Hi Jake, Thanks for your reply on the issue below. It turns out that
TIMINCA.Incvalue would not be constant and would be recomputed every sync
event(whatever it would be, for example Sync packet of PTP). It means that
FREQOUT register value should follow TIMINCA.Incvalue. It appears in
ixgbe_ptp_adjfreq_82599() in ixgbe_ptp.cWhat is usage of that pin(sdp supposed
for FREQOUT) could be?
Thanks and I'm appreciative for your assistance.
Regards, Maksim
On 04/24/2014 06:35 AM, Maksim M wrote:
> > Hi, Alex
> > In NIC 82599, there is option to generate frequency via sdp(configured
> > as out) - in data sheet it appears in red in 2.png . That frequency is
> > determined by FREQOUT0/1 register, as it appears in blue in
> > 1.png(attached here). I could not understand how that RLV is set. For
> > example, if I need 1Hz to be out via that sdp.
> > Thanks for advance, and sorry to bother.
> >
> > Regards, MaksimYou can generate frequency outputs on SDP pins, using this
> > feature,
however it depends on how you set the TIMINCA register, that determines
how fast SYSTIM advanced.
There is a limitation on this as well, that any period output of the SDP
has to be an exact multiple of twice the internal clock period that
drives the TimeSync features. For the 82599, that is documented in the
datasheet as 6.4 nanoseconds, which means the minimum period for the SDP
output will be 12.8 nanoseconds. In addition, NO period which is not an
exact multiple of 12.8 nanoseconds will be able to be generated. You
would have to keep that in mind when determining exactly what output
frequency you wanted.
Generally, the clock works by adding TIMINCA register value to SYSTIME
every internal clock tick. It also subtracts the TIMINCA value from the
FREQOUT register, storing it in an internal countdown. Once the
countdown register reaches 0, it will perform a level change on the SDP.
You would have to determine the FREQOUT value as a multiple of TIMINCA
for best behavior of a periodic output on the SDP.
Regards,
Jake
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