[FPGA]: IP core ibert

Reference material ：
【1】FPGA—7 Series of IBERT_GTX Inner and outer ring test
【2】 utilize IBERT Conduct GTX Signal eye diagram test
【3】 How do you use it? IBERT？
【4】ibert Test instructions

One 、 summary

IBERT（ Integrated bit error rate tester ） yes xilinx by 7 series FPGA GTX Transceiver design , For evaluation and monitoring GTX Transceiver .IBERT Included in FPGA Pattern generators and checkers implemented in logic , And access to ports and GTX Dynamic reconfiguration of the transceiver port properties , It also includes communication logic , To allow the design to pass at runtime JTAG Visit .

IBERT Tools are used to Xilinx FPGA The high-speed serial transceiver of the chip is tested at the board level . adopt IBERT Bit error rate can be obtained , Look at the eye chart , Adjust the parameters of the serial transceiver , It helps to judge the possible problems , It is convenient to verify the stability and signal integrity of the hardware .

Two 、 Test principle

GTX The receiving and sending directions are determined by PMA and PCS Two parts ,PCS Provide rich physical coding layer features , Such as 8b10b code 、 Clock calibration and other functions ,PMA Part is analog circuit , Provide high-performance serial interface features , Such as pre weighting 、 Balance and other functions .GTX At the same time, it also provides a dynamic configuration interface , For dynamic modification GTX Configuration of .

         IBERT The loopback mode of the tool has a near end PCS Loop back test （ route ①）, Data flows only through the near end GTX Of PCS part , It can be used to verify the near end GTX in PCS Send and receive bidirectional settings ; Proximal end PMA Loop back test （ route ②, Data flows through the near end GTX Of PCS、PMA, It can be used to verify the near end GTX Send and receive bidirectional settings ; Distal PMA Loop back test （ route ③）, Data flows through the near end GTX Of PCS and PMA, distant GTX Of PMA part , Through two GTX The physical connection between , Verify two GTX The reliability of the physical connection between , And verify two GTX Of PMA Correctness of some settings ; Distal PCS Loop back test （ route ④） Verify the communication status between the near end transceiver and the far end transceiver ; as well as None Loopback free mode means sending and receiving through external connection .

Distal PCS or PMA Board download during loopback test IBERT Nucleated bit file , Through Tx and Rx Interfaces are interconnected , The mode on one of the channels is set to Far_End_PMA or Far_End_PCS Pattern , The other channel is set to the default None Mode and monitor bit error rate .

Vivado in IBERT The default mode is None Pattern , The transceiver is realized by self collection through external loopback through external connection . The same group of transceivers TX and RX Make a short circuit , stay RX The receiver receives TX After sending the data , Data sent and received by comparison , So we can get the statistical value of the error code of the receiver .

3、 ... and 、 Testing process

1、 Description of device support rate

GTP , GTX , GTH Are serial transceivers , The difference is that the speed is different , The names are different in different devices , Because in vivado Select the corresponding device model when creating the project , Use IBERT It will automatically check whether the selected line speed is within the line speed range supported by the device according to the device model .

In the example, the device model used is xc7z030ffg676-2, In the data book according to 7 series -2 Speed class and FF The device can be found in the package GTX The data rate range is 0.5~10.3125G, Therefore, in the process of testing, the test rate should be within this range .( Reference documents DS182)

2、IBERT IP Nuclear configuration

（1） Start by opening vivado, After the new project is built, start from IP Catalog find IBERT And double click to open ;

（2）IBERT Test protocol selection Custom1,GTX The reference clock selection frequency is 125MHz, In the process of configuration ,Refclk The optional frequency is determined by LineRate decision , Because on the board Refclk Fixed to 125MHz, Therefore, the line speed selected for the test should support 125MHz The reference clock of .（ With 4G Take line speed for example ）

（3） In the development board , Differential clock and MGTREFCLK0112 Connect , Therefore, reference clock selection MGTREFCLK0112.

（4） take GTX Input 125MHz At the same time IBERT Internal logic working clock , That way, you don't have to use an extra external clock .

（5） After configuration, click OK

（6） After configuration , Right click to open exampledesign engineering

（7） open exampledesign After the project , after Synthese、Implementation, Generate bit Files can be burned .

3、 test

（1） Proximal end PCS or PMA Loop back test （Near-End PCS/PMA loopback）

No external connection is required , After burning successfully , stay Serial I/O Links Window create connection , Will be the same as 1 individual GTX In the same channel TX and RX establish link.（ You can also choose auto-detectlinks）

establish link after , If five consecutive data transmissions in the link succeed , Link connectivity , Otherwise, it is disconnected . stay serial I/O link Rightmost loopback mode Select the near end PCS（ or PMA） Loopback mode , Bit errors may occur when changing the mode , Need to click reset Re monitor .

After a period of testing , Errors The value of has been 0, It indicates that there is no bit error during the test , Explain board level GTX The hardware works stably .

Eye chart can be observed more intuitively GTX Signal integrity of , Right click to connect link, choice create scan, The eye diagram can be generated .

stay Serial I/O link Window ,errors Is the number of error codes ,BER Is the bit error rate , stay reset after ,errors and BER Will revert to 0 Re count , Usually, a small amount of error code may appear after changing other parameters , At this time need reset Then re count the error code .TX Pre-Cursor and TX Post-Cursor It is pre weighted and post weighted ,TX Diff Swing For swing ,RX Pattern and TX Pattern For input 、 Output data type , Provide pseudorandom codes with different bit widths 、 Slow clock （101010……） And fast clock （11111111110000000000……）, It should be noted that the input and output data types should be set to the same type ,Loopback Mode In loopback mode , The default is None Loopless mode ,Near-End PCS Is proximal PCS Loopback mode ,Near-End PMA Is proximal PMA Loopback mode ,Far-End PCS For the far end PCS Loopback mode ,Far-End PMA For the far end PMA Loopback mode . If the signal transmission quality is not ideal , It can be done by serial I/O link Adjust the parameter settings of , Scan the eye chart again to see if there is any improvement .

In order to test GTX Bit error rate of four channels , Create multiple links, Perform near end loopback test on all four channels

（2） Distal PMA Loop back test （Far-End PMA loopback）

Burn on a board ibert Generated bit file , Connect the Tx and Rx Interface interconnection , One channel is set to Far-EndPMA Pattern , The other channel is set to None Mode and monitor bit error and eye diagram .

Create corresponding connected link And check the bit error rate and eye diagram

（3） Distal PCS Loop back test （Far-End PCS loopback）

Burn on a board ibert Generated bit file , Connect the Tx and Rx Interface interconnection , One channel is set to Far-End PCS Pattern , The other channel is set to None Mode and monitor bit error and eye diagram .

Create corresponding connected link And check the bit error rate and eye diagram

（4）None Mode testing

Board download IBERT Nucleated bit file , Then put the Tx And Rx The interface is connected , Loopback mode is set to None, Realize self collection .

Four 、 summary

Through loopback and open-loop bit error rate test , The existing problems can be judged and the actual supported rate of the board can be tested .IBERT The parameters of the high-speed serial transceiver channel can be set during operation , It also provides a variety of loopback modes and test incentive sources , And it can pass the automatic scanning test , Determine the best parameters for sending and receiving . It can meet most of the requirements of high-speed serial transceiver channel signal testing in hardware testing , It can be used in fault location and other occasions .

5、 ... and 、 matters needing attention

Use ibert When the example project is tested , Do not grasp signals or use vio nucleus .