Datasheet

ZEUS Embedded Linux Development Kit Quickstart RedBoot

CPU core clock frequency and the clock command

RedBoot on the ZEUS initialises the core, system bus, and memory controller clocks to

104 MHz. RedBoot provides an additional command (clock), which can be used to set

the clocks to a subset of the frequencies described in section 3.5 of the PXA270

Developer’s Manual (clock implicitly sets CCCR[A], CLKCFG[B] and CLKCFG[T]). The

clock command takes parameters for the L (Run-mode to oscillator ratio) and N (turbo-

mode to run-mode ratio) settings, which determine the various clocks according to the

following formulae:

• Turbo-mode frequency = 13 MHz * L * N

• Run-mode frequency = 13 MHz * L

• System bus frequency = 13 MHz * L

• Memory controller frequency = 13 MHz * L

• LCD frequency = 13 MHz * L / K,

where K = 1 (L = 2-7), K = 2 (L = 8-16), or K = 4 (L = 17-31).

The value of N should be twice the actual value. Therefore, to set N to 1.5, pass the

option –N 3. For example:

• To set the core clock frequency to 312 MHz, and the system bus and memory

controller clocks to 208 MHz enter:

RedBoot> clock –L 16 –N 3

• To set the core clock frequency to 520 MHz, and the system bus and memory

controller clocks to 208 MHz enter:

RedBoot> clock –L 16 –N 5

Do not exceed the maximum core clock frequency specified by the particular

PXA270 fitted on the board.