On Mon, Feb 23, 2015 at 09:37:24AM +0000, Stathis Voukelatos wrote: > Hi Richard, > > On 18/02/15 21:08, Richard Cochran wrote: > >On Tue, Feb 17, 2015 at 02:03:30PM +0000, Stathis Voukelatos wrote: > >>The command string for packet matching is stored in module RAM > >>and consists of a sequence of 16-bit entries. Each entry includes > >>an 8-bit command code and and 8-bit data value. Valid command > >>codes are: > >>0 - Don't care > >>1 - Match: packet data must match command string byte > >>2 - Copy: packet data will be copied to FIFO > >>3 - Match/Stamp: if packet data matches string byte, a timestamp > >> is copied into the FIFO > >>4 - Copy/Done: packet data will be copied into the FIFO. > >> This command terminates the command string. > > > >Why do you need to expose this interface to user space at all? Why > >not just time stamp every frame? > > To put this into context with an example, the use case this H/W > module was originally developed for was to allow multiple audio > receivers to synchronize with a single transmitter, eg. multi-room > synchronised audio. The Linux kernel already fully supports this kind of application via the SIOCSHWTSTAMP, SO_TIMESTAMPING, and PHC mechanisms. We certainly don't need another another interface just for someone's warped hardware design. I suggest that you find a way to make your HW work within the existing frame work. > The interface needs to be public so that a user-space application > can program a command string that will match packets that belong to > the audio stream of interest, for this example. Let the user program simply use a BPF for that. > In addition returning just a timestamp would not be enough in many > cases. In the audio streaming use case mentioned above some > additional > bytes from the packet payload need to be returned (with Copy > commands) in order to associate the timestamp with a certain point > in the audio stream. The time stamp is *already* associated with a particular frame. Just tell your driver to program the hardware to: 1. time stamp every frame 2. deliver every frame Thats all you need. > >How does the "Match" command work? The frame must have one particular > >byte? That can't be right. Please explain. > > Actually, that is how the H/W works. Each Match command is followed by > a data value which must match the packet data byte at the corresponding > location. If there is no match processing of the packet stops. And just what is the "corresponding location"? Thanks, Richard -- To unsubscribe from this list: send the line "unsubscribe devicetree" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
