### 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)

> 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)

> 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)

> 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)

> 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)

> 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)

> 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)

> Set the Program Priority Register to low value.

— Function: void __ppc_set_ppr_med_low (void)

> Set the Program Priority Register to medium low value.