NonStop S-Series Server Description Manual (G06.27+)

Principles of System Operation
HP NonStop S-Series Server Description Manual—520331-004
2-12
Sequence for Responses to Outgoing Requests
Sequence for Responses to Outgoing Requests
After the target ServerNet device has received and taken action on the request
described in the preceding topic, it sends a response packet back to the sending
ServerNet device. Figure 2-6 illustrates the actions taken when the response packet is
received back at the requesting device.
1. The incoming response packet is received by the processor ServerNet interface.
Upon examining the header of the packet, the processor ServerNet interface
determines that this is a response packet and therefore passes control to the BTE
hardware. (Only the BTE logic would be interested in incoming response packets.)
2. If the original request was a read request, the response packet contains data. The
BTE hardware, in this case, does a DMA transfer to memory, using the physical
address available in the current BTE descriptor.
3. If a page crossing is needed to complete the read or write request, the BTE
hardware advances to the next linked BTE descriptor for additional information.
(See Step 4 in the preceding topic.)
4. The BTE hardware obtains information needed to create the next packet and
transmits it to the target device through the ServerNet hardware. (Steps 7 and 8 in
the preceding topic.)
Steps 3 and 4 can be repeated several times in the case of a lengthy request, until the
end of the BTE descriptor list is reached.