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How to resolve MPC8260 FCC3 Ethernet Tx Underrun Error

Question asked by Gowri Sankar Y on Jun 19, 2015
Latest reply on Sep 7, 2015 by LPP

In our application SBC1 & SBC2 of below configuration are

connected for point to point communication via FCC3 100 BaseFx

Fiber Ethernet port.

As per our application SBC1 has to transfer 250KB of data to

other SBC2 within 100msec via FCC3 link regularly at every 100 msec.

During this process FCC3 Transmitter is encountering Tx

underrun errors, on an average 1 or 2 frames per second,

at the other end, receiver is getting equal number of Rx CRC errors.


if these errors are ignored and continue to run the application,

after some time (few hours), a flood of tx underrun errors are

generated suddenly and eventually leads to total link failure of FCC3 ethernet port.


If the data size is further increased then the failure comes too

early in above case.


We have verified all TX & RX buffer descriptors for FCC1, FCC2

& FCC3 and seems to be OK.


We are unable to trace the root cause of this issue.

We are also suspecting partial crash of CPM or any timing errors.

Please help us to resolve the issue.


MPC8260 SBC configuration:

MPC8260ACZUMIBB based SBC which has FCC1, FCC2, & FCC3 configured in Ethernet mode,

SCC & MCC are not connected at all, 60x Bus configured in single mode and

interfaced to FLASH(16MB + 16MB), SRAM(1 MB) and SDRAM(128MB).


Clocks: Core -266 MHz, CPM - 200 MHz and Bus - 66 MHz


FCC1 --- 10/100 baseT PHY

FCC2 --- 10/100 baseT PHY

FCC3 --- 100 baseFx PHY (Fiber optic)


FCCn Buffer descripters are located in DPRAM and Data Buffers

are in 60x Bus SDRAM.