ethmac simulation failed

fuce

从opencores网址下载的最新版本的ethmac,用ncsim做simulation的时候，tb_eth.log中有一些报"FAILED"的case，
比如：
***********************************************************************************************
At time:              8991769
Test: TEST 10: SLIDING STOP SCAN COMMAND IMMEDIATELY AFTER WRITE
REQUEST ( WITH AND WITHOUT PREAMBLE )   
*FAILED* because
Data was not correctly written into OR read from PHY register -
control register

Heading: MAC HALF DUPLEX FLOW TEST

At time:            483196167
    Test: TEST 0: DEFER, COLL. AND LATE COLL. WHILE TRANSMITTING AND
RECEIVING FRM. AT 4 TX/RX BD ( 10Mbps )  
    *FAILED* because
    Transmit should NOT start more than 1 CLK after CarrierSense and
causing Collision  

At time:            484976407
    Test: TEST 1: DEFER, COLL. AND LATE COLL. WHILE TRANSMITTING AND
RECEIVING FRM. AT 4 TX/RX BD ( 100Mbps )
    *FAILED* because
    Transmit should NOT start more than 1 CLK after CarrierSense and
causing Collision   

At time:            955522987
    Test: TEST 1: DEFER, COLL. AND LATE COLL. WHILE TRANSMITTING AND
RECEIVING FRM. AT 4 TX/RX BD ( 100Mbps )
    *FAILED* because
    Transmit should NOT start more than 1 CLK after CarrierSense and
causing Collision  
***********************************************************************************************

请问有人碰过同样或类似的问题吗？是RTL本身的bug还是有的设置我没设好，导致的failed？
请高手的指点，谢谢！