ref: d812bca336c8d67a5b1a9744b36c0ecbb5baa8b3
dir: /demos/stm32f429_disco/pll.c/
/*
* Copyright (c) 2013 Grzegorz Kostka (kostka.grzegorz@gmail.com)
* All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
*
* - Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* - Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
* - The name of the author may not be used to endorse or promote products
* derived from this software without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
* IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
* OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
* IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
* INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
* NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
* DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
* THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
* (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
* THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*/
#include <config.h>
#include <pll.h>
#include <stm32f4xx.h>
#define PLL_FREQUENCY CFG_CCLK_FREQ
#define PLL_CRYSTAL 8000000UL
static void flash_latency(uint32_t frequency)
{
uint32_t wait_states;
wait_states = frequency / 30000000ul; // calculate wait_states (30M is valid for 2.7V to 3.6V voltage range, use 24M for 2.4V to 2.7V, 18M for 2.1V to 2.4V or 16M for 1.8V to 2.1V)
wait_states &= 7; // trim to max allowed value - 7
FLASH->ACR = wait_states; // set wait_states, disable all caches and prefetch
FLASH->ACR = FLASH_ACR_DCRST | FLASH_ACR_ICRST | wait_states; // reset caches
FLASH->ACR = FLASH_ACR_DCEN | FLASH_ACR_ICEN | FLASH_ACR_PRFTEN | wait_states; // enable caches and prefetch
}
static void fpu_enable(void)
{
#if (__FPU_PRESENT == 1) && (__FPU_USED == 1)
SCB->CPACR |= ((3UL << 10*2)|(3UL << 11*2)); // set CP10 and CP11 Full Access
#endif
}
void pll_init(void)
{
uint32_t div, mul, div_core, vco_input_frequency, vco_output_frequency, frequency_core;
uint32_t best_div = 0, best_mul = 0, best_div_core = 0, best_frequency_core = 0;
fpu_enable();
RCC->CR |= ((uint32_t)RCC_CR_HSEON); // enable HSE clock
flash_latency(PLL_FREQUENCY); // configure Flash latency for desired frequency
for (div = 2; div <= 63; div++) // PLLM in [2; 63]
{
vco_input_frequency = PLL_CRYSTAL / div;
if ((vco_input_frequency < 1000000ul) || (vco_input_frequency > 2000000)) // skip invalid settings
continue;
for (mul = 64; mul <= 432; mul++) // PLLN in [64; 432]
{
vco_output_frequency = vco_input_frequency * mul;
if ((vco_output_frequency < 64000000ul) || (vco_output_frequency > 432000000ul)) // skip invalid settings
continue;
for (div_core = 2; div_core <= 8; div_core += 2) // PLLP in {2, 4, 6, 8}
{
frequency_core = vco_output_frequency / div_core;
if (frequency_core > CFG_CCLK_FREQ) // skip values over desired frequency
continue;
if (frequency_core > best_frequency_core) // is this configuration better than previous one?
{
best_frequency_core = frequency_core; // yes - save values
best_div = div;
best_mul = mul;
best_div_core = div_core;
}
}
}
}
/* Configure PLL factors, always divide USB clock by 9 */
RCC->PLLCFGR = (best_div << 0) |
(best_mul << 6) |
((best_div_core / 2 - 1) << 16) |
(9 << 24) |
RCC_PLLCFGR_PLLSRC_HSE;
/* AHB - no prescaler, APB1 - divide by 4, APB2 - divide by 2 */
RCC->CFGR = RCC_CFGR_PPRE2_DIV2 |
RCC_CFGR_PPRE1_DIV4 |
RCC_CFGR_HPRE_DIV1;
/* Wait for stable clock */
while (!(RCC->CR & RCC_CR_HSERDY))
;
/* Enable the main PLL */
RCC->CR |= RCC_CR_PLLON;
/* Wait for PLL lock */
while (!(RCC->CR & RCC_CR_PLLRDY))
;
/* Change SYSCLK to PLL */
RCC->CFGR |= RCC_CFGR_SW_PLL;
/* Wait for switch */
while (((RCC->CFGR) & RCC_CFGR_SWS) != RCC_CFGR_SWS_PLL)
;
}