@node Platform, Contributors, Maintenance, Top
@c %MENU% Describe all platform-specific facilities provided
@appendix Platform-specific facilities

@Theglibc{} can provide machine-specific functionality.

@menu
* PowerPC::           Facilities Specific to the PowerPC Architecture
@end menu

@node PowerPC
@appendixsec PowerPC-specific Facilities

Facilities specific to PowerPC that are not specific to a particular
operating system are declared in @file{sys/platform/ppc.h}.

@deftypefun {uint64_t} __ppc_get_timebase (void)
Read the current value of the Time Base Register.

The @dfn{Time Base Register} is a 64-bit register that stores a monotonically
incremented value updated at a system-dependent frequency that may be
different from the processor frequency.  More information is available in
@cite{Power ISA 2.06b - Book II - Section 5.2}.

@code{__ppc_get_timebase} uses the processor's time base facility directly
without requiring assistance from the operating system, so it is very
efficient.
@end deftypefun

@deftypefun {uint64_t} __ppc_get_timebase_freq (void)
Read the current frequency at which the Time Base Register is updated.

This frequency is not related to the processor clock or the bus clock.
It is also possible that this frequency is not constant.  More information is
available in @cite{Power ISA 2.06b - Book II - Section 5.2}.
@end deftypefun

The following functions provide hints about the usage of resources that are
shared with other processors.  They can be used, for example, if a program
waiting on a lock intends to divert the shared resources to be used by other
processors.  More information is available in @cite{Power ISA 2.06b - Book II -
Section 3.2}.

@deftypefun {void} __ppc_yield (void)
Provide a hint that performance will probably be improved if shared resources
dedicated to the executing processor are released for use by other processors.
@end deftypefun

@deftypefun {void} __ppc_mdoio (void)
Provide a hint that performance will probably be improved if shared resources
dedicated to the executing processor are released until all outstanding storage
accesses to caching-inhibited storage have been completed.
@end deftypefun

@deftypefun {void} __ppc_mdoom (void)
Provide a hint that performance will probably be improved if shared resources
dedicated to the executing processor are released until all outstanding storage
accesses to cacheable storage for which the data is not in the cache have been
completed.
@end deftypefun

@deftypefun {void} __ppc_set_ppr_med (void)
Set the Program Priority Register to medium value (default).

The @dfn{Program Priority Register} (PPR) is a 64-bit register that controls
the program's priority.  By adjusting the PPR value the programmer may
improve system throughput by causing the system resources to be used
more efficiently, especially in contention situations.
The three unprivileged states available are covered by the functions
@code{__ppc_set_ppr_med} (medium -- default), @code{__ppc_set_ppc_low} (low)
and @code{__ppc_set_ppc_med_low} (medium low).  More information
available in @cite{Power ISA 2.06b - Book II - Section 3.1}.
@end deftypefun

@deftypefun {void} __ppc_set_ppr_low (void)
Set the Program Priority Register to low value.
@end deftypefun

@deftypefun {void} __ppc_set_ppr_med_low (void)
Set the Program Priority Register to medium low value.
@end deftypefun
