Hello,
 
Testing our LAN9221 driver software (bare metal implementation) reveals that transmitting a packet according to the SMSC LAN9221/LAN9221i Datasheet documentation results in the first DWORD (4 bytes) of the packet payload being dropped by the LAN9221 device for some reason.  I've been able to implement a work-around successfully by incrementing the packet byte count by 4 in both command DWORDs written to the TX data FIFO followed by a dummy DWORD followed by the actual packet contents.  Is anyone aware of this issue or of any more up-to-date documentation regarding the LAN9221/LAN9221i operation?
 
Norm