[eepro100] Is it a hardware problem?

[???]

Hello all.

I'm working on embedded PC hardware board which has 82559ER as ethernet controller.

It has 443BX chipset and the 82559ER is under PCI bus.

cat /proc/pci shows
---------------------------------------
  Bus  0, device  16, function  0:
    Ethernet controller: Intel 82559ER (rev 9).
      Medium devsel.  Fast back-to-back capable.  IRQ 11.  Master Capable.  Late
ncy=64.  Min Gnt=8.Max Lat=56.
      Non-prefetchable 32 bit memory at 0xc0000000 [0xc0000000].
      I/O at 0xf400 [0xf401].
      Non-prefetchable 32 bit memory at 0xc0020000 [0xc0020000].         
---------------------------------------

After some easy work, I've ported Linux successfully and the ethernet come up.
All networking applications were going very well and I could telnet, ftp, ping and browsing the web everywhere.

But, after some tough test I've found that this board crashes every time when very high network load is applied.

The symptoms are as below
-----------------------------------------------
1. I mounted a NFS server and did a copy test.
e.g.) 
# mount -t nfs nfs_server:/dir /mnt/disk
# cp -av /mnt/disk/A /mnt/disk/B                   
                (A is a directory which has all files of default RedHat7 root file system, over 500MB)
.....
.....
<crash at random time>

2. I booted this hardware board with nfs root and queried rpm database.
e.g.)
# cat /proc/mounts
/dev/root / nfs rw,v3,nolock,addr=nfs_server 0 0
# rpm -qa
.....
.....
<crash at random time>
------------------------------------------------


With the same kernel, I can boot stock 443BX mainboard with 82559 NIC.
And, it never crash with the same test. - So, it's not a NFS problem -

In stock 443BX board with 82559 NIC, cat /proc/pci shows 
-----------------------------------------
  Bus  0, device  19, function  0:
    Ethernet controller: Intel 82557 (rev 8).
      Medium devsel.  Fast back-to-back capable.  IRQ 11.  Master Capable.  Late
ncy=32.  Min Gnt=8.Max Lat=56.
      Non-prefetchable 32 bit memory at 0xfebff000 [0xfebff000].
      I/O at 0xef00 [0xef01].
      Non-prefetchable 32 bit memory at 0xfea00000 [0xfea00000].
-----------------------------------------


The differences between custom and stock boards are ethernet controller type (82559ER and 82559) and "Latency" field of /proc/pci messages.

I've tested 82559 device drivers - with many parmeter change - of D. becker, standard 2.2.18 and Intel, but no difference.

Is it a hardware problem, BIOS problem or device driver problem? - I used custom BIOS. -

Please help me.

Thanks in advance.