Learn about AVR system clocks and clock options

Clock design has become a more and more difficult problem in embedded system design due to the increase in system complexity, integration and speed. Therefore, knowing more about clocks will be beneficial to the design of the entire system.
Clock system and its distribution
Figure 11 shows the main clock system and its distribution in AVR. At any given time, it is not necessary for all these clocks to be active. In order to reduce power consumption, the clock to a certain module can be stopped by various sleep modes, such as "power management and sleep mode" to be learned later. The clock system will be explained in detail below.
(Note: Since power consumption has become a problem, computers have learned to sleep; or vice versa, bionic)
Figure 11. Clock distribution

CPU clock--C clkCPU
CPU clock is introduced to the part of the system related to the operation of the AVR kernel. Examples of such modules are the general register file, status register and data memory that stores the stack pointer. Stopping the CPU clock will disable the operation and calculation of the kernel.
I/O clock--C clkI/O
I/O clock is used by most I/O modules, such as timer/counter and USART. The external interrupt module also uses the I/O clock, but note that some external interrupts are detected by asynchronous logic, and such interrupts can be detected even if the I/O clock is stopped.