The aim of this clock driver hook was to stop clock tick interrupts at
some late point in the exit() procedure.
The use of atexit() pulls in malloc() which pulls in errno. It is
incompatible with the intention of the
CONFIGURE_DISABLE_NEWLIB_REENTRANCY configuration option.
The exit() function must be called from thread context, so accompanied
clock tick interrupts should cause no harm. On the contrary, someone
may assume a normal operating system operation, e.g. working timeouts.
Remove the Clock_driver_support_shutdown_hardware() clock driver hook.
Close#3436.
Use the standard ARMv7-M systick module for the ARMv7-M CPU counter
instead of DWT counter since the DWT counter is affected by power saving
states.
Use an inline function for _CPU_Counter_difference() for all ARM BSPs.
Update #3456.
Add rtems_counter_frequency() API function. Use it to initialize the
counter value converter via the new system initialization step
(RTEMS_SYSINIT_CPU_COUNTER). This decouples the counter implementation
and the counter converter. It avoids an unnecessary pull in of the
64-bit integer division from libgcc.
Update #3456.
