Date: Thu, 6 Dec 2007 19:14:29 -0800 From: "Len Gross" <sandiegobiker@gmail.com> To: "freebsd-net@freebsd.org" <freebsd-net@freebsd.org> Subject: TDMA / Interrupts / Pre-emptible Message-ID: <27cb3ada0712061914g4aff5a7eq7d5cc64ba3d493ed@mail.gmail.com>
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I have built a "user land" prototype of a custom network protocol for an RF network. It is based on Netgraph and using Ethernet rather than real RF. Eventually, all the code will go into a special piece of hardware, but the first hardware really will look like an Ethernet card that puts messages out N microsends after they are put into its memory. Since the protocol employs some TimeDivisionMultipleAccess (TDMA), "precise" feeding of the board is important. In "userland" I seem to have about 1 ms of "delay"/variability from when I schedule a timer and when it wakes up a thread. I think this is pretty much expected behavior and is fine for algorithm testing. When I move my userland code to "driver/kernel-land" and set a timer to send a packet to some hardware how much delay / variability will I see in that timer? I think the question is more/less equivalent to the pre-emptibility of driver code and interrupts in general. (If this should go to another forum, please advise.) Thanks in advance. --Len
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