Datasheet

Clocking
Intel
®
Quark™ microcontroller D2000
January 2016 Datasheet
Document Number: 333577-002EN 59
• Bypass mode allows an external clock (fed through RTC_XTALI pin) to be
provided through the RTC oscillator. To achieve this, OSC1_BYP_XTAL_UP=1
and OSC1_PD=0)
• 600mS start-up time to reach +/-20ppm
The Intel
®
Quark™ microcontroller D2000 is designed to operate without RTC clock as
well, if platform does not require RTC clock. RTC clock is needed for any of the
following reasons:
• Periodic waking in low power sleep state.
• Real Time Clock
• GPIO based wake (input debouncing/filter)
If above reasons are not required in a platform, then RTC oscillator can be disabled
without connecting RTC XTAL on board. In this mode, only comparator based wake
can be enabled to exit low power state.
7.2.3 Root Clock Frequency Scaling
The Intel
®
Quark™ microcontroller D2000 supports a single root clock with multiple
supported root clock frequencies
1) 32MHz high accuracy Crystal Oscillator – required for high accuracy
applications.
2) 4/8/16/32MHz silicon Oscillator – A lower power operating mode used by
applications that do not require a high frequency accuracy.
3) 32.768 kHz - entire SoC can operate out of 32.768 kHz clock as system clock
(controlled by CCU_SYS_CLK_SEL register in SCSS) without enabling Hybrid
Oscillator for such applications that require ultra low power without much
compute performance.
7.2.4 Frequency Scaling
The Intel
®
Quark™ microcontroller D2000 supports a wide range of frequency scaling
options to optimize power.
1) The root system clock frequency can be scaled to 4/8/16/32MHz
2) The Leaf peripheral clock can be independently scaled @ /2 /4 /8 divisions
To apply a DFS setting the following procedure should be followed
1) Apply the clock divider value CCU_XXX_CLK_DIV
2) Apply the clock divider writing ‘0’ CCU_XXX_CLK_DIV_EN
3) Apply the clock divider writing ‘1’ CCU_XXX_CLK_DIV_EN
7.2.4.1 Peripheral DFS requirements
When using DFS it is the responsibility of firmware to adjust any settings in
peripheral/timers to account for the frequency change. Example to achieve a UART
baud rate of 115200 requires a different baud rate divider depending on the
frequency.