rcc.c

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/** @defgroup rcc_file RCC peripheral API
 *
 * @ingroup peripheral_apis
 *
 * @section rcc_l4_api_ex Reset and Clock Control API.
 *
 * @brief <b>libopencm3 STM32L4xx Reset and Clock Control</b>
 *
 * @author @htmlonly &copy; @endhtmlonly 2016 Karl Palsson <karlp@tweak.net.au>
 *
 * @date 12 Feb 2016
 *
 * This library supports the Reset and Clock Control System in the STM32 series
 * of ARM Cortex Microcontrollers by ST Microelectronics.
 *
 * LGPL License Terms @ref lgpl_license
 */
 
/*
 * This file is part of the libopencm3 project.
 *
 * Copyright (C) 2016 Karl Palsson <karlp@tweak.net.au>
 *
 * This library is free software: you can redistribute it and/or modify
 * it under the terms of the GNU Lesser General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * This library is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public License
 * along with this library.  If not, see <http://www.gnu.org/licenses/>.
 */
 
/**@{*/
#include <libopencm3/cm3/assert.h>
#include <libopencm3/stm32/rcc.h>
#include <libopencm3/stm32/flash.h>
#include <libopencm3/stm32/pwr.h>
 
/* Set the default clock frequencies after reset. */
uint32_t rcc_ahb_frequency = 4000000;
uint32_t rcc_apb1_frequency = 4000000;
uint32_t rcc_apb2_frequency = 4000000;
 
const struct rcc_clock_scale rcc_hsi16_configs[RCC_CLOCK_CONFIG_END] = {
        { /* 80MHz PLL from HSI16 VR1 */
                .pllm = 4,
                .plln = 40,
                .pllp = RCC_PLLCFGR_PLLP_DIV7,
                .pllq = RCC_PLLCFGR_PLLQ_DIV6,
                .pllr = RCC_PLLCFGR_PLLR_DIV2,
                .pll_source = RCC_PLLCFGR_PLLSRC_HSI16,
                .hpre = RCC_CFGR_HPRE_NODIV,
                .ppre1 = RCC_CFGR_PPRE_NODIV,
                .ppre2 = RCC_CFGR_PPRE_NODIV,
                .voltage_scale = PWR_SCALE1,
                .flash_config = FLASH_ACR_DCEN | FLASH_ACR_ICEN |
                FLASH_ACR_LATENCY_4WS,
                .ahb_frequency  = 80000000,
                .apb1_frequency = 80000000,
                .apb2_frequency = 80000000,
        },
};
 
void rcc_osc_ready_int_clear(enum rcc_osc osc)
{
        switch (osc) {
        case RCC_PLL:
                RCC_CICR |= RCC_CICR_PLLRDYC;
                break;
        case RCC_HSE:
                RCC_CICR |= RCC_CICR_HSERDYC;
                break;
        case RCC_HSI16:
                RCC_CICR |= RCC_CICR_HSIRDYC;
                break;
        case RCC_MSI:
                RCC_CICR |= RCC_CICR_MSIRDYC;
                break;
        case RCC_LSE:
                RCC_CICR |= RCC_CICR_LSERDYC;
                break;
        case RCC_LSI:
                RCC_CICR |= RCC_CICR_LSIRDYC;
                break;
        case RCC_HSI48:
                RCC_CICR |= RCC_CICR_HSI48RDYC;
                break;
        }
}
 
void rcc_osc_ready_int_enable(enum rcc_osc osc)
{
        switch (osc) {
        case RCC_PLL:
                RCC_CIER |= RCC_CIER_PLLRDYIE;
                break;
        case RCC_HSE:
                RCC_CIER |= RCC_CIER_HSERDYIE;
                break;
        case RCC_HSI16:
                RCC_CIER |= RCC_CIER_HSIRDYIE;
                break;
        case RCC_MSI:
                RCC_CIER |= RCC_CIER_MSIRDYIE;
                break;
        case RCC_LSE:
                RCC_CIER |= RCC_CIER_LSERDYIE;
                break;
        case RCC_LSI:
                RCC_CIER |= RCC_CIER_LSIRDYIE;
                break;
        case RCC_HSI48:
                RCC_CIER |= RCC_CIER_HSI48RDYIE;
                break;
        }
}
 
