[Xenomai-core] Synchronising TSC and periodic timer

[Jan Kiszka <jan.kiszka@domain.hid>]

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Hi,

for those who haven't followed the endless "RTDM and Timer functions"
thread: we are currently discussing a way to provide high-resolution
timestamps in periodic mode for RTDM users. It was suggested to use the
TSC for this, but I noted that this source will not be in sync with the
periodic system timer and may even be out of sync across multiple CPUs.

A straight-forward approach to overcome this might be to record the
current TSC value together with the current jiffies in
xntimer_do_tick_periodic(). This tuple (per CPU) could then be provided
to skin implementers in order to let them offer a high-resolution
timestamp source even in periodic mode. Hmm, sounds too simple actually,
so I'm waiting now for someone pointing out the pitfalls.

Jan


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