Products > Computers
Ethernet (speed) auto-negotiation
legacy:
so, I have a couple of days to play with our (my crew of crazy friends) Sonoko project, which has different boards running Linux, and the road-map is still ... sit, relax, and ... yes, it's all still a bloody mess :horse:
Anyway, one of the weird problems we have found is related to the Ethernet auto-negotiation, which is still a mystery.
Each node does bootstrap from the network via tftp, so it's very important that each node uses the maximal speed possible because the kernel image is of 8Mbyte and the ramrootfs is of 64Mbyte.
A lot of Mbyte to be uploaded :o
Each graphic node has a PowerPC405GP embedded CPU with an MII channel to the Ethernet PHY, which should be responsible for both speed { 10Mbps, 100Mbps} and {half, full} duplex auto-negotiation, while the router-node has three fast-ethernet ports configured to autonegotiate the maximal speed possible, but ... when you look at the configuration reported by U-boot on each of the graphic nodes, it randomly looks like "a deranged dog on speed" ( ;D ).
Here it is an example
--- Code: ---# tftpboot 800000 kernel
ENET Speed is 100 Mbps - FULL duplex connection (EMAC0)
Using ppc_4xx_eth0 device
--- End code ---
u-boot says 100Mbps full duplex!
Does it lie? Well, the Linux router says this
--- Code: ---# ethtool eth1
Settings for eth1:
Supported ports: [ TP MII ]
Supported link modes: 10baseT/Half 10baseT/Full
100baseT/Half 100baseT/Full
Supports auto-negotiation: Yes
Advertised link modes: 10baseT/Half 10baseT/Full
100baseT/Half 100baseT/Full
Advertised auto-negotiation: Yes
Speed: 10Mb/s
Duplex: Half
Port: MII
PHYAD: 1
Transceiver: internal
Auto-negotiation: on
Supports Wake-on: pumbg
Wake-on: d
Current message level: 0x00000000 (0)
Link detected: no
--- End code ---
10Mbps half duplex
100Mbps full duplex != 10Mbps half duplex .... do have to trust the router because a second laptop has just confirmed that the graphic node is *somehow* failing the auto-negotiate, so it has forced the link to be 10Mbps half-duplex.
In fact, the Ethernet PHY is a DP83843 chip which exposes some pins for Auto-Negotiation and other pins are used to indicate Duplex, Link, Receive and Transmit, Link, Collision, and Speed status. By reading their logic status ... yet again confirmed what the router says: 10Mbps half-duplex :palm:
So u-boot does lie!
One of the question is: why? why does it fail? It's not clear how and why the auto-negotiate protocol does work at this point.
-
Perhaps, I cannot even exclude a bug in u-boot, but in my mind, this is less convincing.
-
Anyway, I do not even know how to proceed, and where I have to investigate.
Daixiwen:
It is possible that the link starts at 100 Mbits/s in full duplex but drops to 10 Mbits/s and half duplex because of a poor connection.
If you use a computer instead, connected to the same router port with the same network cable, which speed do you get?
It could also be a bad soldering problem on the network connector or the transformer on the board.
edpalmer42:
Check your cables. Are they home made? Are they actual Cat5 or better or are they some unlabelled cable that happens to fit. I've seen people try to use 8-wire flat telephone cables. Not going to work!! :--
One odd thing I saw was with old 3Com 10/100 cards plugged into a Netgear 5 port Gigabit switch. If you used 1 meter cables, auto-negotiate would fail. Use 10 meter cables and everything worked perfectly! :-//
By the way, if it's a private setup that's not going to change, you can always force the ports on one side and/or the other to 100 Mbps. I'm not sure if you have to do both sides or not.
legacy:
--- Quote from: Daixiwen on September 18, 2019, 06:35:09 am ---It is possible that the link starts at 100 Mbits/s in full duplex but drops to 10 Mbits/s and half duplex because of a poor connection.
--- End quote ---
--- Code: ---graphic node0 === link2 === router node0 === link1 === laptop0
storage node1 === link3 === router node0
--- End code ---
my router says
link1 is 100Mbps
link2 is 10Mbps
link3 is 100Mbps
without changing the physical cables, let's replace the graphic node with a laptop2
--- Code: --- laptop1 === link2 === router node0 === link1 === laptop0
storage node1 === link3 === router node0
--- End code ---
my router says
link1 is 100Mbps
link2 is 100Mbps
link3 is 100Mbps
--- Quote from: Daixiwen on September 18, 2019, 06:35:09 am ---It could also be a bad soldering problem on the network connector or the transformer on the board.
--- End quote ---
yup, it looks like the graphic node0 is triggering the ethernet phy to the lowest configuration possible due to a bad transform.
I am going to replace it.
CaptCrash:
--- Quote ---
--- Quote from: edpalmer42 on September 18, 2019, 07:41:33 am ---One odd thing I saw was with old 3Com 10/100 cards plugged into a Netgear 5 port Gigabit switch. If you used 1 meter cables, auto-negotiate would fail. Use 10 meter cables and everything worked perfectly! :-//
--- End quote ---
wait, this maybe a serious problem here. Cables need to be very short, less than 1 meter, something like 40cm, because all nodes must stay inside a metal case.
--- End quote ---
I have come across this quite a bit with IT equipment where people use short cables to attach devices to ethernet switches. My understanding is that for active ethernet devices a minimum cable distance of 1.5m is required (approx 4').
I would expect that if you hard set the speeds of both ethernet ports and use a 1m cable it will probably work fine, otherwise use a longer cable and auto negotiate is likely to be ok.
Either way you would be much better off setting the speeds/duplex so that you dont have items changing on you and negotiating at one end differently to the other.
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