void rcc_osc_ready_int_disable(enum rcc_osc osc)
{
        switch (osc) {
        case RCC_PLL:
                RCC_CIER &= ~RCC_CIER_PLLRDYIE;
                break;
        case RCC_HSE:
                RCC_CIER &= ~RCC_CIER_HSERDYIE;
                break;
        case RCC_HSI16:
                RCC_CIER &= ~RCC_CIER_HSIRDYIE;
                break;
        case RCC_MSI:
                RCC_CIER &= ~RCC_CIER_MSIRDYIE;
                break;
        case RCC_LSE:
                RCC_CIER &= ~RCC_CIER_LSERDYIE;
                break;
        case RCC_LSI:
                RCC_CIER &= ~RCC_CIER_LSIRDYIE;
                break;
        case RCC_HSI48:
                RCC_CIER &= ~RCC_CIER_HSI48RDYIE;
                break;
        }
}
 
int rcc_osc_ready_int_flag(enum rcc_osc osc)
{
        switch (osc) {
        case RCC_PLL:
                return ((RCC_CIFR & RCC_CIFR_PLLRDYF) != 0);
                break;
        case RCC_HSE:
                return ((RCC_CIFR & RCC_CIFR_HSERDYF) != 0);
                break;
        case RCC_HSI16:
                return ((RCC_CIFR & RCC_CIFR_HSIRDYF) != 0);
                break;
        case RCC_MSI:
                return ((RCC_CIFR & RCC_CIFR_MSIRDYF) != 0);
                break;
        case RCC_LSE:
                return ((RCC_CIFR & RCC_CIFR_LSERDYF) != 0);
                break;
        case RCC_LSI:
                return ((RCC_CIFR & RCC_CIFR_LSIRDYF) != 0);
                break;
        case RCC_HSI48:
                return ((RCC_CIFR & RCC_CIFR_HSI48RDYF) != 0);
                break;
        }
        return false;
 
}
 
void rcc_css_int_clear(void)
{
        RCC_CICR |= RCC_CICR_CSSC;
}
 
int rcc_css_int_flag(void)
{
        return ((RCC_CIFR & RCC_CIFR_CSSF) != 0);
}
 
bool rcc_is_osc_ready(enum rcc_osc osc)
{
        switch (osc) {
        case RCC_PLL:
                return RCC_CR & RCC_CR_PLLRDY;
        case RCC_HSE:
                return RCC_CR & RCC_CR_HSERDY;
        case RCC_HSI16:
                return RCC_CR & RCC_CR_HSIRDY;
        case RCC_MSI:
                return RCC_CR & RCC_CR_MSIRDY;
        case RCC_LSE:
                return RCC_BDCR & RCC_BDCR_LSERDY;
        case RCC_LSI:
                return RCC_CSR & RCC_CSR_LSIRDY;
        case RCC_HSI48:
                return RCC_CRRCR & RCC_CRRCR_HSI48RDY;
        }
        return false;
}
 
void rcc_wait_for_osc_ready(enum rcc_osc osc)
{
        while (!rcc_is_osc_ready(osc));
}
 
void rcc_wait_for_sysclk_status(enum rcc_osc osc)
{
        switch (osc) {
        case RCC_PLL:
                while (((RCC_CFGR >> RCC_CFGR_SWS_SHIFT) & RCC_CFGR_SWS_MASK)
                        != RCC_CFGR_SWS_PLL);
                break;
        case RCC_HSE:
                while (((RCC_CFGR >> RCC_CFGR_SWS_SHIFT) & RCC_CFGR_SWS_MASK)
                        != RCC_CFGR_SWS_HSE);
                break;
        case RCC_HSI16:
                while (((RCC_CFGR >> RCC_CFGR_SWS_SHIFT) & RCC_CFGR_SWS_MASK)
                        != RCC_CFGR_SWS_HSI16);
                break;
        case RCC_MSI:
                while (((RCC_CFGR >> RCC_CFGR_SWS_SHIFT) & RCC_CFGR_SWS_MASK)
                        != RCC_CFGR_SWS_MSI);
                break;
        default:
                /* Shouldn't be reached. */
                break;
        }
}
 
