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1、光收发模块DDM功能介绍,-夏致富 QQ:706336149 手机：,一、DDM定义,DDM(数字诊断监视功能)means digital diagnostic monitoring,definein SFF-8472 documents.监测的5个实时测量参数为：模块温度temp 工作电压Vcc 激光器偏流Laser Bias 接收光功率Rx_power 发射光功率Tx_power,1、DDM的实现流程,读取 5个监控量参数经过A/D转换，将模拟量转换为数字量。通过内部校准或外部校准，将监测的校准值或外部校准系数写入内存中(E2ROM)。,2、DDM功能的应用,通信的一个重要指标就是要保证通
2、信数据传输正确，也就是不能产生误码，在产生误码的情况下就要重新建立数据链接。但是模块在使用的过程中会出现其他因素影响模块的功能使得通信数据出现错误，比如：模块的使用温度、光纤的曲折影响光功率、模块本身的使用寿命。传输者不能把有误码的数据也传送给接收者，同样做为接收信号的一方也不能把有误码的信号拿来使用。这样就需要知道模块当前的运行状况，以使模块在正常的工作条件下传输数据。于是就需要连续（间隔一定时间）的监视模块当前的状况，也就是监测上面所说的5个指标。然后将监测到的值对比模块在正常工作条件下所要求的范围。如果不在范围之类就报警，显示模块处在不良状况下，交换机就会停止发送数据，同样作为接收信息一
3、方拒绝接收数据。直到模块正常工作状况下重新发送/接收数据。同时,如果光网络数据链路出现问题,可以帮助系统管理员找出光纤链路中发生故障的位置，简化维护工作，提高系统的可靠性。,模块使用时间预测智能带DDM的SFP提供了一种预测激光器劣化的实时的参数监测手段。光模块内部的光功率反馈控制单元会将输出功率控制在一个稳定的水平上，但是，随着激光器的老化，激光器的量子效率会降低。功率的控制是通过提高激光的偏置电流（Tx_Bias）来实现的。因此，我们可以通过监测激光的偏置电流来预测激光器的寿命。这种方法可粗略的估计激光器的使用寿命是否接近终了。因为激光的偏置电流与模块的工作温度及工作电压都有关系，所以在设
4、定偏置电流极限时需要考虑Temp和Vcc的影响。通过对收发模块内部的工作电压和温度进行实时监测，可以让系统管理员发现一些潜在的问题：1）Vcc电压过高，会带来CMOS器件的击穿；Vcc电压过低，激光器不能正常工作。2）接收功率太高，会损坏接收模块。3）工作温度太高，会加速器件的老化。此外，通过对接收到的光功率的监测，可以对线路和远端发射机的性能进行监控。这种故障预测可以使网络管理人员在系统性能受到影响之前找到潜在的链路故障。通过故障预告，系统管理员可以将业务切换到备份链路上或者替换可疑器件，从而在不间断业务的情况下修复系统。,故障定位在光链路中，定位故障的发生位置对业务的快速加载至关重要。故障
5、隔离特性则可以使系统管理员快速定位链路故障的位置。此特性可以定位故障是在模块内还是在线路上；是在本地模块还是在远端模块。通过快速定位故障，减少了系统的故障修复时间。故障定位中，需要综合分析状态位，管脚和测量参数。总之，通过数字诊断功能，可以定位故障。在故障定位中，需要对Tx_power，Rx_power，Temp，Vcc，Tx_Bias的警告和告警状态进行综合分析。内存镜像中的状态变量Tx Fault和Rx LOS(信号丢失)都对故障的分析起着重要的作用。,兼容性验证数字诊断的另一个功能是模块的兼容性验证。兼容性验证就是分析模块的工作环境是否符合数据手册或和相关的标准兼容。模块的性能只有在这种
6、兼容的工作环境下才能得到保证。在有些情况下，由于环境参数超出数据手册或相关的标准，将造成模块性能下降，从而出现传输误码。工作环境与模块不兼容的情况有：1）电压超出规定范围；2）接收光功率过载或低于接收机灵敏度；3）温度超出工作温度范围。,3、DDM-SFF-8472,在SFF-8472 MSA中，规范了数字诊断功能及有关SFF-8472的详细内容。该规范规定，在模块内部的电路板上监测和数字化参数信号。然后，提供经过标定的结果或提供数字化的测量结果及标定参量。这些信息被存贮在标准的内存结构中，以便通过两线串行接口读取。SFF-8472保留了原来SFP/GBIC在地址A0h处的地址映射，并在地址A
7、2h处又新增了一个256字节的存贮单元。这个存贮单元除了提供参数监测信息外，还定义了报警标志或告警条件，各个管脚的状态镜像，有限的数字控制能力和用户可写的存储单元。The enhanced interface uses the two wire serial bus address 1010001X(A2h)to provide diagnostic information about the modules present operating conditions.The transceiver generates this diagnostic data by digitization o
8、f internal analog signals.Calibration and alarm/warning threshold data is written during device manufacture.,Digital Diagnostic Memory Map Specific Data Field Descriptions,Diagnostics:Data Fields Address A2h,二、DDM功能,Diagnostics Overview Address A2h 2 wire serial bus address 1010001X(A2h)is used to a
9、ccess measurements of transceiver temperature,internally measured supply voltage,TX bias current,TX output power,received optical power,and two additional quantities to be defined in the future.The values are interpreted differently depending upon the option bits set at address 92.If bit 5“internall
10、y calibrated”is set,the values are calibrated absolute measurements,which should be interpreted according to the section“Internal Calibration”below.If bit 4“externally calibrated”is set,the values are A/D counts,which are converted into real units per the subsequent section titled“External Calibrati
11、on”.,Measured parameters are reported in 16 bit data fields,i.e.,two concatenated bytes.The 16 bit data fields allow for wide dynamic range.This is not intended to imply that a 16 bit A/D system is recommended or required in order to achieve the accuracy goals stated below.The width of the data fiel
12、d should not be taken to imply a given level of precision.It is conceivable that the accuracy goals herein can be achieved by a system having less than 16 bits of resolution.It is recommended that any low-order data bits beyond the systems specified accuracy be fixed at zero.Overall system accuracy
13、and precision will be vendor dependent.To guarantee coherency of the diagnostic monitoring data,the host is required to retrieve any multi-byte fields from the diagnostic monitoring data structure(IE:Rx Power MSB-byte 104 in A2h,Rx Power LSB-byte 105 in A2h)by the use of a single two-byte read seque
