MPC5777C: Problems sending ethernet frames while debugging

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MPC5777C: Problems sending ethernet frames while debugging

466 Views
BG
Contributor II

Hello,

We are developing an application utilising the FEC of the MPC5777C using the evaluation board MPC5777CEVB. The FEC is operated in the MII-Lite mode and the data cache is deactivated.

Problem description:

When no debugger is attached we have detected no problems for both sending and receiving frames.

But when we attach a Trace32 debugger and add a breakpoint to a called function, e.g., the FEC-send-function, all frames sent by the MCU are marked as defective by the receiver and a CRC/align error is indicated. When the breakpoint is deactivated and the execution resumed everything works again.

This error is visible in the following configurations:

  1. when the EVB is connected to an Ethernet card of a PC;
  2. When an external loopback is used utilising a cut cable for which the Rx and Tx pairs are connected. In this case the promiscuous mode (RCR[PROM]) has to be set as well to be able to receive the sent packet. When looking at the Tx and Rx buffers the received message seems to be correct and identical to the sent message. In this case we also detected one error each time the manual break command of the debugger, even if no breakpoint is active.

This problem does not manifest itself when we are using the MII internal loopback as described in the reference manual on page 2486 f..

It is also not present when we add a breakpoint to an uncalled function so that it is never activated.

 

Question:

  1. Is there any known interference between the debug module and the FEC?
  2. Are there any troubleshooting steps which we could try?

 

Regards,

Bernd

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2 Replies

442 Views
PetrS
NXP TechSupport
NXP TechSupport

Hi,

the only idea I have is some sort of signal interference. Thus you can try...
- decrease MII speed, or check difference of 10vs100Mbit.
- test different slew rate for output pins and enable HYS for inputs
- decrease JTAG speed

BR, Petr

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404 Views
BG
Contributor II

Hello Petr,

thank you for the suggestions! While trying them I noticed that I had incorrect GPIO settings:

  • Pull-ups or pull-downs were active for all FEC pins.
  • I had set the slew control for the output pins when they were not set in the example project.

Correcting those errors solved my problem.

I find it curious that it it worked at all. Do you have an idea why this caused problems only when the debugger was active?

Regards, Bernd

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