Hi, Based on the example of Fast Port usage of the book programming IXP1200 (intel press), I made the following observation. (If familiar please respond). The example uses sop_seq field from rcv_ctl register in order to put the MPKTs of a PACKET in the correct order. However, in general, using the sop_seq allows for only 16 different MPKTS. That is, the number rolls over after 0xF. A 1500bytes PACKET results in 24 MPKTS. If more than one thread handle these MPKTS in parallel, there is a possibility for two threads to receive the same sop_seq. Another relative issue is the next one : In the book it is written that the sop_seq field of rcv_cntl register, follows the values of the sop_seq register. This is wrong. The sop_seq register changes only when an SOP-MPKT is received, while the sop_seq field in rcv_cntl register behaves as described in the book. (Always increases, and get the sop_seq value when a SOP-MPKT is received). To support this behavior there are two counters (documented in hardware reference manual) Now the question is this : If a thread, after the ctx_wait(start_receive) executes two back-to-back csr_reads : csr_read(sop_seq, sync_none); csr_read(rcv_cntl, ctx_wait); will end up having two sop_seq: The value of the register and the field of rcv_cntl. Will the value of the register be the sop-seq number that was assigned to the PACKET that this thread is working for ? I think the answer is "no necessarily"! Yannis Charitakis haritak@ics.forth.gr