### E.1 PowerPC-specific Facilities ¶

Facilities specific to PowerPC that are not specific to a particular operating system are declared in `sys/platform/ppc.h`.

Function: `uint64_t` __ppc_get_timebase `(void)` ¶

  Preliminary: | MT-Safe | AS-Safe | AC-Safe | See POSIX Safety Concepts.

  Read the current value of the Time Base Register.

  The 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 Power ISA 2.06b - Book II - Section 5.2.

  `__ppc_get_timebase` uses the processor’s time base facility directly without requiring assistance from the operating system, so it is very efficient.

Function: `uint64_t` __ppc_get_timebase_freq `(void)` ¶

  Preliminary: | MT-Unsafe init | AS-Unsafe corrupt:init | AC-Unsafe corrupt:init | See POSIX Safety Concepts.

  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 Power ISA 2.06b - Book II - Section 5.2.

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 Power ISA 2.06b - Book II - Section 3.2.

Function: `void` __ppc_yield `(void)` ¶

  Preliminary: | MT-Safe | AS-Safe | AC-Safe | See POSIX Safety Concepts.

  Provide a hint that performance will probably be improved if shared resources dedicated to the executing processor are released for use by other processors.

Function: `void` __ppc_mdoio `(void)` ¶

  Preliminary: | MT-Safe | AS-Safe | AC-Safe | See POSIX Safety Concepts.

  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.

Function: `void` __ppc_mdoom `(void)` ¶

  Preliminary: | MT-Safe | AS-Safe | AC-Safe | See POSIX Safety Concepts.

  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.

Function: `void` __ppc_set_ppr_med `(void)` ¶

  Preliminary: | MT-Safe | AS-Safe | AC-Safe | See POSIX Safety Concepts.

  Set the Program Priority Register to medium value (default).

  The 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 `__ppc_set_ppr_med` (medium – default), `__ppc_set_ppc_low` (low) and `__ppc_set_ppc_med_low` (medium low). More information available in Power ISA 2.06b - Book II - Section 3.1.

Function: `void` __ppc_set_ppr_low `(void)` ¶

  Preliminary: | MT-Safe | AS-Safe | AC-Safe | See POSIX Safety Concepts.

  Set the Program Priority Register to low value.

Function: `void` __ppc_set_ppr_med_low `(void)` ¶

  Preliminary: | MT-Safe | AS-Safe | AC-Safe | See POSIX Safety Concepts.

  Set the Program Priority Register to medium low value.

Power ISA 2.07 extends the priorities that can be set to the Program Priority Register (PPR). The following functions implement the new priority levels: very low and medium high.

Function: `void` __ppc_set_ppr_very_low `(void)` ¶

  Preliminary: | MT-Safe | AS-Safe | AC-Safe | See POSIX Safety Concepts.

  Set the Program Priority Register to very low value.

Function: `void` __ppc_set_ppr_med_high `(void)` ¶

  Preliminary: | MT-Safe | AS-Safe | AC-Safe | See POSIX Safety Concepts.

  Set the Program Priority Register to medium high value. The medium high priority is privileged and may only be set during certain time intervals by problem-state programs. If the program priority is medium high when the time interval expires or if an attempt is made to set the priority to medium high when it is not allowed, the priority is set to medium.