BLE reading notes (i)

Recently happened to do with Bluetooth this piece related development, but has been corebluetooth several agents jump to jump, the old feeling separated by a layer of yarn, just found a good book, so in learning at the same time by the way to do a few simple notes

Low power Bluetooth Development authoritative guide Read the Notes

2. Adaptive frequency hopping: a technique that uses a subset of frequencies to enable the device to avoid other non-adaptive technologies
4. Frequency hopping: Two devices use multiple frequencies to communicate with each other. At one time only one frequency is used, and each frequency is followed in a determined order
6. Bluetooth Technology Design objectives: Global operation (2.45G Hz, global free, all can be used, but the use of the frequency band technology too much, congestion, interference), low cost (no network topology design), robustness (interference prevention, adaptive frequency hopping, long CRC or Short CRC), short distance (personal LAN), Low power consumption (BLE)
8. Time is energy: a concept that runs through the entire low power consumption. Operation = Energy consumption >> reduction of execution time for necessary operations
10. Battery: Suitable temperature, too low to reduce power or even loss of battery life; Ultra-current use, exceeding the upper limit easily damage the battery (commonly known as "Battery Burn"), long-time use will also reduce the overall battery availability. When designing a device, consider the following: the battery can be restored for a period of time after a long battery operation. Battery itself leakage problem: if the battery is only occasionally used, then the battery itself leakage is an important part of the battery loss.
12. Robust discovery of other devices: reduced time required for activity >> reduced energy consumption >> extended battery life >> extended equipment use time.
14. In BLE, if a device is found north, it must send three short messages every few seconds, and if you want to find the device you intend to communicate with, the device should listen immediately after the broadcast message. When looking for another device, the device will open the receiver and listen for transmission on other devices (broadcast?)
16. The transmission of three short messages is three different frequencies, respectively >> improved robustness. The third is a balance between robustness and power dissipation.
18. Discovery equipment This work should be handed over to the energy reserve more equipment (mobile, central, peripheral, peripheral end is only responsible for performing the reception).
20. Short message short reason: Short message consumes less energy. Short messages eliminate the need for the controller to calibrate the radio continuously in a single data transfer (transmit data >> transmit energy >> chip heating >> change transmission frequency). The short message slightly reduces the chip's peak power. Short-term, intermittent power pickup is more friendly to the battery.
22. Memory needs dynamic refresh >> refresh requires energy >> more memory refresh requires more energy >> BLE design at each level consider reducing the amount of memory: The link layer maintains a shorter grouping >> less requirements for memory when sending and receiving packets in the radio ; The attribute protocol layer does not need to process any data packets with a length greater than 23 bytes; State transitions are also not required to store any state information.
24. The more things the device needs to do >> the more protocols that need to be activated >> the greater the need for storage >> BLE has only one protocol >> reduced overhead
26. Each layer of BLE uses asymmetric design >> less burden on devices for less energy
    • Physical Layer: Transmitter (peripheral) and receiver (central), a network >> asymmetric network consisting only of transmitters and a receiver-only device << all other devices must be optimized for the most resource-constrained devices
    • Link Layer: The broadcaster (peripheral) and the scanner (central), Slave devices (peripheral) and Master devices (Central), cannot initiate any complex operation from the device, the master is responsible for the timing of the Pico-NET, the adaptive frequency hopping set, Encryption and some other complex operations >> from devices can be very simple, achieving low cost, low memory and possibly low power consumption.
    • Property protocol layer: Client (Central) and server (peripheral, GATT?). The server saves the data and the client sends a data request to it to obtain the data.
    • Security architecture: An asymmetric key allocation scheme from which the device is responsible for providing the key and handing it over to the main device for storage. >> main equipment is responsible for preserving link binding information. >> implementing security features from the device is simple >> the main device is a bit of a hassle.
28. Summary: BLE, as much as possible to reduce its own overhead, all the expensive activities to move to more resource-rich equipment up.
30. Notify >> Central does not need to peripheral to perform polling, but peripheral proactively sends the value change to Central
32. The BLE state-based model (read-write-notify) builds a typical C/s architecture, while reducing the amount of code the device needs to contain and the amount of memory used to hold the code >> reduce power consumption && less code >> Less error && simpler >> less expensive >> development faster, more robust, easier to maintain less are more
34. The IP protocol is not integrated on the BLE device: memory, energy consumption does not meet the requirements >> does not allow IP packets to be routed directly to the from device >> Smart Gateway : Peripheral data storage, no need to care Central is Who, central can be connected directly or remotely via Internet gateway
36. No connection model: The basic idea of BLE is that the connection is transient (approximately 3ms can establish a connection, send data and disconnect).
37. Service-Oriented Architecture:
    • The further abstraction on the C/S is a model that organizes the information in the server into a service. The service can be interacted with by the line of defense, or used for known semantics. means that the service has deterministic behavior, and when given the same conditions, it always produces the same result.
    • Formal contracts: A service is considered a service because it provides a formal description of the features that are exposed and how they work in two ways. >> formal contracts. The advantage is that an instance of a service can easily be replaced by an instance of another service. As long as the strength of the two services has the same function and behavior, this situation is likely to occur
    • Loose coupling: Minimize dependencies to minimize the risk of unintended boundary effects when modifying the implementation of a service >> should separate formal contracts from their implementation >> as long as the formal contract is not destroyed or modified, the implementation can be arbitrarily transformed as needed.
    • Service abstraction: The state of service disclosure should be as few as possible, only the external performance of service behavior should be stipulated.
    • Reusability: The real reusability is the ability to make the service suitable for many different applications, and in good design, the service can be independent of the specific implementation process >> the service can be quickly and easily reused in other applications.
    • Stateless: The server cannot save any client's state data >> allow many clients to support service extensions. A stateless design goal is to remove all the interaction state between the client and the server, typically the server state. >> whenever any client sends any request at any time, the server will respond to the same request in exactly the same way, regardless of which client the request is from.
    • Composable: Services should be designed small and simple >> not really like this >> service-oriented architecture encourages aggregation of smaller services (a combination of services) >> implementation of more advanced service Interfaces
    • Autonomy: The service itself must be reliable >> in order to reuse and combine services >> autonomous services can perform tasks independently, regardless of what happens around them. Non-autonomous services may bring many additional support services and may conflict with other services.
    • Discoverable: If you want to use a service, you have to make the service discoverable. Discoverable is usually achieved through a separate protocol that interacts with the service. BLE uses the same protocol to implement service discovery and service Interaction >> Property Protocol >> Discoverable is called a generic attribute specification.

BLE reading notes (i)