ARM9-based CAN-bus converter card 1553B and Design and Implementation
The birth of the 20th century 70's 1553B bus is a master-slave bus, the bus more than the hardware redundancy, there are strict requirements, reliability and real time and transfer rate up to 1 Mb / s, for most applications can meet Through decades of development, has become the first choice of military electronic bus. BOSCH, Germany, developed by the CAN bus, multi master mode, the maximum rate of 1 Mb / s, because of its electronic systems in automotive excellence, and now more and more users by the attention and recognition. The two bus transfer rates are high, high reliability and good real-time performance bus, but they all have some shortcomings. 1553B data bus at any time an order by the master node since the node receiving the order from the analysis and implementation, while the corresponding state feedback to the master node, which makes network data transfer rate was greatly decreased and to the master node controller is very busy, and abnormal in the bottom, the data can not immediately upload, the master node must wait for the transmission command, poor flexibility. The CAN bus to compete in multi-master bus, can better solve the problem. However, there are many shortcomings CAN bus, for example, and the 1553B bus as he was unable to give a more defined response time, and no dual redundant or redundant structural design, which makes him the reliability and timeliness as 1553B, and in military electronics, the reliability and timeliness are the most important. Therefore, military electronic systems, 1553B bus has been widely used, but the hardware cost is very high 1553B bus, CAN bus, under the same conditions is hundreds of times, it is difficult for the test system to bear, so in the present control system still used for the control of 1553B bus, CAN bus used for the test, and information exchange between the two became the key to the whole system to promote the conversion of the 1553B and CAN bus card design and implementation.
2 design
1553B bus frame structure 2, in fact, the command word and status word share a frame structure. This synchronization is only the first two frames are different
1553B of the frame and started three for the synchronous bit data word is on the jump along, and the command word and status word for the falling edge, 4 to 19 for the data bit, data word for transmission of data, command and status word for the command or status word bits, the last one for the parity bit. In the CAN bus, only one kind of frame structure, is only whether to adopt the extended frame only, the frame structure shown in Figure 2.
ARM9-based CAN-bus converter card 1553B and Design and Implementation
Frame in which the start was bit by a single component, the arbitration field formed by the identifier and the RTR bit, a total of 12, the control field from the two reserved bits and 4 bits of DLC, the data field from 0 to 8 characters, each 8-bit characters, CRC field 15-bit CRC sequence and an identification bits, ACK ACK field from the one gap and one ACK delimiter composed of the end of the last frame hidden by a row of 7 bits.
Thus, 1553B and CAN bus frame structure is not only different, not the same as the command system, and different between the 1553B and CAN bus conversion method is not the same, so the 1553B and the conversion between the CAN bus is not just the frame structure conversion, but also to resolve the order between the two systems, so using the software more flexible ways to achieve these two bus conversion.
The need to achieve the conversion and 1553B in the CAN bus to be built between the endpoint and a reasonable schedule to run multiple applications platform. Comprehensive consideration of the conversion board using the ARM9 processor with the operating system to achieve this platform is more appropriate. cAN bus parts, can be designed as a general master node, while the 1553B bus parts, as 1553B with 3 different endpoints, in order to extend the functions of conversion board, can change the design board of the endpoint can be achieved by different configurations different functions, so this requires the agreement 1553B and the upper endpoint applications can be configured, for FPGA and ARM can be used to work a way to achieve this endpoint. In order to achieve real-time monitoring, can extend from the ARM9 serial ports and LCD interfaces on to achieve.
3 Design and Implementation of conversion card
3.1 Transformation of the choice of hardware cards
Adapter card hardware is the conversion function based on its implementation block diagram shown in Figure 3. Conversion card in the hardware design, the device determines the choice of the actual programs and circuit design. For the CAN node, using PHILIPS company SJA1000T CAN bus controller and TJA1050CAN bus transceiver to the common realization. For 1553B nodes, some functions of the FPGA to achieve agreement with ALTERA's EP1C3T144, transceiver and transformer used HOLT's HI-1567 and PD2725, they completed together with the ARM9 agreement 1553B endpoint. The core processor is finally with ATMEL ARM9's AT91RM9200T, he has a 180 MHz frequency, 4 PIO interface, not only with the FPGA have completed 1553B endpoint functions to meet the requirements for real time 1553B, but also the operating system needed for the operation and applications, to complete the transformation. For real-time monitoring is used, LCD chips using the S1D13506 EPSON expansion chip, and serial port is using the traditional MAX3232. These chips form more than the adapter framework, they constitute a transformation through the card's hardware.
In this scenario, RAM with a dual-port RAM, 1553B and ARM9 share a port, so out of CAN bus data and 1553B data bus, do not turn over the deposit can be output directly or through another section of the buffer waiting to send. S1D13506 chip is a multi-chip extension, he still has many extensions, can extend the audio and video interface.