14、nce across the two-wire interface.,The transceiver is required to ensure that any multi-byte fields which are updated with diagnostic monitoring data(e.g.Rx Power MSB-byte 104 in A2h,Rx Power LSB-byte 105 in A2h)must have this update done in a fashion which guarantees coherency and consistency of th
15、e data.In other words,the update of a multi-byte field by the transceiver must not occur such that a partially updated multi-byte field can be transferred to the host.Also,the transceiver shall not update a multi-byte field within the structure during the transfer of that multi-byte field to the hos
16、t,such that partially updated data would be transferred to the host.Accuracy requirements specified below shall apply to the operating signal range specified in the relevant standard.The manufacturers specification should be consulted for more detail on the conditions under which the accuracy requir
17、ements are met.,Internal Calibration Measurements are calibrated over vendor specified operating temperature and voltage and should be interpreted as defined below.Alarm and warning threshold values should be interpreted in the same manner as real time 16 bit data.Converted analog values.Calibrated
18、16 bit data.,External Calibration Measurements are raw A/D values and must be converted to real world units using calibration constants stored in EEPROM locations 56 95 at 2 wire serial bus address A2h.Calibration is valid over vendor specified operating temperature and voltage.Alarm and warning thr
19、eshold values should be interpreted in the same manner as real time 16 bit data.,Alarm and Warning Flags Address A2h,Bytes 112-117 Bytes 112 117 contain an optional set of alarm and warning flags.The flags may be latched or non-latched.Implementation is vendor specific,and the vendors specification
20、sheet should be consulted for details.It is recommended that in either case,detection of an asserted flag bit should be verified by a second read of the flag at least 100ms later.For users who do not wish to set their own threshold values or read the values in locations 0-55,the flags alone can be m
21、onitored.Two flag types are defined.,Alarm and Warning Thresholds,Alarm and Warning Flag Bits,continuation：,三、DS1859实现DDM功能,The DS1859 dual,temperature-controlled,nonvolatile(NV)variable resistors with three monitors consists oftwo 50k or two 20k,256-position,linear,variableresistors;three analog mo
22、nitor inputs(MON1,MON2,MON3);and a direct-to-digital temperature sensor.Thedevice provides an ideal method for setting and temperature-compensating bias voltages and currents incontrol applications using minimal circuitry.The variableresistor settings are stored in EEPROM memoryand can be accessed o
23、ver the 2-wire serial bus.,Memory Organization,ADEN=1,If the ADEN bit is 1,additional 128 bytes of EEPROMare accessible through the Main Device,selected asTable 00(see Figure 3).In this configuration,theAuxiliary Device is not accessible.APEN controls theprotection of Table 00 regardless of ADENs se
24、tting.ADFIX(address fixed)determines whether the MainDevice address is determined by an EEPROM byte(Table 01,byte 8Ch,when ADFIX=1).There can beup to 128 devices sharing a common 2-wire bus,witheach device having its own unique device address.,四、常见问题分析,（一）客户对DDM的查看1、客户主要是通过交换机来查看模块是否具有DDM功能和监控量。比如需要
25、查看在H3C交换机的模块是否具有DDM功能，在超级终端输入命令：display tran int gig 1/1/X；查看DDM监控量，在超级终端输入命令：dis tran diagnosis int gig 1/1/X。2、可以通过读码查看是否带DDM功能，读取A0中92位字节数据第6位，如果置1说明模块带DDM功能，否则不带DDM功能。,（二）DDM的测出的数据是否准确.,每次测试前必须校准VCC电压为.,前面讲到，Vcc电压过高，会带来CMOS器件的击穿；Vcc电压过低，激光器不能正常工作。输入电压的不准确势必影响其他参数，而在我们的测试中有一项自动调电阻来调节光功率在基准参数都不对的情况下是无法测出准确的结果的,Thank you for your participation!,
