/***************************************************************************//**
* @brief
* Restore oscillators and core clock after having been in EM2 or EM3.
******************************************************************************/
static void EMU_Restore(void)
{
uint32_t cmuLocked;
/* Although we could use the CMU API for most of the below handling, we */
/* would like this function to be as efficient as possible. */
/* CMU registers may be locked */
cmuLocked = CMU->LOCK & CMU_LOCK_LOCKKEY_LOCKED;
CMU_Unlock();
/* AUXHFRCO was automatically disabled (except if using debugger). */
/* HFXO was automatically disabled. */
/* LFRCO/LFXO were possibly disabled by SW in EM3. */
/* Restore according to status prior to entering EM. */
CMU->OSCENCMD = cmuStatus & (CMU_STATUS_AUXHFRCOENS |
CMU_STATUS_HFXOENS |
CMU_STATUS_LFRCOENS |
CMU_STATUS_LFXOENS);
/* Restore oscillator used for clocking core */
switch (cmuStatus & (CMU_STATUS_HFXOSEL | CMU_STATUS_HFRCOSEL |
CMU_STATUS_LFXOSEL | CMU_STATUS_LFRCOSEL))
{
case CMU_STATUS_LFRCOSEL:
/* Wait for LFRCO to stabilize */
while (!(CMU->STATUS & CMU_STATUS_LFRCORDY)) ;
CMU->CMD = CMU_CMD_HFCLKSEL_LFRCO;
break;
case CMU_STATUS_LFXOSEL:
/* Wait for LFXO to stabilize */
while (!(CMU->STATUS & CMU_STATUS_LFXORDY)) ;
CMU->CMD = CMU_CMD_HFCLKSEL_LFXO;
break;
case CMU_STATUS_HFXOSEL:
/* Wait for HFXO to stabilize */
while (!(CMU->STATUS & CMU_STATUS_HFXORDY)) ;
CMU->CMD = CMU_CMD_HFCLKSEL_HFXO;
break;
default: /* CMU_STATUS_HFRCOSEL */
/* If core clock was HFRCO core clock, it is automatically restored to */
/* state prior to entering energy mode. No need for further action. */
break;
}
/* Restore CMU register locking */
if (cmuLocked)
{
CMU_Lock();
}
}
/***************************************************************************//**
* @brief
* Enter energy mode 3 (EM3).
*
* @details
* When entering EM3, the high frequency clocks are disabled by HW, ie HFXO,
* HFRCO and AUXHFRCO (for AUXHFRCO, see exception note below). In addition,
* the low frequency clocks, ie LFXO and LFRCO are disabled by SW. When
* re-entering EM0, HFRCO is re-enabled and the core will be clocked by the
* configured HFRCO band. This ensures a quick wakeup from EM3.
*
* However, prior to entering EM3, the core may have been using another
* oscillator than HFRCO. The @p restore parameter gives the user the option
* to restore all HF/LF oscillators according to state prior to entering EM3,
* as well as the clock used to clock the core. This restore procedure is
* handled by SW. However, since handled by SW, it will not be restored
* before completing the interrupt function(s) waking up the core!
*
* @note
* If restoring core clock to use an oscillator other than HFRCO, this
* function will stall until the oscillator has stabilized. Stalling time
* can be reduced by adding interrupt support detecting stable oscillator,
* and an asynchronous switch to the original oscillator. See CMU
* documentation. Such a feature is however outside the scope of the
* implementation in this function.
* @par
* If HFXO/LFXO/LFRCO are re-enabled by this function, and NOT used to clock
* the core, this function will not wait for those oscillators to stabilize.
* This must be considered by the application if trying to use features
* relying on those oscillators upon return.
* @par
* If a debugger is attached, the AUXHFRCO will not be disabled if enabled
* upon entering EM3. It will thus remain enabled when returning to EM0
* regardless of the @p restore parameter.
*
* @param[in] restore
* @li true - restore oscillators and clocks, see function details.
* @li false - do not restore oscillators and clocks, see function details.
* @par
* The @p restore option should only be used if all clock control is done
* via the CMU API.
******************************************************************************/
void EMU_EnterEM3(bool restore)
{
uint32_t cmuLocked;
/* Auto-update CMU status just in case before entering energy mode. */
/* This variable is normally kept up-to-date by the CMU API. */
cmuStatus = (uint16_t)(CMU->STATUS);
/* CMU registers may be locked */
cmuLocked = CMU->LOCK & CMU_LOCK_LOCKKEY_LOCKED;
CMU_Unlock();
/* Disable LF oscillators */
CMU->OSCENCMD = CMU_OSCENCMD_LFXODIS | CMU_OSCENCMD_LFRCODIS;
/* Restore CMU register locking */
if (cmuLocked)
{
CMU_Lock();
}
/* Enter Cortex-M3 deep sleep mode */
SCB->SCR |= SCB_SCR_SLEEPDEEP_Msk;
__WFI();
/* Restore oscillators/clocks if specified */
if (restore)
{
EMU_Restore();
}
/* If not restoring, and original clock was not HFRCO, we have to */
/* update CMSIS core clock variable since core clock has changed */
/* to using HFRCO. */
else if (!(cmuStatus & CMU_STATUS_HFRCOSEL))
{
SystemCoreClockUpdate();
}
}
