Hi, I would like to discuss the implementation of the GAP discovery and connection establishment for LE. I will focus only on the Central role, which is the role we are actively working on at the moment. Also I'm only talking about the new "mgmt" API. Most of the discussed implementation is not yet upstream (they are on our "developer" trees on gitorious.org and infradead.org), but we are in the process of upstreaming it. Device Discovery: For dual mode (BR/EDR/LE) adapters, discovery is interleaved between BR/EDR and LE. This procedure is documented on Core spec, Vol. 3 [Part C], Section 13.2.1. For single mode adapters (although we have no working single mode adapter), LE only discovery is used, as described on Vol. 3 [Part C], Section 9.2.6. Note that only "General Discovery" is supported. We don't support Limited Discovery. Name discovery: not supported (both BR/EDR and LE) Connection establishment (over LE): "Direct Connection Establishment" procedure is followed, with these parameters: Scan interval: 2.5ms Scan window: 2.5ms Conn_Interval_Min: 5ms Conn_Interval_Max: 160ms Supervision timeout: 62.5ms (this is incorrect, it shall be larger than Conn_Interval_Max) Unsupported features ================== Now that the Thermometer GATT profile has been approved, anyone can take a look at the "Connection Establishment" section of https://www.bluetooth.org/docman/handlers/downloaddoc.ashx?doc_id=238687 and notice the following: "The Collector should use the GAP Limited Discovery Procedure to discover a Thermometer." We currently do not support limited discovery. "A Collector may use one of the following GAP connection procedures based on its connectivity requirements: [...]" We support only the Direct Connection Establishment Procedure. "The Collector should use the recommended scan interval and scan window values shown in Table 5.2. [...]" Our scan interval/window values are very different from the recommended ones (too small). I think this should be fixed. "For the first 30 seconds [...], the Collector should use the first scan window / scan interval pair to attempt fast connection. However, if a connection is not established within that time, the Collector should switch to one of the other scan window / scan interval options as defined below to reduce power consumption." We only attempt the connection once, using a fixed set of parameters. Maybe this needs to be changed to follow the recommendations above. Note that there are two "reduced power" configurations. "The Collector shall start encryption after each connection creation to verify the status of the bond. [...]" We don't require encryption, it is optional (by setting the security level to medium or high). "When a connection is terminated due to link loss, a Collector should attempt to reconnect to the Thermometer" We don't support automatic reconnection (yet). "The Collector may perform the GAP Terminate Connection procedure if the connection is idle for more than 5 seconds." We don't have such timer (is it specific to the Thermometer profile?) "To avoid very long service discovery and encryption times, the Collector should use the connection intervals defined in Table 5.3 in the connection request." We use fixed connection interval values during the entire connection. "This fast connection interval should be maintained as long as low latency is required. After that, it should switch to the preferred connection parameters as decided by the Thermometer using the GAP Connection Parameter Update procedure." We seem to support connection parameter update requests. Comments are welcome! Best Regards, -- Anderson Lizardo Instituto Nokia de Tecnologia - INdT Manaus - Brazil -- 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
