Hello,
i have found an error in the ipipe-patch above.
Here ist the error description:
Our system:
Linux 3.10.28 with xenomai 2.6 patch on a PowerPC MPC5200
Error description:
We use the xenomai-(posix-skin-)function clock_gettime(
CLOCK_HOST_REALTIME, ..) to read out our system time. Thus, we set up a
NTP clock that runs on an FPGA. Later, we compare the system time and
NTP time deviations. Unfortunately we recognize in any comparison with
the nanoseconds a deviation of at least 100 million nsecs. We then
started the xenomai test suite and get the following prints on our console:
root@hbm-000a0f(NFS):/$clocktest -D -C
42
hostrt data area is
live
Sequence counter :
92323948
wall_time_sec :
1395909476
wall_time_nsec :
49
wall_to_monotonic
tv_sec : -1395754171
tv_nsec : 750313156
cycle_last :
5127088924084
mask :
0xffffffffffffffff
mult :
508284933
shift :
24
== Tested clock: 42
(CLOCK_HOST_REALTIME)
CPU ToD offset [us] ToD drift [us/s] warps max delta
[us]
--- -------------------- ---------------- ----------
--------------
0 -990145.8 -11538.531 2740 6253.3
As you can see, only 8 bits of the nanosecond value (wall_time_nsec)
will be displayed. Instrumentation (printks) has shown that these are
the most significant 8 bits of the value.
Reason:
The function tk_xtime(struct timekeeper *tk) (in file
include/linux/timekeeper_internal.h)
static inline struct timespec tk_xtime(struct timekeeper *tk)
{
struct timespec ts;
ts.tv_sec = tk->xtime_sec;
ts.tv_nsec = (long)(tk->xtime_nsec >> tk->shift);
return ts;
}
is applied twice to the system time. First in this function (in file
include/linux/timekeeper_internal.h):
static inline void update_vsyscall(struct timekeeper *tk)
{
struct timespec xt;
xt = tk_xtime(tk);
update_vsyscall_old(&xt, &tk->wall_to_monotonic, tk->clock, tk->mult);
}
and then in this function (in file /kernel/ipipe/timer.c):
void ipipe_update_hostrt(struct timekeeper *tk)
{
struct ipipe_hostrt_data data;
struct timespec xt;
xt = tk_xtime(tk);
ipipe_root_only();
data.live = 1;
data.cycle_last = tk->clock->cycle_last;
data.mask = tk->clock->mask;
data.mult = tk->mult;
data.shift = tk->shift;
data.wall_time_sec = xt.tv_sec;
data.wall_time_nsec = xt.tv_nsec;
data.wall_to_monotonic = tk->wall_to_monotonic;
__ipipe_notify_kevent(IPIPE_KEVT_HOSTRT, &data);
}
tk_xtime() makes a shift to the right on the nanoseconds. This shift is
at our clock source 24. If this shift now run twice consecutively, that
explains naturally why we only get the most significant 8 bits of the
nanosecond value.
a fix that might solve the problem, looks like this
void ipipe_update_hostrt(struct timekeeper *tk)
{
struct ipipe_hostrt_data data;
struct timespec xt;
// xt = tk_xtime(tk);
ipipe_root_only();
data.live = 1;
data.cycle_last = tk->clock->cycle_last;
data.mask = tk->clock->mask;
data.mult = tk->mult;
data.shift = tk->shift;
data.wall_time_sec = tk->xtime_sec;
data.wall_time_nsec = (long)tk->xtime_nsec;
data.wall_to_monotonic = tk->wall_to_monotonic;
__ipipe_notify_kevent(IPIPE_KEVT_HOSTRT, &data);
}
I have successfully tested this fix on our system.
Regards
Ralf
_______________________________________________
Xenomai mailing list
[email protected]
http://www.xenomai.org/mailman/listinfo/xenomai
