Power Management
15-49
Clock Generation and System Reset Management
are actually a few extra cycles after the MPU_RST pin is deasserted high for
synchronization before the cycle count starts.
Note:
The FLASH.RP signal is low when either PWRON_RESET or MPU_RST is
low, and it stays low for an additional ~8 CLKINs after PWRON_RESET and
MPU_RST are released.
In addition, FLASH.RP goes low if the TC is in IDLE mode and
ARM_EWUPCT REPWR_EN field = 0.
15.3.11
Configuring Clocks After a Reset
After a reset, the device is in the fully synchronous clocking mode. DPLL1 is
selected as the source for CLK_GEN1, CLK_GEN2, and CLK_GEN3. The
DPLL1 is disabled, so the device is running at the CK_REF frequency. Set the
domains to operate at the desired frequencies as follows:
-
Select the desired clocking mode via the CLOCK_SELECT bit of the MPU
system status register (ARM_SYSST).
-
Program each of the division modes for the DPLLs for the clock domains.
-
Program the DPLLs and enable them.
-
Program each domain-defined enable bit (discussed in section 15.4,
Clock Generation and Reset Control Registers). Some peripherals have
additional enables for their local clocks (discussed in various peripheral
chapters).
After a reset, the application software can write to the control registers via
CLOCK_SELECT (2:0) bits of the MPU system status register (ARM_SYSST)
to switch to a desired mode of operation. However, use the system software
to save the context before switching modes. For information about the switch-
ing procedure, see Appendix B, Switching Clock Modes.