System Clock Management

See sysclk_quickstart.

The sysclk API covers the system clock and all clocks derived from it. The system clock is a chip-internal clock on which all synchronous clocks, i.e. CPU and bus/peripheral clocks, are based. The system clock is typically generated from one of a variety of sources, which may include crystal and RC oscillators as well as PLLs. The clocks derived from the system clock are sometimes also known as synchronous clocks, since they always run synchronously with respect to each other, as opposed to generic clocks which may run from different oscillators or PLLs.

Most applications should simply call sysclk_init() to initialize everything related to the system clock and its source (oscillator, PLL or DFLL), and leave it at that. More advanced applications, and platform-specific drivers, may require additional services from the clock system, some of which may be platform-specific.

Platform Dependencies

The sysclk API is partially chip- or platform-specific. While all platforms provide mostly the same functionality, there are some variations around how different bus types and clock tree structures are handled.

The following functions are available on all platforms with the same parameters and functionality. These functions may be called freely by portable applications, drivers and services:

• sysclk_init()
• sysclk_set_source()
• sysclk_get_main_hz()
• sysclk_get_cpu_hz()
• sysclk_get_peripheral_bus_hz()

The following functions are available on all platforms, but there may be variations in the function signature (i.e. parameters) and behavior. These functions are typically called by platform-specific parts of drivers, and applications that aren't intended to be portable:

• sysclk_enable_peripheral_clock()
• sysclk_disable_peripheral_clock()
• sysclk_enable_module()
• sysclk_disable_module()
• sysclk_module_is_enabled()
• sysclk_set_prescalers()

All other functions should be considered platform-specific. Enabling/disabling clocks to specific peripherals as well as determining the speed of these clocks should be done by calling functions provided by the driver for that peripheral.

void	sysclk_init (void)
	Function to initialize the clock and disable clock for not required modules. More...

void sysclk_init

(

void

)

Function to initialize the clock and disable clock for not required modules.

Initialize the synchronous clock system.

This function will initialize the system clock and its source. This includes:

• Mask all synchronous clocks except for any clocks which are essential for normal operation (for example internal memory clocks).
• Set up the system clock prescalers as specified by the application's configuration file.
• Enable the clock source specified by the application's configuration file (oscillator or PLL) and wait for it to become stable.
• Set the main system clock source to the clock specified by the application's configuration file.

Since all non-essential peripheral clocks are initially disabled, it is the responsibility of the peripheral driver to re-enable any clocks that are needed for normal operation.

References CONFIG_SYSCLK_PSDIV, SYSCLK_PSDIV_8, and sysclk_set_prescalers().

Referenced by main().