|R0||8 (Reason code)|
|R1||Desired ‘slow’ speed, as index|
|R2||Desired ‘fast’ speed, as index|
|R1||New ‘slow’ speed, as index|
|R2||New ‘fast’ speed, as index|
The purpose of this call is to allow the user to select the clock speeds that are associated with Portable_Speeds ‘slow’ and ‘fast’ settings. The values the user supplies in R1 and R2 will clamped to lie between the minimum and maximum speed indices, and the updated values, representing the new speeds that will actually be used, will be returned to the caller.
Portable_Speed2 2 provides similar functionality to this call, but the speeds are expressed as MHz values, not as indices into the list of available speeds.
Due to hardware restrictions or for performance reasons, most systems will only support a limited number of CPU clock rates. Portable_Speed2 4, Portable_Speed2 5, and Portable_Speed2 6 allow the user to enumerate the list of available clock rates. Index 0 is always the slowest available speed, and (return value of Portable_Speed2 4)-1 is always the highest available speed.
To read the currently configured ‘slow’ and ‘fast’ speeds, use Portable_Speed2 9.
To read the current CPU speed, see Portable_Speed2 7.