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20% chance of Ping Timeout on 100M Ethernet

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tilblackout:
Hello everyone,

On my development board, I'm using the KSZ8051 as the Ethernet chip, and the official manual can be found at: https://ww1.microchip.com/downloads/aemDocuments/documents/OTH/ProductDocuments/DataSheets/KSZ8051MNL-RNL-10BASE-T-100BASE-TX-Automotive-Physical-Layer-Transceiver-DS00002310B.pdf

The CPU I used is I.MX RT1170 from NXP, which provides SDK routines for the KSZ8081. After comparing the registers of the two chips, I found that no modifications are needed in the initialization code.

In the schematic, I forgot to add pull-up resistors for MDC and MDIO during hardware design. As a temporary solution before making the next board revision, I used software pull-ups on the MCU's internal GPIO, and successfully initialized the chip.

The computer can recognize the 100M Ethernet, but when pinging my board, there is a 20% chance of timeout.


Below is the schematic


What could be the reason for this?

I would greatly appreciate any assistance.

eleguy:
1) Where do you terminate ethernet differential pair(s) with 100 ohms? Or did I miss it when quickly checking the schematics.
2) Did you do impedance controlled board?

westfw:

--- Quote ---when pinging my board, there is a 20% chance of timeout.
--- End quote ---
So "something" sends 100 ping packets, and gets 80 replies?
Does your board see 100 packets (+ a couple for ARP/etc), or 80 packets?  (ie, is it a reception problem, or a response problem?)

agehall:
It usually isn’t the problem, but do be aware that ICMP PING isn’t exactly a priority for any network stack so it may be that packets are just ignored.

If you want to be 110% sure you have a problem, measure TCP retransmission rates or something along those lines.

tilblackout:

--- Quote from: westfw on December 06, 2023, 05:00:40 pm ---
--- Quote ---when pinging my board, there is a 20% chance of timeout.
--- End quote ---
So "something" sends 100 ping packets, and gets 80 replies?
Does your board see 100 packets (+ a couple for ARP/etc), or 80 packets?  (ie, is it a reception problem, or a response problem?)

--- End quote ---
As shown in the Wireshark packet capture below, my WIN10 computer sent four ping packets, but for the third packet, there was no response from the KSZ8051 on the board.

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