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Intel® PXA255 Processor Developer’s Manual 3-35
Clocks and Power Manager
Memory frequency = 3.6864 MHz crystal freq. * crystal frequency to memory frequency multiplier
(L)
Run mode frequency = Memory frequency * memory frequency to run mode frequency multiplier
(M)
Turbo mode frequency = run mode frequency * run mode frequency to turbo mode frequency
multiplier (N)
The value for L is chosen based on external memory or LCD requirements and can be constant
while M and N change to allow run and turbo mode frequency changes without disrupting memory
settings. The value for M is chosen based on bus bandwidth requirements and minimum core
performance requirements. The value for N is chosen based on peak core performance
requirements.
Table 3-20. CCCR Bit Definitions
0x4130_0000
Core Clock Configuration Register
(CCCR)
Clocks Manager
Bit
31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
reserved N M L
Reset
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 1 0 0 0 0 1
Bits Name Description
31:10 — reserved
[9:7] N
Run Mode Frequency to Turbo Mode Frequency Multiplier
Turbo mode Freq. = Run mode frequency * N
000 – reserved
001 – reserved
010 – Multiplier = 1
011 – Multiplier = 1.5
100 – Multiplier = 2
101 – reserved
110 – Multiplier = 3
111 – reserved
Set to 010 on hardware and watchdog resets.
[6:5] M
Memory Frequency to Run Mode Frequency Multiplier
Memory Freq. = Crystal Freq. * L
00 – reserved
01 – Multiplier = 1 (Run mode frequency is equal to memory frequency)
10 – Multiplier = 2 (Run mode frequency is 2 times the memory frequency)
11 – Multiplier = 3 (Run mode frequency is 4 times the memory frequency)
Set to 01 on hardware and watchdog resets.
[4:0] L
Crystal Frequency to Memory Frequency Multiplier
00000 – reserved
00001 – Multiplier = 27 (Memory Frequency is 99.53MHz from 3.6864 MHz crystal)
00010 – reserved
00011 – Multiplier = 36 (Memory Frequency is 132.71MHz from 3.6864 MHz crystal)
00100 – reserved
00101 – Multiplier = 45 (Memory Frequency is 165.89MHz from 3.6864 MHz crystal)
00110 to 11111 – reserved
Set to 00001 on hardware and watchdog resets.