On Tue, Feb 17, 2015 at 11:34:26AM +0100, Axel Holzinger wrote: > as you Richard were the main force doing the work for adding hardware > timestamping to the Linux kernel, could you enlight me how the association > of a timestamp residing in kernel space (I guess in the ethernet device > driver's domain) and a PTP message is handled by the kernel? I'm asking > myself which PTP message fields actually are chosen to get the right > timestamp for a message. Or is every network packet timestamped and the > association is done by a hash or crc or something similar?
This is done differently in every driver, depending on the hardware. Some hardware provides the time stamp "in band", for example in the frame's buffer descriptor or in the frame data. In this case, the association is clear. Other (worse) hardware provides the time stamp "out of band", separate from the frame, in a time stamp fifo for example. Sometimes there is no fifo but rather a single register! In these cases, the driver must somehow match the time stamp with a frame. Some hardware provides various matching fields with the time stamp, like sequence number, message type, or a hash over multiple fields. It all depends on the hardware. If you look into various drivers, you will find functions called match(). There you can see exactly what fields are used. HTH Richard ------------------------------------------------------------------------------ Download BIRT iHub F-Type - The Free Enterprise-Grade BIRT Server from Actuate! Instantly Supercharge Your Business Reports and Dashboards with Interactivity, Sharing, Native Excel Exports, App Integration & more Get technology previously reserved for billion-dollar corporations, FREE http://pubads.g.doubleclick.net/gampad/clk?id=190641631&iu=/4140/ostg.clktrk _______________________________________________ Linuxptp-devel mailing list Linuxptp-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/linuxptp-devel
