[ixp1200] [ixp2400] What kind of difference ixp2800 and ixp2400?

Hello~~^^ I was developed to sdk 3.1 in ixp2400. Um... I buy ixp2400/ixp2800 Programming on Amazon. MSF device is SPI4 in ixp2800 but ixp2400 is POS-PHY Level 3. What kind of difference ixp2800 and ixp2400? I hold only one of scratch ring for single PHY. Therefore, scatch ring size hold 1024. Right ? ... ... MSF_interrupt_status = 0x0000 0e00 May be, no rbuf element was free to accept mpacket. Please, solve me~~! Thanks in advance.