tcpdump mailing list archives
Re: Link-layer header type request for libopenvizsla
From: "Matwey V. Kornilov" <matwey.kornilov () gmail com>
Date: Sat, 25 Aug 2018 23:10:46 +0300
чт, 23 авг. 2018 г. в 6:11, Guy Harris <gharris () sonic net>:
On Aug 22, 2018, at 1:57 AM, Matwey V. Kornilov <matwey.kornilov () gmail com> wrote:Current OpenVizsla data encapsulation format is described here: https://github.com/matwey/libopenvizsla/wiki/OpenVizsla-protocol-descriptionWhy are: the magic header; the size field; needed?
Hi, Answering your questions and Michael question, the url describes the data coming from the hardware as is. Its format is defined by the people developing FPGA firmware, that is currently not quite active: https://github.com/openvizsla/ov_ftdi/tree/master/software/fpga So it is unlikely that the format will change dramatically, but I just would like to follow initial format as close as possible. However, I agree that we can just use the following simple representation for pcap: struct { uint32_t timestamp; uint16_t flags; uint8_t usb_packet[]; }; OpenVizsla supports only USB 2.0: low, full and high speed.
The magic number is always the same, so it contains zero bits of information (in the Claude Shannon sense). If the size field is just the number of bytes in the Data field, it's just the total packet size (from the "length" field in pcap files, the "Original Packet Length" field in pcapng Packet Blocks, Enhanced Packet Blocks, and Simple Packet Blocks) minus the number of header bytes prepended (which would just be 5, for the flags and timestamp fields, if none of the fields mentioned above are needed). Presumably the timestamp field is useful because either it doesn't have to be converted to seconds-and-microseconds or seconds-and-nanoseconds units for pcap or 10^-N/2^-N ticks for pcapng or it's a relative timestamp and can't be conveniently converted to an absolute time stamp so that it's not redundant with the timestamp field of the pcap record or pcapng block.
-- With best regards, Matwey V. Kornilov _______________________________________________ tcpdump-workers mailing list tcpdump-workers () lists tcpdump org https://lists.sandelman.ca/mailman/listinfo/tcpdump-workers
Current thread:
- Link-layer header type request for libopenvizsla Matwey V. Kornilov (Aug 22)
- Re: Link-layer header type request for libopenvizsla Guy Harris (Aug 22)
- Re: Link-layer header type request for libopenvizsla Matwey V. Kornilov (Aug 22)
- Re: Link-layer header type request for libopenvizsla Guy Harris (Aug 22)
- Re: Link-layer header type request for libopenvizsla Matwey V. Kornilov (Aug 22)
- Re: Link-layer header type request for libopenvizsla Guy Harris (Aug 22)
- Re: Link-layer header type request for libopenvizsla Matwey V. Kornilov (Aug 25)
- Re: Link-layer header type request for libopenvizsla Guy Harris (Aug 25)
- Re: Link-layer header type request for libopenvizsla Guy Harris (Sep 12)
- Re: Link-layer header type request for libopenvizsla Matwey V. Kornilov (Aug 25)
- Re: Link-layer header type request for libopenvizsla Guy Harris (Aug 22)
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- Re: Link-layer header type request for libopenvizsla Matwey V. Kornilov (Sep 12)