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Event flags are boolean conditions represented by a single bit,
grouped in 32bit words. All bits from a group are initially set to
zero.

An event flag group is a lightweight notification mechanism. The
application can send bitmasks to raise individual bits from the group
(i.e. group_value |= bits), or wait for the group to have at least one
bit set for satisfying the request. In the latter case, the group
value is read then cleared atomically, and the collected bits are
returned to the thread heading the wait queue.

Allow rebuilding the tree while retaining the initial build settings,
i.e.:

-C <srcdir> O= ARCH= CROSS_COMPILE= UAPI= and DESTDIR=

Signed-off-by: Philippe Gerum <rpm@xenomai.org>

d/h/m/s suffixes can be added to the value passed to -T for modifying
its meaning (days/hours/mins/secs). Defaults to secs when unspecified.

Make sure no *libc call might switch the caller of evl_attach_self()
to inband mode.

Typically, pthread_once() should happen before the EVL scheduling
parameters are set via oob_ioctl(), since the latter guarantees
out-of-band mode on return for non-weak policies but the former may
invoke a regular syscall at first invocation.

We may receive negative delta sum when sampling latency on fast
machines, use proper signedness for the divisor to prevent weird
results.

Instead, provide a basic handler which only prints out the cause for
receiving SIGDEBUG, which the application can use freely.

On architectures which export the clock source counter(s) via MMIO
like ARM, make sure to trigger the initial mapping syscall early while
we are initializing the library services, so that the next readings do
not involve any in-band syscall.

Do that by forcing a dummy call to evl_read_clock() before returning
from attach_evl_clocks().

Signed-off-by: Philippe Gerum <rpm@xenomai.org>

We might get ^C even before the first sample is received, do not issue
any stats in such a case.