Intel® PXA255 Processor Developer’s Manual 3-35
Clocks and Power Manager
Memory frequency = 3.6864MHz crystal freq. * crystal frequency to memory frequency multip lier
(L)
Run mode frequency = Memory frequency * memory frequency to run mode frequency multiplier
(M)
Turbo mode frequency = run mode frequen c y * 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 freq uen cy cha nge s wi tho ut d isru pti ng memo ry
settings. The value for M is chosen based on bu s bandwidth requirement s 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 – res erve d
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 3.6864MHz crystal)
00010 – reserved
00011 – Multiplier = 36 (Memory Frequency is 132.71MHz from 3.6864MHz crystal)
00100 – reserved
00101 – Multiplier = 45 (Memory Frequency is 165.89MHz from 3.6864MHz crystal)
00110 t o 11111 – r eserv ed
Set to 00001 on hardware and watchdog resets.