ARM9-based CAN-bus converter card 1553B and Design and Implementation
3.2 conversion card software implementations
Conversion card in the whole implementation is the biggest problem facing the real-time conversion and buffer data management, this adapter is very good through the use of real-time preemptive multitasking operating system RTLinux to resolve. He not only can meet real time demands of the system on completion of the bus on both sides of the buffer data management, but also for the application and conversion to provide a good operating environment. Conversion process was completed for two functions: the 1553B bus to the CAN bus data into the frame structure, or vice versa; the 1553B bus to the command parsing, CAN bus system into the command and send the frame structure composed of CAN. Conversion card to provide users with MiniGUI real-time monitoring of the graphical interface, this graphics card interface can be extended by converting a good LCD to complete the process of information exchange real-time monitoring task. Finally, the ARM9 ARM9 JTAG port can run applications and conversion program to modify and debug.
3.3 conversion card conversion mechanism
Design by interrupt priority control mechanism, a different set different interrupt source interrupt levels to meet the requirements of real-time systems. This mechanism is mainly based on the following considerations:
(1) from the 1553B, CAN, and serial port hardware interrupt request signal and from the application of soft interrupt signal is random. ARM9 interrupt mechanism to allow real-time response to each interrupt, and make the appropriate action. Real-time requirements are relatively high 1553B endpoint is given high priority interrupt can be deprived of CAN, serial and other relatively low-priority interrupt service. The CAN was given the second highest priority, applications, and serial port is assigned the lowest priority.
(2) 1553B and CAN data transmission rate is different. CAN bus of different configurations, 1553B bus controller will cause the different scheduling 1553B and CAN bus data transfer rate of change CAN be faster than 1553B, 1553B may also be faster than CAN. An interrupt can significantly reduce the slow handling of the more high-speed equipment delay.
While taking into account the design of hardware and software is flexible, so all interrupt signals are designed to be by check.
3.4 Hardware Test
The hardware is complete, the entire hardware tested. First of all endpoints connected in 1553B to 1553B bus system, he can properly respond to the bus, through the oscilloscope to observe the transformer and the transceiver and the signal transformation sequence, the sequence of the signal level and are in line with the established requirements. Then write the FPGA and the 1553B protocol endpoint ARM, the endpoint of the reaction time test, that receives commands sent word to the interval between the status word, this time between 1.5 ~ 2.5μs, fully meet the requirements 1553B bus protocol. Finally the CAN bus, serial port, LCD interfaces are connected, the hardware works well.
4 conversion card functions and features
4.1 The main function of conversion card
(1) conversion card in a given agreement can be achieved under the CAN bus system and the 1553B bus system information exchange, while the two-bus system to meet real time requirements.
(2) conversion card can be a CAN bus node or endpoint connected to the 1553B bus, the bus system, the completion of the corresponding node function.
(3) to achieve on-site debugging and monitoring. Application conversion card expansion port and serial LCD, LCD screen or the user can monitor and control the external computer of information between the two bus conversion.
4.2 Hardware Features
(1) 1553B end-point agreement with the ARM chip, using a common FPGA implementation, this design not only by changing the protocol procedure to configure the remote endpoint endpoints, controls, monitors and other 3 different functional endpoints, but also because through the ARM9 and FPGA realization of a common bus protocol, so when, after receiving complete 1553B bus data conversion process can trigger bus, thus reducing a separate agreement with 1553B chip data on the ARM9 interrupt request time, the control system to better meet the real time requirement. Finally this design and direct purchase agreements 1553B chip endpoint significantly reduced compared to the cost of hardware conducive to the promotion and application of 1553B bus.
(2) can be compatible with different rates of CAN bus, by changing the configuration initialization can achieve different rates of CAN bus communication with the 1553B bus system. Implemented on the ARM9 conversion card storage expansion, by extending the 16 MB FLASH and 32 MB RAM, so when the bus data transfer rate on both sides does not match, you can wait for data sent into the special opening of the buffer storage, waiting for the bus idle and then sent, although the fastest transmission speed CAN bus, the same with the 1553B, but since 1553B is a master-slave bus, each node can only transmit in one cycle a certain amount of data, so his data transfer rate may also slower than the CAN bus, so the data buffer is twofold.
(3) extension of the LCD interface and serial port. In the field through the 40-pin interface, or the upper LCD Computer Monitor information exchange between the two buses, but also through the serial port and the JTAG port in real time ARM9 ARM9 debugging the program.
(4) Good real-time. In the interface, and the 1553B bus through CAN interrupt response priority setting, can be very good to meet the system requirements for real-time nature.
5 Concluding Remarks
The practical application shows that, based on ARM9-1553B and CAN-bus converter card, whether hardware or software Du can satisfy 1553B and CAN 总线 right 实时, reliability and speed requirements, in a certain Mingling system could achieve CAN and the conversion of information between the 1553B bus.