高精度PCI授时板卡的设计与实现

Design and implementation of high-precision timing board based on PCI

针对普通计算机自身时间频率稳定性较差、准确度较低的问题,提出一种利用外部硬件授时板卡同步计算机时间的设计方案。首先,将国际通用的美国靶场仪器组B型时间码(IRIG-B)或全球定位系统(GPS)信号接收机输出的时间信息作为参考时钟源来同步授时板卡的本地时钟;其次,利用参考时钟源准时秒脉冲和板卡上晶振频率在时间误差上互补的特点,对多个连续秒脉冲间的晶振计数脉冲计数值进行动态平均,周期性求取晶振的实际频率;最后,利用分频模块结合晶振实际频率产生1 k Hz的外设部件互连(PCI)总线中断信号来将计算机时间同步到毫秒级。实际测试结果表明,当外部参考时钟源有效时,授时板卡本地时钟授时误差约为250 ns,利用晶振实际频率产生的PCI中断信号频率误差比直接利用晶振标称频率产生的PCI中断信号频率误差小40 Hz以上;当外部参考时钟源失效时,利用晶振实际频率产生的本地时钟自守时误差比利用晶振标称频率产生的本地时钟自守时误差小约20μs/min。利用晶振实际频率的设计方案相比直接利用晶振标称频率的设计方案能够有效减小计算机时间同步误差。

Time of a normal computer often has poor frequency stability and low accuracy. To solve this problem, a computer time synchronization scheme using external hardware timing board was proposed. First of all, the local clock on timing board was synchronized by the IRIG-B serial time code which is internationally used or time information from Global Positioning System（ GPS） receiver, which is treated as the reference clock source. Second, the real frequency of the crystal on timing board could be calculated periodly by making dynamic average on the crystal＇s pulse counts between several continuous Pulse Per Second（ PPS）, based on the complementary characteristics of their time errors. Last, the computer time was synchronized to millisecond level by Peripheral Component Interconnection（ PCI） interrupt signal with the frequency of 1 kHz,which was generated by frequency division module with the real frequency of the crystal. Actual experiment results show, when the external reference clock source is valid, the timing error of local clock on timing board is about 250 ns, and the frequency error of PCI interrupt signal generated by using the real frequency of the crystal is less above 40 Hz than that generated by directly using the nominal frequency of the crystal; when an external reference clock source is invalid, the local clock＇s holdover error generated by using the real frequency of the crystal is less about 20 μs/min than that generated by directly using the nominal frequency of the crystal. The design scheme using the real frequency of the crystal can effectively reduce the computer＇s time synchronization error compared to that directly using the nominal frequency of the crystal.