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iMX253 using MII interface

Question asked by Greg Ungerer on Apr 23, 2013
Latest reply on Aug 8, 2013 by Greg Ungerer
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Hi All,

 

I am working with a new custom board based around the iMX253. For the most part it is working. Booting up from SPI flash with u-boot and linux (3.8) all running fine.

 

The board is wired with a Realtek 8201 PHY hanging of the FEC module. So it is wired in full MII mode. Now it mostly works. u-boot can network load, and under linux the interface works. But it is occasionally losing packats - from both u-boot and linux. Quite noticeable when u-boot has to retry while tftp loading. Flood pinging from linux shows a loss rate of around 1 to 2 packets a second.

 

Looking at the FEC lines from the iMX253 to the 8201 PHY on an oscilloscope both RDATA0 and RDATA1 look pretty good, but RDATA2 and RDATA3 don't look anywhere near as good - they look a little runty and don't push up anywhere near 3.3v. Thinking this might be the source of my packet loss.

 

I have played around with the PAD/pin settings but nothing seems to improve the signal quality on those lines.

 

Does anyone else have experience using something like the iMX253 in full MII mode to a PHY?

Any tricks to getting it working right?

 

Regards

Greg

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