> Over the weekend we performed some hardware modifications > on our boards with their troublesome gigabit interfaces. > > We performed a couple of tests, one of which may be > the solution to our problem. > > 1) Modified the value of the series termination of EC_GTX_CLK125 > > The PHY drives a 125MHz clock signal to the PowerPC > (EC_GTX_CLK125 signal) when operating in gigabit ethernet > mode. > > Our schematic used a 33-Ohm series termination on this > 125MHz signal, but we had used 22-Ohms for all other series > terminations. The MDS board also uses 22-Ohms series > terminations. > > We replaced the 33-ohm termination with 22-ohms ... and > things started working. We looked at the 125MHz signal at > the destination pin on the BGA of the PowerPC using > a high-bandwidth scope (2GHz LeCroy) for both 22-Ohms > termination and 33-Ohms, and there is a slight > difference in waveform shape, but no obvious ringing, > or steps in the clock edges that might suggest > transmission line reflections. > > The fact that we only ever observed errors in gigabit > mode, that the PHY never reports any errors, > that EC_GTX_CLK125 is only used in gigabit mode, > and that the data errors looked like a FIFO clocking > issue, is consistent with the error being related to > the quanlity of the EC_GTX_CLK125 signal. > > I'm not ready to claim success, as I need to make the > change on other boards ... but its very encouraging!
Good news, Dave. Sure, we need to keep the imdependence matching. change the series resister. Anyway, I strong recommand you to check if the signal of GMII interface meet the H/W spec of 8349EA. > 2) Frequency accuracy testing > > We replaced the PHY 125MHz clock source (an onboard > oscillator) with a frequency synthesizer driven into > a buffer (to create a 3.3V logic level clock). > > The frequency was adjusted to 124.90MHz, 124.95MHz, > 125.00MHz, 125.05MHz, and 125.10MHz. Errors were > generated for the +/-0.1MHz cases, but things worked > fine for the +/-0.05MHz offsets. > > So the PHY is tolerant of frequency errors in the > oscillator. > > (This test was performed after the series termination > had been changed). > > > Ira is going to boot the working board with Linux and > perform some network stress tests. > > I'll modify some other boards, and we'll tests those too. > > Cheers, > Dave > > > > _______________________________________________ U-Boot mailing list U-Boot@lists.denx.de http://lists.denx.de/mailman/listinfo/u-boot