void rcc_osc_on(enum rcc_osc osc)
{
        switch (osc) {
        case RCC_PLL:
                RCC_CR |= RCC_CR_PLLON;
                break;
        case RCC_HSE:
                RCC_CR |= RCC_CR_HSEON;
                break;
        case RCC_HSI16:
                RCC_CR |= RCC_CR_HSION;
                break;
        case RCC_MSI:
                RCC_CR |= RCC_CR_MSION;
                break;
        case RCC_LSE:
                RCC_BDCR |= RCC_BDCR_LSEON;
                break;
        case RCC_LSI:
                RCC_CSR |= RCC_CSR_LSION;
                break;
        case RCC_HSI48:
                RCC_CRRCR |= RCC_CRRCR_HSI48ON;
                break;
        }
}
 
void rcc_osc_off(enum rcc_osc osc)
{
        switch (osc) {
        case RCC_PLL:
                RCC_CR &= ~RCC_CR_PLLON;
                break;
        case RCC_HSE:
                RCC_CR &= ~RCC_CR_HSEON;
                break;
        case RCC_HSI16:
                RCC_CR &= ~RCC_CR_HSION;
                break;
        case RCC_MSI:
                RCC_CR &= ~RCC_CR_MSION;
                break;
        case RCC_LSE:
                RCC_BDCR &= ~RCC_BDCR_LSEON;
                break;
        case RCC_LSI:
                RCC_CSR &= ~RCC_CSR_LSION;
                break;
        case RCC_HSI48:
                RCC_CRRCR &= ~RCC_CRRCR_HSI48ON;
                break;
        }
}
 
void rcc_css_enable(void)
{
        RCC_CR |= RCC_CR_CSSON;
}
 
void rcc_css_disable(void)
{
        RCC_CR &= ~RCC_CR_CSSON;
}
 
void rcc_set_sysclk_source(uint32_t clk)
{
        uint32_t reg32;
 
        reg32 = RCC_CFGR;
        reg32 &= ~(RCC_CFGR_SW_MASK << RCC_CFGR_SW_SHIFT);
        RCC_CFGR = (reg32 | (clk << RCC_CFGR_SW_SHIFT));
}
 
void rcc_set_pll_source(uint32_t pllsrc)
{
        uint32_t reg32;
 
        reg32 = RCC_PLLCFGR;
        reg32 &= ~(RCC_PLLCFGR_PLLSRC_MASK << RCC_PLLCFGR_PLLSRC_SHIFT);
        RCC_PLLCFGR = (reg32 | (pllsrc << RCC_PLLCFGR_PLLSRC_SHIFT));
}
 
void rcc_set_ppre2(uint32_t ppre2)
{
        uint32_t reg32;
 
        reg32 = RCC_CFGR;
        reg32 &= ~(RCC_CFGR_PPRE2_MASK << RCC_CFGR_PPRE2_SHIFT);
        RCC_CFGR = (reg32 | (ppre2 << RCC_CFGR_PPRE2_SHIFT));
}
 
void rcc_set_ppre1(uint32_t ppre1)
{
        uint32_t reg32;
 
        reg32 = RCC_CFGR;
        reg32 &= ~(RCC_CFGR_PPRE1_MASK << RCC_CFGR_PPRE1_SHIFT);
        RCC_CFGR = (reg32 | (ppre1 << RCC_CFGR_PPRE1_SHIFT));
}
 
void rcc_set_hpre(uint32_t hpre)
{
        uint32_t reg32;
 
        reg32 = RCC_CFGR;
        reg32 &= ~(RCC_CFGR_HPRE_MASK << RCC_CFGR_HPRE_SHIFT);
        RCC_CFGR = (reg32 | (hpre << RCC_CFGR_HPRE_SHIFT));
}
 
void rcc_set_main_pll(uint32_t source, uint32_t pllm, uint32_t plln, uint32_t pllp,
        uint32_t pllq, uint32_t pllr)
{
        RCC_PLLCFGR = (RCC_PLLCFGR_PLLM(pllm) << RCC_PLLCFGR_PLLM_SHIFT) |
                (plln << RCC_PLLCFGR_PLLN_SHIFT) |
                (pllp) |
                (source << RCC_PLLCFGR_PLLSRC_SHIFT) |
                (pllq << RCC_PLLCFGR_PLLQ_SHIFT) |
                (pllr << RCC_PLLCFGR_PLLR_SHIFT) | RCC_PLLCFGR_PLLREN;
}
 
uint32_t rcc_system_clock_source(void)
{
        /* Return the clock source which is used as system clock. */
        return (RCC_CFGR >> RCC_CFGR_SWS_SHIFT) & RCC_CFGR_SWS_MASK;
}
 
