Anything above that gets truncated in the stack.

[livius]

@jmarcelino
then why all scanners which i have got whole buffer?
Do you think that all are in BT4.2?

[jmarcelino]

@livius
I don know what devices you're trying to read from and what the scanner is but I think that it's unlikely they're all 4.2 devices.

Probably they combine advertising data and scan response somehow?

[livius]

@jmarcelino
I see that MI BAND 2 is BLE4.2 device.
and it follow spec
http://microchipdeveloper.com/wireless:ble-link-layer-packet-types

[jmarcelino]

@livius
It's not possible to send such a long advertising packet even in Bluetooth 4.2, you'd need Bluetooth 5 (with LE Advertising Extensions) for that.

If you look up that Microchip reference the Advertising Channel PDUs have a 0-37 bytes Payload and you need the device address on top (6 bytes) on that so the maximum actual data is 31 bytes.

If you are seeing longer packets it's probably because your BLE scanner combines the result of the advertising packet with the scan response.

[livius]

@jmarcelino
Thank you Jose i am new in BLE protocol and must dig more.
But this will be strange if BLE4.2 device will advertise in mixed protocol
I suppose that your last sentence is much more possible.

[livius]

@livius
It really combine SCAN_RSP packet.
And now i have question, how can i make active scan with wipy2.
Because i understand that 'start_scan' do passive scan only?

[jmarcelino]

@livius
The current scan is active: https://github.com/pycom/pycom-micropython-sigfox/blob/eca3b714a11c4b84e740a36b4096a20aac3c9be2/esp32/mods/modbt.c#L271

but we don't combine the scan response, only show advertising data.

[livius]

@jmarcelino
Is there possibility to got scan response data somehow then?

[jmarcelino]

@livius
That's not available yet, sorry

[livius]

@jmarcelino
thank you for that info.
I will dig into sources if something can be done self here.

[tudro]

@jmarcelino +1 to have the scan reponse available :) thank you

[livius]

@jmarcelino
I see that in public firmware it is now also avaiable :)

(mac=b'\xd2lBk\xad\xc2', addr_type=1, adv_type=0, rssi=-83, data=b'\x02\x01\x06\x1b\xffW\x01\x00\xef\xbf\xc9\xac\xe7\xd5\xd0.\xe5\xf0\x8cr[\x8b[w\x03\xd2lBk\xad\xc2\n\tMI Band 2\x03\x02\xe0\xfe\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00') {'NameShort': None, 'Flag': 6, 'Mac': b'd26c426badc2', 'NameComplete': b'4d492042616e642032', 'MfrData': b'570100efbfc9ace7d5d02ee5f08c725b8b5b7703d26c426badc2', 'Data': b'0201061bff570100efbfc9ace7d5d02ee5f08c725b8b5b7703d26c426badc20a094d492042616e6420320302e0fe00000000000000000000000000000000', 'Rssi': -83, 'Appearance': None}

'NameComplete': b'4d492042616e642032'

import binascii
a=b'4d492042616e642032'
c=binascii.unhexlify(a)
print(c)

give me proper result :)
'MI Band 2'