Re: [RFC 3/3] Bluetooth: Add AMP initialization

Hi James,

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actually I think the READ_AMP_INFO is wrong here. It should be only

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executed based on an AMP_Get_Info_Request during a connection setup

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procedure.

 

You can read the AMP info over HCI upon receiving a request by A2MP,
but there are reasons to issue the READ_AMP_INFO command in advance.
For example, you need the Controller_Type for responding to the
AMP_Discover_Request.  Also you may (tenuously) want the know the
Max_PDU_Size in advance for selecting SDU sizes (w.r.t. segmentation).

 

Certainly READ_AMP_INFO is a command intended to be issued during
controller initialization, the majority of the values should not
change during the lifetime of the controller, and only once that
command has been issued will the Controller commence sending
AMP_Status_Change_Events to communicate changes in status.  At a
minimum READ_AMP_INFO must be issued for each AMP_Discover_Request
(and AMP_Get_Info_Request) received; but if AMP discovery is slower,
then transitioning a channel to an AMP link will be slower.

is the AMP_Status_Change event is issued, then I am fine with reading
the AMP controller information ones at init and just caching it. Makes
the link setup procedure simpler since we only have to deal with the
assoc information.

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And even the READ_BUFFER_SIZE is the wrong command since by default

the

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AMP controller is in block based flow control mode. So you would

need to

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read the flow control mode first actually.

 

Correct, although reading the flow control mode on an AMP controller
after a HCI_Reset *should* always return “data block mode” (as that is
the default).  The READ_BUFFER_SIZE should only be used if
HCI_Write_Flow_Control_Mode has been issued first (and successfully
enabled packet based flow control).  Instead I believe we should issue
the HCI_Read_Data_Block_Size command, where the correct information is
then provided for the host stack (with its "new" data block flow
control model for AMP controllers).  I don’t think there is any
requirement forcing an AMP controller to implement packet based flow
control, so if there is no data block flow control model in the host
yet then initialization has to be prepared to fail upon trying to
configure packet based flow control mode.

Reading the flow control mode and data block size should be done via the
init sequence.

Also for AMP Controller initialization, the HCI_Set_Event_Mask_Page_2
command should be issued to ensure the AMP related events are provided
by the controller (by default they are turned off).  A suitable
HCI_Set_Event_Mask command may also be needed if using enhanced flush
on the AMP controller.  Event filters also apply to AMP controllers
IIRC, so if following the BR/EDR example you may want to clear them
too (although I imagine such initialization could be added when
required).

The filters should be cleared by HCI_Reset actually. So we might just
ignore that one. I never found the HCI filters useful, but the event
mask is a good point. We need to set that one.

Regards

Marcel