Other Parts Discussed in Thread: CDCM61002, TEST, AM5728, SYSCONFIG
I am using AMA5708 to implement x2 lane and Gen2 communication with xilinx A7 devices through PCIe. However, during use, it was found that individual AM5708 devices would have PCIe link instability, and I hope to get some troubleshooting suggestions.
The following descriptions of our hardware design and troubleshooting.
（1）The following is our hardware basic framework. The PCIe pins of AM5708 is directly connected to Xilinx-A7 GTX pins, and a 100nf capacitor is connected in series. Use CDCM61002 clock chip to provide 100MHz clock to AM5708 and Xilinx A7 respectively, as PCIe reference clock
（2）The following are the main phenomena of our PCIe failure:
expect x2 lane, gen2, actually x1 lane, gen2
expect x2 lane, gen2, actually x2 lane, gen1
expect x2 lane, gen2, in fact, AM5708 cannot perform link training normally
There are 3 sets of test abnormalities in 5 sets of boards, and there is a 1/3 probability that the test fails. The tests of the other two boards are normal.
（3）Here are some troubleshooting we have done:
① Set the desired speed to x1 lane, gen1; all boards can pass the test
② Modify the AM5708 PCIe clock source to ACSPCIE or ADPLL, the probability of test failure is the same, and there is no improvement
③ PCIe loop adds 100R terminal matching resistance, no improvement
④ Exchange the PCIe CLK capacitance of the normal board with the capacitance on the abnormal board, no improvement
⑤ The board power supply ripple is about 18.4mV, which is less than the MAX Vpp 50mV described in the manual
⑥ Hardware loopback PCIe link, using Xilinx A7 eye diagram test; the eye diagram is better, and the line signal routing quality is no problem
⑦ Interchange the AM5708 CPU of the normal board and the AM5708 CPU of the abnormal board;
The AM5708 CPU of the normal board + PCB test of the abnormal board was normal for 150 times; the AM5708 CPU of the abnormal board + PCB test of the normal board failed after 5 tests.
In summary, the PCIe link training problem currently located may be related to different AM5708 CPUs, and the error probability is relatively high.
Hope to get your troubleshooting suggestions，Thanks.