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| System of Loongson 2F vehicle-mounted and portable equipment |
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In recent years, vehicle-mounted and portable multimedia devices are sought-after by people, raced to offer a variety of designs. The Godson 2F-based[1,2] (LOONGSON-2F) processor board and portable devices design proposal is primarily for car entertainment solutions, ultra mobile devices (UMD), mobile Internet devices (MID) and other companies engaged in the development and production of the fields of high-performance, low-power embedded type . The program uses Godson-2F (LOONGSON-2F) processor for controlling core, according to work environment and characteristics of the vehicle-mounted and portable devices, using the SM502 [3] multi-function display control chip, which can support a variety of media formats, enabling to surf the Internet, see television, music recording and playback music and so on functions; on-board FLASH and DDR2 memory, independently boot the system kernel to work, using the serial port as a system terminal. Can also use the common PCI and LOCAL BUS head route interface to do system expansion, be convenient for users to do secondary development, combined with the domestic chip for CPU with the characteristics of low power consumption, low-cost , the design has a high application and reference value. 1. The functions and characteristics of Loongson 2F processor The system uses a Godson 2F (LOONGSON-2F) processor, which is a 64-bit MIPS Ⅲ instruction set common RISC microprocessor latest issued by Chinese Academy of sciences computing technique Institute. The processor is the first to use 90nmCMOS design technology interiorly, an area of 35nm2, typical operating frequency of 800MHz, actual measurement power consumption of 4 "5W , the maximum operating frequency of up to 1G; the highest floating-point operations speed of per second 40/80 billion double / single-precision floating-point operations per second, on-chip integrated PCI / PCIX IO controller, etc., and integrated on-chip L2 CACHE, DDR2 memory controller, is very suit for the high-end embedded domain. 2. Structural design of system hardware Godson-2F (LOONGSON-2F) processor is the control center for the entire system, and undertake all tasks of data processing. System generated clock required every chip in the motherboard by the ICS950220 clock synthesizer, while the chip is with a watchdog function. System memory is expended through the processor interior integrated DDR2 controller, taking into account the size of PCB and the higher bandwidth requirements, using four 16bit-bit internal storage particle program, memory capacity depends on the particle capacity ,maximum 1GB memory, the operating frequency is 300MHz. By LOCAL BUS provided by the processor extend 512KB Flash ROM for system BIOS storage. 3. System software The system runs on the operating system of LINUX DEBIAN4.0, the kernel is LINUX 2.6.21. Bootloarder-PMON2000 is fired on the on-board BIOS ROM, after power up automatically finish initialization for the processor, cache, memory controller, network controller. Also PMON2000 has a few line command set , after starting for using for memory read and write parity, Flash-erase board, IP settings, serial settings, and data communication with the host, including upload, transfer files under the receiver Host directed and so on. By PMON2000 internal command ,put LINUX 2.6.21 kernel into memory. In memory, there is a ROM, which holds the memory size, number of row address, column addresses, memory bank number and other information that can be accessed via the I2C bus. As a general design, it requires to support a variety of different types of memory. In the process of the system debugging, we found SM502 chip I2C logic has a bug. Therefore, to use of gpio of SM502 to imitate I2C timing, and achieve information read for the memory bank(DIMM). And use the read information to do configuration for DDR2 control of 2F Godson processors, and receive a good result. After testing, the system currently support all types of memory in the market . 4. Design of signal integrity Since the whole system module circuit is small, operating frequency of the circuit is high, so there are strict requirements for signal integrity of the whole design . Operating frequency of general line for 2F Godson processor DDR2 memory is up to 300MHz, this part of the circuit is a bottleneck in high-speed circuit design, simulation result for this part of the circuit can basically reflect the effect of the whole circuit signal transmission. Following the DDR2 control signals, for example, describe the design methods and processes for this problem. In practical design, firstly use Godson 2F IBIS models and simulation tools [4] predefine the topology structure and matching method of the key signal, from this to formulate PCB layout constraints. Firstly picking up simulation model before PCB layout , by observing the corresponding simulation results waveform, to obtain circuit topology structure and matching circuit parameters of better signal quality. After completing PCB layout, and then extract the actual topology to do simulation, the topology after extracting. At this point the model has been included the PCB stackup and impedance control information, and model the actual hole. To obtaining the best alignment by adjusting alignment and observing simulation results. Figure 4 shows the simulation results after adjusting, it can be observed to obtain a better signal quality at the receiver side, and the overshoot phenomenon at driver side is also within the acceptable range. Finally, in the actual board-level debugging re-measure the actual signal waveform, by adjusting the matching components to ensure reliability of the actual signal quality. Practice shows that, based on this approach and process to reduce the risk of signal integrity and reduce debugging difficult that brought from the design. All simulation IC modeling parameters shown in this draft are typical, pumping signal of driver is the 133MHz signal. 5. Conclusion This article describes design process of 2F Godson-based processors vehicle and portable equipment system , the main is the system hardware structure, software systems, signal integrity design, improving machine efficiency and other key technologies . The system has a compact system to work both independently and provides a flexible expansion interface, has great application prospect. |
