Crystal core MPU Clock rate differences

Question

I have a embedded system which on boot up shows as below:

Clocking rate (Crystal/Core/MPU): 12.0/400/1000 MHz

Can anybody explain me on differences between these three clock rate. Processor is ARMv7, OMAP3xxx

Answer 1

As Clement mentioned, the 12.0 is the frequency in MHz of the external oscillator. Core and MPU are the frequencies of the internal PLL's.

The MPU is the Microprocessor Unit Subsystem. This is the actual Cortex-A8 core as well as some closely related peripherals. So your MPU is running at 1000 MHz or 1GHz. This is similar to the CPU frequency in your computer.

In the AM335x, the Core PLL is responsible for the following subsystems: SGX, EMAC, L3S, L3F, L4F, L4_PER, L4_WKUP, PRUSS IEP, Debugss. The subsystems may differ slightly based on the particular chip you are working with. Yours is running at 400MHz. This can be thought of as similar to the Front Side Bus (FSB) frequency in your computer though the analogy isn't exact.

Answer 2

12 Mhz is the frequency of the crystal oscillator present on the board to give a time reference.

A TI OMAP contains 2 cores : an ARM and a DSP. The terminology used here is not clear but it may be the frequencies of these cores. Check you datasheet to be sure.