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/*
* Copyright (C) 2014 Freie Universität Berlin
*
* This file is subject to the terms and conditions of the GNU Lesser General
* Public License v2.1. See the file LICENSE in the top level directory for more
* details.
*/
/**
* @ingroup cpu_stm32f4
* @{
*
* @file
* @brief Implementation of the CPU initialization
*
* @author Hauke Petersen <hauke.petersen@fu-berlin.de>
* @}
*/
#include <stdint.h>
#include "cpu.h"
#include "periph_conf.h"
/**
* @name Pattern to write into the Coprocessor Access Control Register to allow full FPU access
*/
#define FULL_FPU_ACCESS (0x00f00000)
static void cpu_clock_init(void);
/**
* @brief Initialize the CPU, set IRQ priorities
*/
void cpu_init(void)
{
/* give full access to the FPU */
SCB->CPACR |= (uint32_t)FULL_FPU_ACCESS;
/* configure the vector table location to internal flash */
SCB->VTOR = FLASH_BASE;
/* initialize the clock system */
cpu_clock_init();
/* set pendSV interrupt to lowest possible priority */
NVIC_SetPriority(PendSV_IRQn, 0xff);
}
/**
* @brief Configure the controllers clock system
*
* The clock initialization make the following assumptions:
* - the external HSE clock from an external oscillator is used as base clock
* - the internal PLL circuit is used for clock refinement
*
* Use the following formulas to calculate the needed values:
*
* SYSCLK = ((HSE_VALUE / CLOCK_PLL_M) * CLOCK_PLL_N) / CLOCK_PLL_P
* USB, SDIO and RNG Clock = ((HSE_VALUE / CLOCK_PLL_M) * CLOCK_PLL_N) / CLOCK_PLL_Q
*
* The actual used values are specified in the board's `periph_conf.h` file.
*
* NOTE: currently there is not timeout for initialization of PLL and other locks
* -> when wrong values are chosen, the initialization could stall
*/
static void cpu_clock_init(void)
{
/* configure the HSE clock */
/* enable the HSI clock */
RCC->CR |= RCC_CR_HSION;
/* reset clock configuration register */
RCC->CFGR = 0;
/* disable HSE, CSS and PLL */
RCC->CR &= ~(RCC_CR_HSEON | RCC_CR_HSEBYP | RCC_CR_CSSON | RCC_CR_PLLON);
/* disable all clock interrupts */
RCC->CIR = 0;
/* enable the HSE clock */
RCC->CR |= RCC_CR_HSEON;
/* wait for HSE to be ready */
while (!(RCC->CR & RCC_CR_HSERDY));
/* setup power module */
/* enable the power module */
RCC->APB1ENR |= RCC_APB1ENR_PWREN;
/* set the voltage scaling to 1 to enable the maximum frequency */
PWR->CR |= PWR_CR_VOS_1;
/* setup the peripheral bus prescalers */
/* set the AHB clock divider */
RCC->CFGR &= ~RCC_CFGR_HPRE;
RCC->CFGR |= CLOCK_AHB_DIV;
/* set the APB2 (high speed) bus clock divider */
RCC->CFGR &= ~RCC_CFGR_PPRE2;
RCC->CFGR |= CLOCK_APB2_DIV;
/* set the APB1 (low speed) bus clock divider */
RCC->CFGR &= ~RCC_CFGR_PPRE1;
RCC->CFGR |= CLOCK_APB1_DIV;
/* configure the PLL */
/* reset PLL config register */
RCC->PLLCFGR = 0;
/* set HSE as source for the PLL */
RCC->PLLCFGR |= RCC_PLLCFGR_PLLSRC_HSE;
/* set division factor for main PLL input clock */
RCC->PLLCFGR |= (CLOCK_PLL_M & 0x3F);
/* set main PLL multiplication factor for VCO */
RCC->PLLCFGR |= (CLOCK_PLL_N & 0x1FF) << 6;
/* set main PLL division factor for main system clock */
RCC->PLLCFGR |= (((CLOCK_PLL_P & 0x03) >> 1) - 1) << 16;
/* set main PLL division factor for USB OTG FS, SDIO and RNG clocks */
RCC->PLLCFGR |= (CLOCK_PLL_Q & 0x0F) << 24;
/* enable PLL again */
RCC->CR |= RCC_CR_PLLON;
/* wait until PLL is stable */
while(!(RCC->CR & RCC_CR_PLLRDY));
/* configure flash latency */
/* reset flash access control register */
FLASH->ACR = 0;
/* enable instruction cache */
FLASH->ACR |= FLASH_ACR_ICEN;
/* enable data cache */
FLASH->ACR |= FLASH_ACR_DCEN;
/* enable pre-fetch buffer */
// FLASH->ACR |= FLASH_ACR_PRFTEN;
/* set flash latency */
FLASH->ACR &= ~FLASH_ACR_LATENCY;
FLASH->ACR |= CLOCK_FLASH_LATENCY;
/* configure the sysclock and the peripheral clocks */
/* set sysclock to be driven by the PLL clock */
RCC->CFGR &= ~RCC_CFGR_SW;
RCC->CFGR |= RCC_CFGR_SW_PLL;
/* wait for sysclock to be stable */
while (!(RCC->CFGR & RCC_CFGR_SWS_PLL));
}