[PATCH] NTP: Sync time correctly when receiving broadcast updates

[Nick Withers]

On Thu, 2014-01-09 at 09:56 -0500, Gedare Bloom wrote:
> http://git.rtems.org/rtems/commit/?id=2b03a62441d63d056dbbd6de17429ae05e4dfd04

>         if ( i >= sizeof packet &&
> -               ((packet.li_vn_mode & (0x7 << 3)) == (3 << 3)) &&
> +    (((packet.li_vn_mode & (0x7 << 3)) == (3 << 3)) ||
> +     ((packet.li_vn_mode & (0x7 << 3)) == (4 << 3))) &&
>             ((packet.transmit_timestamp.integer != 0) ||
(packet.transmit_timestamp.fraction != 0)) &&
>                 0 == callback( &packet, 0 , usr_data) )
>                 return 0;

That indentation's good 'n' weird! Apparently it was before, too,
though.

> On Fri, Nov 1, 2013 at 9:59 AM,  <gedare at rtems.org> wrote:
> > From: Jim Panetta <panetta at slac.stanford.edu>
> >
> > 1) The value of rtems_bsdnet_ntpserver_count is equal to 0 when no
> >    server is set, so the check for (rtems_bsdnet_ntpserver_count < 0)
> >    in rtems_bsdnet_get_ntp() is wrong.  The check should be "<= 0".
> >
> > 2) Binding the listening socket port to 0 does not work.  Packets
> >    appear on the interface, but the recvfrom in tryServer() never
> >    returns.  Changing this to the well known NTP socket 123 allows
> >    the packets to be seen.
> >
> > 3) In tryServer(), an explicit check for NTP version 3 packets is made.
> >    If the NTP server is version 4, this check fails even though the
> >    packets seem to be the right shape.
> > ---
> >  cpukit/libnetworking/lib/rtems_bsdnet_ntp.c |    7 ++++---
> >  1 file changed, 4 insertions(+), 3 deletions(-)
> >
> > diff --git a/cpukit/libnetworking/lib/rtems_bsdnet_ntp.c b/cpukit/libnetworking/lib/rtems_bsdnet_ntp.c
> > index 4f991ff..35092ea 100644
> > --- a/cpukit/libnetworking/lib/rtems_bsdnet_ntp.c
> > +++ b/cpukit/libnetworking/lib/rtems_bsdnet_ntp.c
> > @@ -140,7 +140,8 @@ tryServer (int i, int s, rtems_bsdnet_ntp_callback_t callback, void *usr_data)
> >         }
> >
> >         if ( i >= sizeof packet &&
> > -               ((packet.li_vn_mode & (0x7 << 3)) == (3 << 3)) &&
> > +    (((packet.li_vn_mode & (0x7 << 3)) == (3 << 3)) ||
> > +     ((packet.li_vn_mode & (0x7 << 3)) == (4 << 3))) &&
> >             ((packet.transmit_timestamp.integer != 0) || (packet.transmit_timestamp.fraction != 0)) &&
> >                 0 == callback( &packet, 0 , usr_data) )
> >                 return 0;
> > @@ -174,7 +175,7 @@ int ret;
> >         }
> >         memset (&myAddr, 0, sizeof myAddr);
> >         myAddr.sin_family = AF_INET;
> > -       myAddr.sin_port = htons (0);
> > +       myAddr.sin_port = htons (123);
> >         myAddr.sin_addr.s_addr = htonl (INADDR_ANY);
> >         if (bind (s, (struct sockaddr *)&myAddr, sizeof myAddr) < 0) {
> >                 fprintf (stderr, "rtems_bsdnet_get_ntp() Can't bind socket: %s\n", strerror (errno));
> > @@ -190,7 +191,7 @@ int ret;
> >                  * and hope that there's an NTP broadcast
> >                  * server out there somewhere.
> >                  */
> > -               if (rtems_bsdnet_ntpserver_count < 0) {
> > +               if (rtems_bsdnet_ntpserver_count <= 0) {
> >                         ret = tryServer (-1, sock, callback, usr_data);
> >                 }
> >                 else {
> > --
> > 1.7.9.5
> >
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> 

-- 
Nick Withers

Embedded Systems Programmer
Room 2.26, Building 57
Department of Nuclear Physics
Research School of Physics and Engineering
The Australian National University (CRICOS: 00120C)

eMail: nick.withers at anu.edu.au
Phone: +61 2 6125 2091
Mobile: +61 414 397 446