Messages in this thread | | | Date | Thu, 3 Jun 1999 18:36:35 -0400 (EDT) | From | "Richard B. Johnson" <> | Subject | Re: zero-copy TCP fileserving |
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On Thu, 3 Jun 1999, Bjorn Wesen wrote: [SNIPPED] > > Speaking of checksumming outgoing fragments in HW - it is trivial to make > the HW calculate the checksum itself, but I see a problem with having it > inserting it in the stream - mainly because the checksum field passes > through the HW _before_ the data it is supposed to checksum. How is this > solved in the HW that can do outgoing checksumming ? Does it have a FIFO > large enough to keep an MTU (and manipulate the header) ? >
I don't know. I do know that the normal CRC is not just appended in the NE* SNIC. You can 'remote DMA' data both ways and when you get it back it doesn't have the CRC. Several years ago I tried for a long time to be able to read the CRC of the packet I was about to send. We use these things are RF modulators in a UWB communications system.
It looks as though the normal CRC is appended during the actual transmit. If the offset of the checksum was known to a controller, it could fill in the checksum using the same mechanism.
Cheers, Dick Johnson ***** FILE SYSTEM WAS MODIFIED ***** Penguin : Linux version 2.2.6 on an i686 machine (400.59 BogoMips). Warning : It's hard to remain at the trailing edge of technology.
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