Hot!KSZ8851SNL Local Loopback Procedure

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JHEe
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2018/06/05 11:25:41 (permalink)
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KSZ8851SNL Local Loopback Procedure

Third time's the charm...
 
I need some help with the local loopback procedure supported by the KSZ8851SNL. I have the chip fully functional for my application, but I'm adding a loopback test into a power-on-self-test routine. I can't seem to get the loopback to work. After setting the device into loopback mode, I have tried simple SPI transfers to the device and reading the data on the MISO lines (results in all 0s). I have tried writing to the transmit QMU and reading from the receive QMU (results in all 0x55s when I send 0x00-0x09 repeating). I have also verified that the register is getting set in loopback mode by reading the register before writing to the Tx QMU (gives me 0x6120).
 
I know this post isn't very clear, but this is the third time I've tried to post it, so obviously some details I had in previous posts made the forum filter unhappy. If this makes it into the forum, I'm more than happy to give more detail about what I've tried and what the scenario is.
Thanks.
-Jason
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    JHEe
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    Re: KSZ8851SNL Local Loopback Procedure 2018/07/02 11:13:53 (permalink)
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    Thanks for finally approving this post, but I figured it out in the 4 week interim. 
     
    If anyone ever needs help with this, make sure you have your transmit QMU settings correct and verify that you aren't filtering out your test packet on the receive side. Finally, to really make things work, flush your QMUs between loopback iterations. I also turned off checksum verification to make things easier.
     
    That's how I got it to work anyway. 
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