Soc Clock System

First, SOC (Systern on chip system-level chip) clock system introduction

1.1 What clock. Why does the SOC need clocks

(1) The clock is the synchronized beat of the synchronous working system.

(2) There are many devices inside the SOC, such as CPU, serial port, DRAM controller, GPIO and other internal peripherals, these things to work with each other, need a synchronous clock system to command, this is the SOC clock.

1.2 How the clock is generally obtained.

(1) The clock acquisition of the SOC is generally:

* External direct input clock signal, SOC has a pin used for external clock signal, with very little

* External crystal oscillator + internal clock generator, most of the low-frequency single-chip computer is so working.

* External crystal + internal clock generator + internal PLL generates high frequency clock + inner part frequency to get clocks of various frequencies, 210 belongs to this.

1.3s5pv210 belongs to the third, why so design.

(1) Why do not use the external high-frequency crystal oscillator to generate high-frequency signal directly to the CPU.

Because the chip external circuit is not suitable for the use of high frequency, conduction radiation is more difficult to control, high-frequency crystal more expensive.

(2) Why the internal first high frequency and then in the crossover.

Since there are a lot of missing clocks inside the SOC and different clock frequencies are required, it is impossible to unify the supply, so the design idea is to get a high frequency after the PLL

(1GHZ, 1.2GHZ), and then each peripheral has its own divider to divide to get the frequency you want.

1.4 Clock and system performance relationship, overclocking, stability

(1) The General Soc clock frequency can be artificially programmed control, the frequency of the high and low on the system performance has a great relationship.

(2) s5pv210 recommended operating frequency is 800hz-1.2ghz, generally we are set 1GHZ frequency. If set to 1.2GHZ is called overclocking. System performance will increase when overclocking, but the heat will increase,

The system is unstable and the required cooling conditions are more demanding.

1.5 Correlation of clock and peripheral programming

Each peripheral work requires a certain frequency of clock, these clocks are provided by the clock system, the clock system can be programmed to control the operating mode, so we programmers can set the clock source for each peripheral, clock division system, so that the work of the peripheral clock.

1.6 The relationship between clock and power control

(1) in the SOC in various equipment work, the higher the clock frequency, the greater the power consumption, the greater the heat, the more prone to instability, the need for peripheral cooling conditions more stringent.

(2) There are many peripherals inside the SOC, which is best to turn off when not in use (do not turn off to a certain extent waste of electricity), switch peripherals are not through the switch, but through the clock. That is, we cut off the clock for a peripheral, and the peripheral doesn't work.