RCC

libopencm3 LM4F Clock control API More...

Collaboration diagram for RCC:

Modules
	Low-level clock control API
	High-level clock control API

Detailed Description

libopencm3 LM4F Clock control API

Author

© 2012 Alexandru Gagniuc mr.nu.nosp@m.ke.m.nosp@m.e@gma.nosp@m.il.c.nosp@m.om

The LM4F clock API provides functionality for manipulating the system clock, oscillator, and PLL. Functions are provided for fine-grained control of clock control registers, while also providing higher level functionality to easily configure the main system clock source.

The following code snippet uses fine-grained mechanisms to configures the chip to run off an external 16MHz crystal, and use the PLL to derive a clock frequency of 80MHz.

// A divisor of 5 gives us a clock of 400/5 = 80MHz
#define PLLDIV_80MHZ 5
 
// Enable the main oscillator
rcc_enable_main_osc();
 
// Make RCC2 override RCC
rcc_enable_rcc2();
 
// Set XTAL value to 16MHz
rcc_configure_xtal(XTAL_16M);
// Set the oscillator source as the main oscillator
rcc_set_osc_source(OSCSRC_MOSC);
// Enable the PLL
rcc_pll_on();
 
// Change the clock divisor
rcc_set_pll_divisor(PLLDIV_80MHZ);
 
// We cannot use the PLL as a clock source until it locks
rcc_wait_for_pll_ready();
// Disable PLL bypass to derive the system clock from the PLL clock
rcc_pll_bypass_disable();
 
// Keep track of frequency
lm4f_rcc_sysclk_freq = 80E6;

The same can be achieved by a simple call to high-level routines:

// A divisor of 5 gives us a clock of 400/5 = 80MHz
#define PLLDIV_80MHZ 5
 
rcc_sysclk_config(OSCSRC_MOSC, XTAL_16M, PLLDIV_80MHZ);