Determine the Operating Mode of the BLE Device

In the BLE protocol stack, the link layer manages the state of the radio to define the role of a device as advertiser or scanner. This layer interfaces directly with the PHY layer, which uses the three advertising channels (37, 38, and 39) to transmit and receive data packets.

In this example, the standalone Stateflow chart sf_bluetooth.sfx defines the operating modes of the link layer. The chart has three states: Standby, Advertising, and Scanning. Initially, the Standby state is active, indicating that the device is idle. In the next time step, the chart transitions to the Advertising or Scanning state, depending on the value of the local data TxData. This value indicates whether there is data from the advertising bearer in the host layer available for transmission.

If there is data available, the chart transitions to the Advertising state. When this state is active, the device cycles through the three advertising channels and transmits the same data packet in each channel. The chart remains in the Advertising state for an advertising interval before it returns to the Standby state. The advertising interval is divided into three checkpoint timestamps that correspond to the three advertising channels. In this example, the advertising interval consists of a minimum of 20 milliseconds, with checkpoint timestamps at 1 millisecond (for channel 37), 9 milliseconds (for channel 38), and 17 milliseconds (for channel 39).

If there is no data available, the chart transitions to the Scanning state. When this state is active, the PHY layer passively scans one of the advertising channels for new data. If the PHY layer receives a data packet, the link layer passes it to the advertising bearer layer. The chart remains in the Scanning state for a scanning interval before it returns to the Standby state. At that point, if there is still no data available, the chart selects a new advertising channel and starts another scanning interval. In this example, the scanning interval consists of 50 milliseconds.

Simulate the BLE Link Layer

The script sf_bluetooth_demo.m creates a BLE link layer object bleLinkLayer and simulates 10 seconds of mesh communications over an advertising bearer. The link layer object relies on the standalone chart sf_bluetooth.sfx for control logic and on the link layer queue object bleQueue for storing data from the advertising bearer.

The simulation consists of 10,000 time steps. Each time step represents an execution of the link layer object (which corresponds to 1 millisecond of simulation time) and typically consists of these steps:

There are two exceptional cases:

When the simulation is complete, the script prints a summary that lists the number of data packets and bytes transmitted and received by the link layer.

Number of PDUs transmitted from link layer: 27
Number of bytes transmitted from link layer: 702
Number of PDUs received at link layer: 4
Number of bytes received at link layer: 112

During the simulation, the chart animation provides a visual indication of the runtime behavior of the algorithm. Note that chart animation slows down performance. To reduce the running time of the example, close the chart before running the script.