Lyra 24 Series Bluetooth 5.4 Solutions

When making a connection to a mobile device using Lyra VSP service there is a 15 second delay between the "Ring" indication and the "Connect" indication. This issue is not actually a firmware issue and more of a use case issue. In a scenario whereby two LYRAs are connecting the central LYRA will kickstart the process and once a BT connection is established a series of commands will be sent to the peripheral LYRA to ensure the VSP is ready. These things include writing the Modem in & out descriptors to ensure that the devices are in a good state to send data (set to '1') and also to enable notifications on the Modem out and TX characteristics so that the central can view the incoming data. 

In the case where a different non-LYRA device is acting as a central for a VSP connection these extra commands are not automatically sent therefore it is the central devices responsibility to send these commands. 

Writing to the Modem In characteristic is the write that specifically breaks the peripheral LYRA out of the delay state and to output the connect message. This does not necessarily mean that the VSP system is ready the other commands must also be sent for the system to work properly.

If the 15 second delay is not tolerable for an application, then simply writing any value to the MODEM_IN Characteristic will allow the connection handshake to proceed. For example, using nRF Connect to connect to the Lyra DVK running VSP and connected to a UwTerminalX terminal, a simple write of 0xFF results will then show connect.

Lyra modules must be preloaded with AT Interface firmware, while BL65x modules must be updated to the most current smartBASIC firmware version and programmed with the AT Interface smartBASIC sample application in order to use any AT Interface commands.

To configure a static passkey using AT Interface it is necessary to ensure that the I/O capability of the modules will result in Passkey Entry authentication (per the Bluetooth SIG's IO Capabilities mapping). The Lyra or BL65x module must be configured with the I/O Capability set to Keyboard Only (2) or Keyboard + Display (4), via S Register 107, using the command, ATS 107=x, where x=2 for Keyboard Only or x=4 for Keyboard + Display.

Then the "AT+PKEY " command can be used to issue a static passkey to the underlying stack for use during a pairing procedure in future connections. The passkey must be a 6-digit integer in the range of 000000 – 999999.

The pairing will still use LESC Diffie-Hellman based exchanges.  If a randomly generated number is used for the passkey the static passkey will be used.

Note: Pairing using a pre-programmed passkey makes pairing vulnerable to MITM attacks.

For more information on AT Interface configurations please reference the AT Interface User Guide for the specified module series.

User Guide - BL65x AT Interface Application

User Guide - AT Interface Application - Lyra Series

The AT+PKEY nnnnnn command, used by AT Interface to configure a static passkey, is an on-the-fly command and will not be persistent through a power-cycle/reset. Only S Register settings, using the ATS & AT%S commands, can be saved using AT&W followed by ATZ. All other AT commands are on-the-fly.

NOTE: Using a static, pre-programmed, passkey makes pairing vulnerable to MITM attacks.

For additional information on configuring a static passkey with AT Interface please refer to the appropriate AT Interface User Guide for the Laird Connectivity module you are working with linked below:

User Guide - AT Interface Application - Lyra Series

User Guide - AT Interface Application - BL65x 

These instructions are intended for Linux or Macintosh OS. They may work using WSL, Cigwin, or other bash style terminals in Windows although this is untested. 

It may be desired to communicate with a device attached to the USB-SWD without terminal emulation, I.E. Picocom, Screen, Putty.  This can be useful for writing bash scripts, or if you're using Zephyr's "west flash" and would like a quick way to check your output. 

1. Verify you have the program "stty" available using the command "which stty", if this does not return a value you will need to install it.  Fortunately "stty" generally comes standard with Linux and MacOS.  
2. Identify your serial device.  This can be done using the command "dmesg -w" then connecting the USB-SWD.  You will see output like this (In Linux).

3. (Optional) Assign the device name to a variable, for example "DEVICE=/dev/ttyACM0".
4. Configure "stty" to talk with the device "stty -F $DEVICE 115200 -echo -echoe -echok"
5. To see output from the device execute "cat $DEVICE &".  This will send serial communication from the device to Linux's standard output.  The "&" is to run this program in the background.
6. Now press the reset button on the USB-SWD, you should see the output from your device.  In this example the Zephyr "Hello World" example has been flashed to a BT510. 

7. (Optional) if you would like to send commands back to the device you can use "echo" or add an argument to your shell, "foo() { echo -n -e "$1\r" > $DEVICE; }".  Now commands can be issued directly from the command line, for example "foo "my_command"" will send the string "my_command" to the device. 

Laird Connectivity is committed to the long-term supply of all its standard embedded wireless modules and packaged products. Laird Connectivity’s products are specifically designed to meet the needs of the industrial and medical markets, which typically require 7 – 10 years product lifecycle. Although Laird Connectivity can’t guarantee that a component used in our products will not be obsoleted and cannot be reasonably substituted, Laird Connectivity can assure customers we will continue to sell our product when we have customer demand and can obtain the necessary components to build our products.

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