Subject: Re: gem (ERI/GEM/GMAC Ethernet device driver) has problems on macppc
To: Miles Nordin <carton@Ivy.NET>
From: Timo Schoeler <>
List: current-users
Date: 10/21/2005 09:53:40
Miles Nordin wrote:
>>>>>>"ts" == Timo Schoeler <> writes:
>     ts> all done, i've even used different switches -- always the
>     ts> same.
> What do you mean:
>     >>> * running in full duplex mode not a single error occurs (i
>     >>> used a 4GByte file and transferred it via ftp);
> you say the problem is always the same no matter what you do, but you
> also said it works fine with Nortel switch and manually set to
> full-duplex, which makes me confused.  Which is true?

no, i didn't say this.

i said on a plain dumb SMC 10/100 _hub_ this problem appears. then i 
tried the Nortel 450 (_switch) -- this runs fine in full duplex mode. 
when i then manually set both the switch (managed) and the G4 to half 
duplex, the problem occurs again.

when using the SMC _hub_ the machine automatically sets the NIC to half 
duplex as it should be.

> Duplex autodetection is a little unpredictable, but one of the common
> rules is that either both sides need to be configured manually, or
> both sides need to be set to Auto.  For example, if you set your Mac
> to 'auto' and then set the switch manually to forced-fullduplex, then
> the Mac will autodetect half-duplex, and you'll have a duplex
> mismatch.  It is quite goofy and isn't guaranteed to behave that way
> all the time, but that is how it's _supposed_ to behave in theory, and
> even the theoretic behavior is not intuitive.

yes, but usually in such an environment (colliding half and full duplex 
setting) the transfer rates are very very low. this is not the case here.

> I think this is the usual reference people give:
> I have had a lot of duplex problems at my house, because I carefully,
> deliberately use 100mbit/s-only hubs exclusively, no switches and
> certainly none of those disgusting ``dual-speed hubs''.  Realtek NICs
> don't correctly autodetect the hubs and simply ignore their duplex
> setting, and they fail using their supported proprietary Windows
> driver even.  The Realtek Crab has become the household symbol for
> utter crappyness and failure.  The weirdest problem I had was, an XBox
> onboard NVidia NIC would get partitioned by the managed hub (link
> light went green->orange) about once every two weeks, and it would
> stay Orange/useless until I reboot the XBox.  The problem went away
> when I got all machines with bad duplex settings off the segment---the
> spew on the segment was somehow exercising a nasty intermittent bug in
> the XBox NIC's Linux driver.
> Everyone always says ``it can't be MY machine, i set it to half just
> like you said,'' or ``but that's a good 3com card it couldn't POSSIBLY
> be the culprit'' or ``i used Linux eth-tool and it said it was fine''
> or ``but that machine works fine, it's this OTHER machine that's the
> slow one'' or ``look at the collision light it's solid red, that's why
> i'm losing so many packets'' (Ethernet collisions are *NOT* lost
> packets).

i didn't write this either. i wrote of CRC errors and retransmits.

> WHATEVER, and blame it on my use of hubs or throw up their
> hands and say the problem is just impossible to solve, and every time
> I track it down to some guilty machine with combinations of flood
> pings and big ftp downloads involving three or four machines at once,
> incriminate the Realtek Crab _again_ and shame its owner into fixing
> it, and then everything works great again.  When duplex is wrong
> NetBSD's tlp driver scrolls 'CRC error' and 'dribbling bit' messages
> so fast that the system clock starts to lose time.
> ...i had odd experiences in passing with bmac adapters so,...I
> wouldn't rule out a bug in the gmac driver.  I'm just saying, if
> people tell you to suspect duplex problems and diagnose it from that
> angle, don't poo-pooh them: it's real and it's tricky.

er, sorry, i re-checked all my mails on this topic and i really didn't 
'poo-pooh' anyone -- at least to my understanding. if i did, i'm really 
sorry and would like to kindly ask anybody who saw this to point me to 
this issue so that i can learn from it (serioulsy!).