Clock speed: Difference between revisions

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This document describes the format for clock speed load values. The clock speed can be set by writing to the first two registers at [[Memory-mapped_I/O_ports#900B0000_-_Power_management]]. Clock speeds are in units of MHz.
This document describes the format for clock speed load values. The clock speed can be set by writing to the first two registers at [[Memory-mapped_I/O_ports#900B0000_-_Power_management]]. Clock speeds are in units of MHz. Most of this information is derived from Nover source code.


==CX model==
==CX model==

Revision as of 00:33, 12 May 2013

This document describes the format for clock speed load values. The clock speed can be set by writing to the first two registers at Memory-mapped_I/O_ports#900B0000_-_Power_management. Clock speeds are in units of MHz. Most of this information is derived from Nover source code.

CX model

Bit 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22
Base/CPU value 48MHz base CPU/AHB value Base value Unknown
Base to CPU ratio (Base/CPU value) * (Unknown)
CPU to AHB ratio (CPU/AHB value) + 1
Base clock speed (if 48MHz base) 48
Base clock speed 6 * (Base value)
CPU clock speed (Base clock speed) / (Base to CPU ratio)
AHB clock speed (CPU clock speed) / (CPU to AHB ratio)
APB clock speed (AHB clock speed) / 2

The unknown quantity only ever seems to be either 1 or 2. It's probably a multiplier.

Classic model

Bit 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
Base/CPU value 27MHz base CPU/AHB value Base value
Base to CPU ratio (Base/CPU value) * 2
CPU to AHB ratio (CPU/AHB value) + 1
Base clock speed (if 27MHz base) 27
Base clock speed 300 - 6 * (Base value)
CPU clock speed (Base clock speed) / (Base to CPU ratio)
AHB clock speed (CPU clock speed) / (CPU to AHB ratio)
APB clock speed (AHB clock speed) / 2