/**
 * Setup clocks to run from PLL.
 *
 * The arguments provide the pll source, multipliers, dividers, all that's
 * needed to establish a system clock.
 *
 * @param clock clock information structure.
 */
void rcc_clock_setup_pll(const struct rcc_clock_scale *clock)
{
        /* Enable internal high-speed oscillator (HSI16). */
        rcc_osc_on(RCC_HSI16);
        rcc_wait_for_osc_ready(RCC_HSI16);
 
        /* Select HSI16 as SYSCLK source. */
        rcc_set_sysclk_source(RCC_PLLCFGR_PLLSRC_HSI16);
 
        /* Enable external high-speed oscillator (HSE). */
        if (clock->pll_source == RCC_PLLCFGR_PLLSRC_HSE) {
                rcc_osc_on(RCC_HSE);
                rcc_wait_for_osc_ready(RCC_HSE);
        }
 
        /* Set the VOS scale mode */
        rcc_periph_clock_enable(RCC_PWR);
        pwr_set_vos_scale(clock->voltage_scale);
 
        /*
        * Set prescalers for AHB, ADC, APB1, APB2.
        * Do this before touching the PLL (TODO: why?).
        */
        rcc_set_hpre(clock->hpre);
        rcc_set_ppre1(clock->ppre1);
        rcc_set_ppre2(clock->ppre2);
 
        /* Disable PLL oscillator before changing its configuration. */
        rcc_osc_off(RCC_PLL);
 
        /* Configure the PLL oscillator. */
        rcc_set_main_pll(clock->pll_source, clock->pllm, clock->plln,
                        clock->pllp, clock->pllq,  clock->pllr);
 
        /* Enable PLL oscillator and wait for it to stabilize. */
        rcc_osc_on(RCC_PLL);
        rcc_wait_for_osc_ready(RCC_PLL);
 
        /* Configure flash settings. */
        if (clock->flash_config & FLASH_ACR_DCEN) {
                flash_dcache_enable();
        } else {
                flash_dcache_disable();
        }
        if (clock->flash_config & FLASH_ACR_ICEN) {
                flash_icache_enable();
        } else {
                flash_icache_disable();
        }
        flash_set_ws(clock->flash_config);
 
        /* Select PLL as SYSCLK source. */
        rcc_set_sysclk_source(RCC_CFGR_SW_PLL);
 
        /* Wait for PLL clock to be selected. */
        rcc_wait_for_sysclk_status(RCC_PLL);
 
        /* Set the peripheral clock frequencies used. */
        rcc_ahb_frequency  = clock->ahb_frequency;
        rcc_apb1_frequency = clock->apb1_frequency;
        rcc_apb2_frequency = clock->apb2_frequency;
 
        /* Disable internal high-speed oscillator. */
        if (clock->pll_source == RCC_PLLCFGR_PLLSRC_HSE) {
                rcc_osc_off(RCC_HSI16);
        }
}
 
/**
 * Set the msi run time range.
 * Can only be called when MSI is either OFF, or when MSI is on _and_
 * ready. (RCC_CR_MSIRDY bit).  @sa rcc_set_msi_range_standby
 * @param msi_range range number @ref rcc_cr_msirange
 */
void rcc_set_msi_range(uint32_t msi_range)
{
        uint32_t reg = RCC_CR;
        reg &= ~(RCC_CR_MSIRANGE_MASK << RCC_CR_MSIRANGE_SHIFT);
        reg |= msi_range << RCC_CR_MSIRANGE_SHIFT;
        RCC_CR = reg | RCC_CR_MSIRGSEL;
}
 
/**
 * Set the msi range after reset/standby.
 * Until MSIRGSEl bit is set, this defines the MSI range.
 * Note that not all MSI range values are allowed here!
 * @sa rcc_set_msi_range
 * @param msi_range range number valid for post standby @ref rcc_csr_msirange
 */
void rcc_set_msi_range_standby(uint32_t msi_range)
{
        uint32_t reg = RCC_CSR;
        reg &= ~(RCC_CSR_MSIRANGE_MASK << RCC_CSR_MSIRANGE_SHIFT);
        reg |= msi_range << RCC_CSR_MSIRANGE_SHIFT;
        RCC_CSR = reg;
}
 
