Issue in Bluetooth pairing

Question

We are testing Bluetooth in WEC2013 with a USB based dongle from generic vendor on iMx6 platform. We are using the default HCI Transport layer provided with WEC2013 BSP.

BT is turned on and able to scan all the nearby devices.

We have enabled following set of sysgen variables and registry entry.

Sysgen Variables:

SYSGEN_BTH (Bluetooth stack with universal loadable driver)
SYSGEN_BTH_BTHUTIL (Bluetooth Profile Management APIs)
SYSGEN_BTH_HID_KEYBOARD (Bluetooth HID - Keyboard)
SYSGEN_BTH_HID_MOUSE (Bluetooth HID - Mouse)
SYSGEN_BTH_AG (Bluetooth HS/HF and Audio gateway service)
SYSGEN_BTH_SETTINGS (Bluetooth settings UI)
SYSGEN_OBEX_CLIENT (Obex client)
SYSGEN_OBEX_SERVER (Obex server)
SYSGEN_OBEX_FILEBROWSER (OBEX file browser)
SYSGEN_OBEX_INBOX (OBEX Inbox)
SYSGEN_FTPD (FTP server)
SYSGEN_BTH_BTHSSVC(Support Secure Simple Pairing)

Registry entry:

[HKEY_LOCAL_MACHINE\Drivers\USB\LoadClients\Default\224_1_1\Default\Bluetooth_USB_Driver]
  "DLL"="bthusb.dll"

[HKEY_LOCAL_MACHINE\Drivers\USB\LoadClients\Default\Default\224_1_1\Bluetooth_USB_Driver]
  "DLL"="bthusb.dll"

[HKEY_LOCAL_MACHINE\Software\Microsoft\Bluetooth\Transports\PnP\{B3DD867A-1E6E-4215-8AA7-EAC1DFC46548}]
"flags"=dword:80000000
"driver"="bthusb.dll"
"resetdelay"=dword:0
"PacketSize"=dword:200
"BlockSize"=dword:5

[HKEY_LOCAL_MACHINE\ControlPanel\Bluetooth]
"PinAttemptInterval"=dword:200000
"PinEntries"=multi_sz:"0000","8888"

We observed different scenario's in pairing to a device.

1. Connecting to mobile from board(imx6+usb dongle running with WEC2013) Here pairing is success when pair is initiated through bthsettings UI. It will trigger the 6-digit automated passkey on both the sides.

2. Connecting from mobile to board without opening bthsettings UI. Here pairing is success once. When the UI is not open (BT is ON in background), pairing is initiated from mobile, both will be paired using automated 6-digit passkey method. But this will internally invoke bthsettings UI, so next time when we give pairing from mobile, mobile side will ask for manual key insertion. As soon as the key is entered on mobile and pair is pressed, pairing rejected notification will be observed on mobile terminal. So pairing is failed in this case.

3. Connecting from mobile to board when bthsettings is opened. Here pairing is failed. When pair is initiated from mobile, manual key insertion UI will be invoked and when key is inserted and pair is pressed, pairing rejected notification will be displayed on mobile terminal and pairing is failed.

In these failed senarios, the upper layer is responding with "Pin code request negative reply command" for "Pin code request event" from chip.

We need input on this pairing process. Why this automated key and manual key generation methods are invoked based on whether UI is open or never opened? And why manual key case is failing?

Are we missing any registry entry or stack feature ?

Answer 1

It all got to do with SSP(Secured Simple Pairing), which decides the pairing authentication model. This is affected in WEC8(2013) through the changes under bthsettings.

Under WEC8 they disable SSP(via function EnbaleSSP()) whenever a connection is initiated from external device and enable back SSP when conenction is initiated internally. Though this is the logic, I'm not aware of why this is introduced(and is it a bug, that'll be fixed in upcoming updates as they initially did for NDIS 5 wireless driver connection).

And as a workaround to this, disable EnableSSP().

Also SYSGEN_BTH_BTHSSVC is implicitly needed by SYSGEN_BTH_SETTINGS component, and the link is broken under WEC8.

Microsoft has provided the fix in April 2015 update. Details available here.