Datasheet

and a one in the HAD_PSM_RESTART field indicates the chip has been reset via Rescue Debug Port. There should never be
more than one field set to one.
2.12.8. List of Registers
The chip-level reset subsystem shares a register address space with the on-chip voltage regulator. The registers for
both subsystems are listed in Section 2.10.6. The shared address space is referred to as vreg_and_chip_reset elsewhere
in this document.
2.13. Power-On State Machine
2.13.1. Overview
The power-on state machine removes the reset from various hardware blocks in a specific order. Each peripheral in the
power-on state machine is controlled by an internal rst_n active-low reset signal and generates an internal rst_done
active-high reset done signal. The power-on state machine deasserts the reset to each peripheral, waits for that
peripheral to assert its rst_done and then deasserts the reset to the next peripheral. An important use of this is to wait
for a clock source to be running cleanly in the chip before the reset to the clock generators is deasserted. This avoids
potentially glitchy clocks being distributed to the chip.
The power-on state machine is itself taken out of reset when the Chip-Level Reset subsystem confirms that the digital
core supply (DVDD) is powered and stable, and the RUN pin is high. The power-on state machine takes a number of other
blocks out of reset at this point via its rst_n_run output. This is used to reset things that need to be reset at start-up but
must not be reset if the power-on state machine is restarted. This list includes:
•
Power on logic in the ring oscillator and crystal oscillator
•
Clock dividers which must keep on running during a power-on state machine restart (clk_ref and clk_sys)
•
Watchdog (contains scratch registers which need to persist through a soft-restart of the power-on state machine)
2.13.2. Power On Sequence
Chip Level Reset
Released
Clock GeneratorsRing Oscillator
XIP
(Execute-In-Place)
ROM / SRAM Bus Fabric
Crystal Oscillator Reset Controller
Chip Level Reset
and Voltage
Regulator Registers
Processor Complex
Figure 27. Power-On
State Machine
Sequence.
The power-on state machine sequence is as follows:
•
Chip-Level Reset subsystem deasserts power-on state machine reset once digital core supply (DVDD) is powered
and stable, and RUN pin is high (rst_n_run is also deasserted at this point)
•
Ring Oscillator is started. rst_done is asserted once the ripple counter has seen a sufficient number of clock edges
to indicate the ring oscillator is stable
RP2040 Datasheet
2.13. Power-On State Machine 195