/** Enable PLL Output
 *
 *      - P (RCC_PLLCFGR_PLLPEN)
 *      - Q (RCC_PLLCFGR_PLLQEN)
 *      - R (RCC_PLLCFGR_PLLREN)
 *
 * @param pllout One or more of the definitions above
 */
void rcc_pll_output_enable(uint32_t pllout)
{
        RCC_PLLCFGR |= pllout;
}
 
/** Set clock source for 48MHz clock
 *
 * The 48 MHz clock is derived from one of the four following sources:
 *      - main PLL VCO (RCC_CCIPR_CLK48SEL_PLL)
 *      - PLLSAI1 VCO (RCC_CCIPR_CLK48SEL_PLLSAI1Q)
 *      - MSI clock (RCC_CCIPR_CLK48SEL_MSI)
 *      - HSI48 internal oscillator (RCC_CCIPR_CLK48SEL_HSI48)
 *
 * @param clksel One of the definitions above
 */
void rcc_set_clock48_source(uint32_t clksel)
{
        RCC_CCIPR &= ~(RCC_CCIPR_CLK48SEL_MASK << RCC_CCIPR_CLK48SEL_SHIFT);
        RCC_CCIPR |= (clksel << RCC_CCIPR_CLK48SEL_SHIFT);
}
 
 
/** Enable the RTC clock */
void rcc_enable_rtc_clock(void)
{
        RCC_BDCR |= RCC_BDCR_RTCEN;
}
 
/** Disable the RTC clock */
void rcc_disable_rtc_clock(void)
{
        RCC_BDCR &= ~RCC_BDCR_RTCEN;
}
 
/** Set the source for the RTC clock
 * @param[in] clk ::rcc_osc. RTC clock source. Only HSE/32, LSE and LSI.
 */
void rcc_set_rtc_clock_source(enum rcc_osc clk)
{
        RCC_BDCR &= ~(RCC_BDCR_RTCSEL_MASK << RCC_BDCR_RTCSEL_SHIFT);
 
        switch (clk) {
        case RCC_HSE:
                RCC_BDCR |= (RCC_BDCR_RTCSEL_HSEDIV32 << RCC_BDCR_RTCSEL_SHIFT);
                break;
        case RCC_LSE:
                RCC_BDCR |= (RCC_BDCR_RTCSEL_LSE << RCC_BDCR_RTCSEL_SHIFT);
                break;
        case RCC_LSI:
                RCC_BDCR |= (RCC_BDCR_RTCSEL_LSI << RCC_BDCR_RTCSEL_SHIFT);
                break;
        default:
                /* none selected */
                break;
        }
}
 
/* Helper to calculate the frequency of a UART/I2C based on the apb and clksel value.
 * For I2C, clock selection 0b11 is reserved while it specifies LSE for UARTs. */
static uint32_t rcc_uart_i2c_clksel_freq_hz(uint32_t apb_clk, uint8_t shift, uint32_t clock_reg) {
        uint8_t clksel = (clock_reg >> shift) & RCC_CCIPR_USARTxSEL_MASK;
        uint8_t hpre = (RCC_CFGR >> RCC_CFGR_HPRE_SHIFT) & RCC_CFGR_HPRE_MASK;
        switch (clksel) {
                case RCC_CCIPR_USARTxSEL_APB:
                        return apb_clk;
                case RCC_CCIPR_USARTxSEL_SYSCLK:
                        return rcc_ahb_frequency * rcc_get_div_from_hpre(hpre);
                case RCC_CCIPR_USARTxSEL_HSI16:
                        return 16000000U;
                case RCC_CCIPR_USARTxSEL_LSE:
                        return 32768U;
        }
        cm3_assert_not_reached();
}
 
/*---------------------------------------------------------------------------*/
/** @brief Get the peripheral clock speed for the USART at base specified.
 * @param usart  Base address of USART to get clock frequency for.
 */
uint32_t rcc_get_usart_clk_freq(uint32_t usart)
{
        /* Handle values with selectable clocks. */
        if (usart == LPUART1_BASE) {
                return rcc_uart_i2c_clksel_freq_hz(rcc_apb1_frequency, RCC_CCIPR_LPUART1SEL_SHIFT, RCC_CCIPR);
        } else if (usart == USART1_BASE) {
                return rcc_uart_i2c_clksel_freq_hz(rcc_apb2_frequency, RCC_CCIPR_USART1SEL_SHIFT, RCC_CCIPR);
        } else if (usart == USART2_BASE) {
                return rcc_uart_i2c_clksel_freq_hz(rcc_apb1_frequency, RCC_CCIPR_USART2SEL_SHIFT, RCC_CCIPR);
        } else if (usart == USART3_BASE) {
                return rcc_uart_i2c_clksel_freq_hz(rcc_apb1_frequency, RCC_CCIPR_USART3SEL_SHIFT, RCC_CCIPR);
        } else if (usart == UART4_BASE) {
                return rcc_uart_i2c_clksel_freq_hz(rcc_apb1_frequency, RCC_CCIPR_UART4SEL_SHIFT, RCC_CCIPR);
        } else {  /* USART5 */
                return rcc_uart_i2c_clksel_freq_hz(rcc_apb1_frequency, RCC_CCIPR_UART5SEL_SHIFT, RCC_CCIPR);
        }
}
 
