Power, Reset, and Clock Management
The ADPLLLJ module supports two different bypass modes via their internal MNBypass mode and their
external Low Power Idle bypass mode. The PLLs are in the MNBypass mode after power-on reset and
can be configured by software to enter Low Power Idle bypass mode for power-down.
The PER PLL can use the Low Power Idle bypass mode. When the internal bypass mode is selected, the
CLKOUT output is driven by CLKINP/(N2+1) where N2 is driven by the PRCM. CLKINP defaults to the
master oscillator input (typically 24 MHz)
8.1.6.8.1 Configuring the Peripheral PLL
The following steps detail how to configure the peripheral PLL.
1. Switch PLL to bypass mode by setting CM_CLKMODE_DPLL_PER.DPLL_EN to 0x4.
2. Wait for CM_IDLEST_DPLL_PER.ST_MN_BYPASS = 1 to ensure PLL is in bypass
(CM_IDLEST_DPLL_PER.ST_DPLL_CLK should also change to 0 to denote the PLL is unlocked).
3. Configure Multiply and Divide values by setting CM_CLKSEL_DPLL_PER.DPLL_MULT and DPLL_DIV
to the desired values.
4. Configure M2 divider by setting CM_DIV_M2_DPLL_PER.DPLL_CLKOUT_DIV to the desired value.
5. Switch over to lock mode by setting CM_CLKMODE_DPLL_PER.DPLL_EN to 0x7.
6. Wait for CM_IDLEST_DPLL_PER.ST_DPLL_CLK = 1 to ensure PLL is locked
(CM_IDLEST_DPLL_PER.ST_MN_BYPASS should also change to 0 to denote the PLL is out of
bypass mode).
Note: M2 divider can also be changed on-the-fly (ie., there is no need to put the PLL in bypass and back
to lock mode). After changing CM_DIV_M2_DPLL_PER.DPLL_CLKOUT_DIV, check
CM_DIV_M2_DPLL_PER.DPLL_CLKOUT_DIVCHACK for a toggle (a change from 0 to 1 or 1 to 0) to see
if the change was acknowledged by the PLL.
8.1.6.9
MPU PLL Description
The Cortex A8 MPU subsystem includes an internal ADPLLS for generating the required Cortex A8 MPU
clocks. This PLL is driven by the master oscillator output with control provided by PRCM registers.
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SPRUH73H – October 2011 – Revised April 2013
Power, Reset, and Clock Management (PRCM)
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