[ntp:questions] new driver development
bruce.lilly at gmail.com
Fri Mar 18 01:44:54 UTC 2011
On Thu, 17 Mar 2011 19:57:02 +0000, Harlan Stenn wrote:
> Please see http://support.ntp.org/bin/view/Dev/RefclockShmV2
> I'm curious if we can support both POSIX and SVID SHM from the same
> codebase, and use a flag bit or a mode to select which one is used.
OK, looked at it and the bug it references. Comments:
1. one code base is probably impractical (see separate response to Dave
2. What's needed to coordinate driver and shared memory client access is
a proper semaphore or mutex, not more modes to avoid doing the job
properly. For crying out loud, Dijkstra's semaphore paper is now ca. 46
3. to get nanosecond timestamping on a non-proprietary platform implies
use of (POSIX) clock_gettime() or something like it, which uses (POSIX)
struct timespec. If one has those, one likely also has POSIX shared
memory and POSIX mutexes and semaphores. Mixing POSIX and SVID seems
like a bad idea; at some point, the SVID-specific stuff is going to go
the way of Lotus-1-2-3 (and I say that as a long time user of genuine
UNIX (Registered Trademark) System V).
4. Assuming specific sizes for an integer is a really bad idea...
"(64 bits making up the) clockTimeStamp* and receiveTimeStamp* fields"
More information about the questions