/*---------------------------------------------------------------------------*/
/** @brief Get the peripheral clock speed for the Timer at base specified.
 * @param timer  Base address of TIM to get clock frequency for.
 */
uint32_t rcc_get_timer_clk_freq(uint32_t timer)
{
        /* Handle APB1 timers, and apply multiplier if necessary. */
        if (timer == LPTIM1_BASE || timer == LPTIM2_BASE) {
                int shift = (timer == LPTIM1_BASE) ? RCC_CCIPR_LPTIM1SEL_SHIFT : RCC_CCIPR_LPTIM2SEL_SHIFT;
                uint8_t clksel = (RCC_CCIPR >> shift) & RCC_CCIPR_LPTIMxSEL_MASK;
                switch (clksel) {
                        case RCC_CCIPR_LPTIMxSEL_APB:
                                return rcc_apb1_frequency;
                        case RCC_CCIPR_LPTIMxSEL_LSI:
                                return 32000U;
                        case RCC_CCIPR_LPTIMxSEL_HSI16:
                                return 16000000U;
                        case RCC_CCIPR_LPTIMxSEL_LSE:
                                return 32768U;
                }
        } else if (timer >= TIM2_BASE && timer <= TIM7_BASE) {
                uint8_t ppre1 = (RCC_CFGR >> RCC_CFGR_PPRE1_SHIFT) & RCC_CFGR_PPRE1_MASK;
                return (ppre1 == RCC_CFGR_PPRE_NODIV) ? rcc_apb1_frequency
                        : 2 * rcc_apb1_frequency;
        } else {
                uint8_t ppre2 = (RCC_CFGR >> RCC_CFGR_PPRE2_SHIFT) & RCC_CFGR_PPRE2_MASK;
                return (ppre2 == RCC_CFGR_PPRE_NODIV) ? rcc_apb2_frequency
                        : 2 * rcc_apb2_frequency;
        }
        cm3_assert_not_reached();
}
 
/*---------------------------------------------------------------------------*/
/** @brief Get the peripheral clock speed for the I2C device at base specified.
 * @param i2c  Base address of I2C to get clock frequency for.
 */
uint32_t rcc_get_i2c_clk_freq(uint32_t i2c)
{
        if (i2c == I2C1_BASE) {
                return rcc_uart_i2c_clksel_freq_hz(rcc_apb1_frequency, RCC_CCIPR_I2C1SEL_SHIFT, RCC_CCIPR);
        } else if (i2c == I2C2_BASE) {
                return rcc_uart_i2c_clksel_freq_hz(rcc_apb1_frequency, RCC_CCIPR_I2C2SEL_SHIFT, RCC_CCIPR);
        } else if (i2c == I2C3_BASE) {
                return rcc_uart_i2c_clksel_freq_hz(rcc_apb1_frequency, RCC_CCIPR_I2C3SEL_SHIFT, RCC_CCIPR);
        } else {  /* I2C4 */
                return rcc_uart_i2c_clksel_freq_hz(rcc_apb1_frequency, RCC_CCIPR_I2C4SEL_SHIFT, RCC_CCIPR2);
        }
}
 
/*---------------------------------------------------------------------------*/
/** @brief Get the peripheral clock speed for the SPI device at base specified.
 * @param spi  Base address of SPI device to get clock frequency for (e.g. SPI1_BASE).
 */
uint32_t rcc_get_spi_clk_freq(uint32_t spi) {
        if (spi == SPI1_BASE) {
                return rcc_apb2_frequency;
        } else {
                return rcc_apb1_frequency;
        }
}
/**@}*/