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cc2538: lpm: Speed up the transition to the 32-MHz XOSC after wake-up

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As recommended by the CC2538 User's Guide, set SYS_CTRL_CLOCK_CTRL.OSC_PD to 0
before asserting WFI, and set it to 1 after the system clock is sourced from the
32-MHz XOSC following wake-up. This allows to automatically start both
oscillators upon wake-up in order to partially hide the 32-MHz XOSC startup time
by the 16-MHz RCOSC startup time.

Signed-off-by: Benoît Thébaudeau <benoit.thebaudeau@advansee.com>
This commit is contained in:
Benoît Thébaudeau 2013-12-03 19:03:00 +01:00
parent 13006e1c73
commit f149197aa8
1 changed files with 9 additions and 0 deletions
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9
cpu/cc2538/lpm.c
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@ -166,11 +166,20 @@ select_32_mhz_xosc(void)
/* Wait for the switch to take place */
while((REG(SYS_CTRL_CLOCK_STA) & SYS_CTRL_CLOCK_STA_OSC) != 0);
/* Power down the unused oscillator. */
REG(SYS_CTRL_CLOCK_CTRL) |= SYS_CTRL_CLOCK_CTRL_OSC_PD;
}
/*---------------------------------------------------------------------------*/
static void
select_16_mhz_rcosc(void)
{
/*
* Power up both oscillators in order to speed up the transition to the 32-MHz
* XOSC after wake up.
*/
REG(SYS_CTRL_CLOCK_CTRL) &= ~SYS_CTRL_CLOCK_CTRL_OSC_PD;
/*First, make sure there is no ongoing clock source change */
while((REG(SYS_CTRL_CLOCK_STA) & SYS_CTRL_CLOCK_STA_SOURCE_CHANGE) != 0);