Introduction of 1arinc659 bus
The Arinc659 bus topology is shown in Figure 1. In avionics system, data communication between LRM modules is realized through Arinc659 backplane bus. Each LRM module contains two bus interface units BIU (biux, biuy), and each BIU has two bus pairs a and B. each bus pair contains two buses “X” and “Y”, namely ax, ay, BX and by4 buses. Each bus has a single clock line and two data lines, and can transmit two data bits in each clock cycle. Biux and biuy send data on their respective buses, and each BIU can receive data on four buses. Each bus has its own transceiver. Arinc659 bus data is used for error detection and fault tolerance through cross check. The detection rules are AX = ay, BX = by, ax = by and BX = ay. Compared with the traditional dual redundancy bus, Arinc659 bus has better fault tolerance and less complexity.
LRM module is generally composed of host computer and bus interface unit. According to its structure, it can be divided into host computer circuit and backplane bus interface unit circuit, and these two circuits can be integrated into the same circuit board to form LRM module at the same time. It can also be interconnected with host computer sub card by a separate Arinc659 bus interface sub card to form LRM module.
1.2 system working principle
The working mechanism of Arinc659 bus is TDPA communication mechanism driven by command table. The command table is shown in Table 1. The host on each LRM module accesses its BIU, and the host interface controls the BIU module. The BIU operation commands are written in the form of command table by compiling software. Before the LRM module executes the corresponding command, it is necessary to allocate the storage space of the received data. After the system is powered on, the BIU of each LRM module starts to read the command list, parse the commands to be executed, and carry out bus data transmission and synchronization pulse according to the preset content format of the command list. According to the command table format, BIU can send the stored data to Arinc659 bus, or send the data received on the bus to the host through the host interface; when it sends and receives the synchronous pulse, it can switch and maintain the synchronous state between modules by sending or receiving the synchronous pulse on the bus.
In Arinc659 bus system, synchronization is the premise and key to realize TDPA protocol. In order to realize the synchronization of each BIU on Arinc659 bus, the synchronization mode includes long synchronization and short synchronization. Among them, “long synchronization” is used to synchronize the out of synchronization BIU with the bus again, “short synchronization” is used to make the synchronized BIU correct the drift of its clock oscillator and make all BIUs on the bus reach the tight synchronization state; “long synchronization” can be divided into three types according to its function “Initialization synchronization” and “entry synchronization”, in which the initialization synchronization is to initialize the bus when the system is powered on or the whole bus is out of step due to “fault”; the entry synchronization can synchronize the non synchronous LRM module to the current frame.
Arinc659 bus data transmission includes basic message and main / backup message.
(1) The data flow diagram of point-to-point transmission of basic message is shown in Figure 2. Basic message is used for communication between modules (point-to-point) or from single module to multi module, and basic message transmits data at the beginning of window.
(2) The data flow diagram of broadcast transmission of basic message is shown in Fig. 3.
(3) There are two kinds of data flows for primary and backup message transmission: ① as shown in Figure 4, the primary module sends the primary and backup messages normally. The primary / backup messages are used for communication between multiple backup modules (no more than 4) and single or multiple modules. The primary / backup messages are transmitted by simple arbitration mechanism, and only when the primary LRM and other high priority backup LRMS are pre specified in the command table The backup LRM module starts to send data to the bus only when it does not send data within a certain period of time, and in a message window, Arinc659 bus only allows one LRM module to send data; ② as shown in Figure 5, the main module sending abnormal sending of the main backup message.
1.3 technical features and advantages
Arinc659 bus is a kind of multi-channel serial communication bus, which is used for data transmission between frame integrated modular avionics systems (IMA). The transmission mode adopts half duplex data transmission, and the data verification adopts the error correction mechanism of cross check, which is executed according to the predetermined table command (bus operation schedule). It has two independent BIU control modules and four bus coding modes respectively . Arinc659 bus has the characteristics of strong division in bus transmission time and storage space. It is a high fault tolerance, high integrity backplane bus, and a serial bus with strong fault tolerance and high reliability. It meets the technical requirements of the system for high reliability, high fault tolerance and high fault tolerance of backplane bus.
Arinc659 bus has the following characteristics and advantages:
(1) High reliability: due to the redundancy mechanism of the bus, four buses carry out the same data transmission, which makes Arinc659 bus highly reliable. Its data transmission is coded and then transmitted according to different coding rules. The coding rules are shown in Table 2. The reliability of the system is improved through the main backup mode of LRM module. At the same time, in Arinc659 protocol, through a series of isolation mechanisms, the reliability of the system is also increased in the physical layer.
LRM redundancy means that the LRM module sends data to the bus from the module with the highest priority according to the preset priority, while the module with lower priority keeps silent. Only when the main LRM and the LRM with higher priority keep silent, can they send data to the bus.
(2) Strong fault tolerance: Arinc659 bus uses four dual dual backup serial buses to transmit data, and its strong fault tolerance is better than the traditional dual dual redundancy bus, and its complexity is less than the traditional four redundancy bus;
(3) Certainty of data transmission: in the traditional backplane bus system, the bus must be applied before data transmission, which can not guarantee the real-time performance of data transmission. Arinc659 bus uses TDPA communication mechanism, and TDPA protocol stipulates that the bus command table format should be defined first, the bus transmission window should be set in advance, and the bus time should be divided into a series of windows of fixed length, which is very important The host only needs to organize the sending in a fixed time window. At the same time, the host only needs to send data in accordance with the rules in a fixed time window and query the data update flag at a fixed time point to complete the data receiving;
(4) Medium / high data throughput: the clock is 30MHz, and the maximum data transmission rate is close to 60MB / s;
(5) It has strict fault isolation and error correction ability. The LRM module sends data to and receives data from the bus according to the command. During this period, the fault detection is carried out according to the data verification rules. The LRM module compares and corrects the data received on the four buses, and the data that cannot be corrected should be processed according to the rules in the corresponding message description;
(6) Efficient bus utilization: according to TDPA protocol, Arinc659 backplane bus can avoid the transmission of start, end, error check and other characters on the traditional serial bus, reduce the bus bandwidth occupied by non data information character transmission, and eliminate the possibility of transmission address error. Compared with Arinc659 backplane bus, Arinc659 backplane bus can transmit more easily More effective data and higher bus utilization.
Application of 2-bus
Arinc659 backplane bus is widely used in the aircraft information management system (AIMS) of Boeing 777 and the avionics (via) of Boeing 717. It provides a standard backplane bus for the data transmission between the integrated modular electronic rack LRMS in the follow-up avionics subsystem.
Arinc659 bus is widely used in aerospace and other fields because of its high reliability, simple and flexible use. Based on the background of Arinc659 bus, this paper analyzes the topology, working principle and characteristics of Arinc659 bus, and studies Arinc659 bus, which has important reference value for subsequent Arinc659 bus protocol research, chip development, application solution and system design of Arinc659 bus.
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