Bluetooth v4.0 is fundamentally different from previous versions because it is based on two protocols, not a single protocol. This brings up some issues that need to be addressed by the Bluetooth Smart brand,†explains Svein-Egil Nielsen. Although the Bluetooth Technology Alliance (SIG) has been criticized for many things, it is beyond reproach to successfully establish a Bluetooth brand among consumers. An independent survey conducted in 2008 found that 85% of consumers “know wireless technology†and today the number is likely to be higher. With the launch of Bluetooth v4.0, the technology alliance faces a new challenge, which is to explain exactly what this technology is. Unlike previous versions, the Bluetooth v4.0 architecture uses two different types of radio technologies and protocols. One type can communicate with previous versions, while the other does not. From the interoperability of users' concerns to the needs of engineers, the technical alliance's answer is that new brands can help consumers find the products they need in the market. The Bluetooth v4.0 technology behind the Bluetooth Smart and Bluetooth Smart Ready brands is being widely used. The roles supported by Bluetooth 4.0 are: Broadcaster (Broadcaster) - the sender of the advertisement, not a connectable device Observer - scan ads, can't start the connection Peripheral - the sender of the advertisement, is a connectable device that acts as a slave when connected at a single link layer. Central Device - Scans the ad to initiate a connection and acts as a host when connecting at the single or multi-link layer, supporting three simultaneous connections The broadcaster can't establish a connection by pairing with the observer. Application: Temperature sensor and temperature display. The central device and peripheral devices can be connected, paired, and communicated with each other. Application: Watch and mobile phone. The process of BLE connection: 1. The peripheral device sends specific advertisement data to let any central device know that it is a connectable device. The advertisement content includes the device address, and may also include some additional amount of data, such as device name, service ID, and the like. 2. After receiving the advertisement, the central device sends a search request to the peripheral device (Peripheral), and the peripheral device (Peripheral) returns the scan response to the central device (Center). This way the central device knows that this is a connectable device. 3. The central device can send a request to establish a connection to the peripheral device. Make a paired connection and bind as necessary (the connection can be terminated by either the slave or the host). Pairing: Establish a connection, and data communication can be performed after pairing is completed. Banding: Record the pairing information, such as the device address, so that the next time you connect, you don't need to pair again (quick connection). Bluetooth low power: The low-power Bluetooth technology uses only 3 channels for the broadcast channel, allowing the connection to be established quickly in milliseconds, which is much more efficient than the 32 channels of traditional Bluetooth. Less data channels and wide channel spacing: Traditional Bluetooth has 79 data channels with a channel spacing of 1 MHz; low energy Bluetooth has 40 data channels with a channel spacing of 2 MHz. The traditional Bluetooth peak current is typically 35mA, and the sleep state current is 0.01mA. The low-energy Bluetooth operating peak current is less than 15mA, and the sleep state current is 0.004mA. Connection interval: When the device establishes a connection, even if there is no data transmission and reception, the two devices still maintain the connection by exchanging link layer data, which is the time interval between two connection events. Setting range (7.5ms - 4s). Slave Delay: The slave can skip several connection events and continue to sleep to save power. Management timeout: The maximum allowable interval between two successful connection events. If this time is exceeded, the device is considered to be disconnected. Setting range (100ms--32s) The protocol defines a series of communication standards, and both parties need to jointly perform normal data transmission and reception according to this standard. The protocol stack is a concrete implementation form of the protocol, which is generally understood as a function library implemented by code, so that developers can call it. The Bluetooth 4.0 BLE protocol stack combines the protocols defined by each layer, implements them in the form of functions, and provides some application layer APIs for users to call. Note: Although the protocol is unified, the specific implementation form of the protocol is different, that is, the protocol stack provided by different vendors is different. For example, the function name and the parameter list may be different. After selecting the protocol stack, you need to learn the specific For example, look at the Demo demo program and documentation provided by the vendor (usually, the vendor that implements the protocol stack will provide some API manuals for users to query) to learn how to use each function, and then quickly use the protocol stack to develop the application. Since the Bluetooth 4.0BLE protocol stack has implemented the Bluetooth 4.0 BLE protocol, the user can use the API provided by the protocol stack to develop the application. In the development process, it is not necessary to pay too much attention to the specific implementation details of the Bluetooth 4.0 BLE protocol. Focus on a core question: Where does the application data come from? As for the function of calling the protocol stack, how to initialize the application for data transmission, etc., the Bluetooth 4.0BLE protocol stack has completed the required initialization. If you really need or want to understand the Bluetooth 4.0 BLE protocol during development, you can check out the standard protocol specifications provided by the SIG. We take TI's CC254X series BLE chip as an example to gain an in-depth understanding of the Bluetooth 4.0BLE protocol stack. TI's Bluetooth 4.0BLE protocol stack consists of two parts: the host and the controller. The separation of the host and controller goes back to the Bluetooth BR/EDR device period, and the controller and host are usually implemented separately. The implementation of the protocol stack adopts a layered idea. The controller part includes: a physical layer, a link layer, and a host control interface layer; the host part includes: a logical link control and an adaptive protocol layer, a security management layer, an attribute protocol layer, Universal access profile layer, common property profile layer; upper layer can call the functions provided by the lower layer to achieve the required functions.
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