text: /****************************************************************************
   * arch/arm/src/stm32l4/stm32l4_pmlpr.c
   *
   *   Copyright (C) 2012, 2017 Gregory Nutt. All rights reserved.
   *   Copyright (C) 2015 Motorola Mobility, LLC. All rights reserved.
   *   Author: Gregory Nutt <gnutt@nuttx.org>
   *
   * Redistribution and use in source and binary forms, with or without
   * modification, are permitted provided that the following conditions
   * are met:
   *
   * 1. Redistributions of source code must retain the above copyright
   *    notice, this list of conditions and the following disclaimer.
   * 2. 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.
   * 3. Neither the name NuttX nor the names of its contributors may be
   *    used to endorse or promote products derived from this software
   *    without specific prior written permission.
   *
   * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
   * "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
   * COPYRIGHT OWNER OR CONTRIBUTORS 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.
   *
   ****************************************************************************/
  
  /****************************************************************************
   * Included Files
   ****************************************************************************/
  
  #include <nuttx/config.h>
  
  #include <stdbool.h>
  
  #include "up_arch.h"
  #include "nvic.h"
  #include "stm32l4_pwr.h"
  #include "stm32l4_pm.h"
  #include "stm32l4_rcc.h"
  
  #if defined(CONFIG_STM32L4_STM32L4X3) || defined(CONFIG_STM32L4_STM32L4X5) || \
      defined(CONFIG_STM32L4_STM32L4X6)
  
  /****************************************************************************
   * Public Functions
   ****************************************************************************/
  
  /****************************************************************************
   * Name: stm32l4_pmlpr
   *
   * Description:
   *   Enter Low-Power Run (LPR) mode.
   *
   * Input Parameters:
   *   None
   *
   * Returned Value:
   *   Zero means that LPR was successfully entered. Otherwise, LPR mode was not
   *   entered and a negated errno value is returned to indicate the cause of the
   *   failure.
   *
   ****************************************************************************/
  
  int stm32l4_pmlpr(void)
  {
    uint32_t regval;
  
    /* Enable MSI clock */
  
    regval  = getreg32(STM32L4_RCC_CR);
    regval |= RCC_CR_MSION;
  
    /* Set MSI clock to 2 MHz */
  
    regval &= ~RCC_CR_MSIRANGE_MASK;
    regval |= RCC_CR_MSIRANGE_2M; /* 2 MHz */
    regval |= RCC_CR_MSIRGSEL;    /* Select new MSIRANGE */
    putreg32(regval, STM32L4_RCC_CR);
  
    /* Select MSI clock as system clock source */
  
    regval  = getreg32(STM32L4_RCC_CFGR);
    regval &= ~RCC_CFGR_SW_MASK;
    regval |= RCC_CFGR_SW_MSI;
    putreg32(regval, STM32L4_RCC_CFGR);
  
    /* Wait until the MSI source is used as the system clock source */
  
    while ((getreg32(STM32L4_RCC_CFGR) & RCC_CFGR_SWS_MASK) != RCC_CFGR_SWS_MSI)
      {
      }
  
    /* Enable Low-Power Run */
  
    regval  = getreg32(STM32L4_PWR_CR1);
    regval |= PWR_CR1_LPR;
    putreg32(regval, STM32L4_PWR_CR1);
  
    return OK;
  }
  
  #endif /* CONFIG_STM32L4_STM32L4X3 || CONFIG_STM32L4_STM32L4X5 || CONFIG_STM32L4_STM32L4X6 */
  