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Lecture 3
Power, Reset, and Clock Management
NCHUEE 720A Lab
Prof. Jichiang Tsai
Device Power-Management Architecture
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Ensures maximum performance and operation time for
user satisfaction
Offers versatile power-management techniques for
maximum design flexibility
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Built with three levels of resource management
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Clock, power, and voltage management
Enforced by defining the clock, power, and voltage domains
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A group of modules or subsections share a common entity, e.g., common
clock source, common voltage source, or common power switch
The group is managed by a policy manager, e.g., a clock for a clock domain
is managed by a dedicated clock manager within the power, reset, and
clock management (PRCM) module
The clock manager considers the joint clocking constraints of all the
modules receiving that clock
NCHUEE 720A Lab
Prof. Jichiang Tsai
PRCM Module Overview
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Supports an enhanced power management scheme based
on four functional power domains
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WAKEUP, MPU, PER, and RTC
Features:
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Software configurable for direct, automatic, or a combination
thereof, functional power domain state transition control
Device power-up sequence control
Device sleep/wake-up sequence control
Centralized reset generation and management
Centralized clock generation and management
NCHUEE 720A Lab
Prof. Jichiang Tsai
Clock Management
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The PRCM module along with the control module
manages the gating and enabling of the clocks of modules
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The clocks are managed based on the requirement constraints
of the associated modules
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Each module has specific clock input characteristic requirements
Based on the characteristics, the clocks are divided into
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Interface clocks and functional clocks
NCHUEE 720A Lab
Prof. Jichiang Tsai
Clock Management (cont.)
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The interface clocks have the characteristics
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Ensure proper communication between any module/subsystem
and interconnect
In most cases, supply the system interconnect interface and
registers of the module
A typical module has one interface clock
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Modules with multiple interface clocks may also exist
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When connected to multiple interconnect buses
Interface clock management is done at the device level
An interface clock is identified by an _ICLK suffix
Functional clocks have the characteristics
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Supply the functional part of a module or subsystem
NCHUEE 720A Lab
Prof. Jichiang Tsai
Clock Management (cont.)
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A module can have one or more functional clocks
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Some functional clocks are mandatory,
Others are optional
A module needs its mandatory clock(s) to be operational.
The optional clocks are used for specific features
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A functional clock is distributed directly to the related modules
through a dedicated clock tree
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Can be shut down without stopping the module activity
Identified with an _FCLK suffix
Each module may also have specific clock requirements
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Certain module clocks must be active when operating in
specific modes, or may be gated otherwise
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The activation and gating of clocks are managed by the PRCM module
NCHUEE 720A Lab
Prof. Jichiang Tsai
Clock Management (cont.)
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The PRCM module must be aware of when to activate and when to gate
the module clocks
The PRCM module differentiates the clock-management
behavior based on
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Whether the module can initiate transactions on the device
interconnect (master module or initiators)
Or cannot initiate transactions and only responds to the
transactions initiated by the master (slave module or targets)
Two hardware-based power-management protocols are used
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Master standby protocol: Clock-management protocol between the
PRCM and master modules
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A master module must initiate a transaction on the device interconnect
and requests specific (functional and interface) clocks for the purpose
NCHUEE 720A Lab
Prof. Jichiang Tsai
Clock Management (cont.)
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The PRCM module ensures that the required clocks are active when the
master module requests the PRCM module to enable them
Called a module wake-up transition
The module is said to be functional after this transition completes
When the master module no longer requires the clocks, it informs the
PRCM module, which can then gate the clocks to the module
The master module is then said to be in standby mode
Slave idle protocol: Clock-management protocol between the PRCM
and slave modules
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Allows the PRCM module to control the state of a slave module
The PRCM module informs the slave module, through assertion of an idle
request, when its clocks (interface and functional) can be gated.
The slave can then acknowledge the request from the PRCM module
The PRCM module is then allowed to gate the clocks to the module
A slave module is said to be in IDLE state when its clocks are gated by the
PRCM module
NCHUEE 720A Lab
Prof. Jichiang Tsai
Clock Management (cont.)
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Both protocols are completely hardware-controlled
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An idled slave module may need to be wakened because of a service
request from a master module or as a result of an event received by the
slave module (called a wake-up event; e.g., interrupt or DMA request)
The PRCM module enables the clocks to the module and then deasserts
the idle request to signal the module to wake up
But software must configure the clock-management behavior for the
master or slave modules
PRCM offers also the possibility to manage optional
clocks, through a direct SW control
NCHUEE 720A Lab
Prof. Jichiang Tsai
Clock Domain
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A group of modules fed by clock signals controlled by the
same clock manager in the PRCM module
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By gating the clocks in a clock domain, the clocks to all the
modules of that domain can be cut
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To lower their active power consumption
The device is on and the clocks to the modules are dynamically
switched to ACTIVE or INACTIVE (GATED) states
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A clock domain allows control of the dynamic power consumption
The device is partitioned into multiple clock domains
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Each clock domain is controlled by an associated clock
manager within the PRCM module
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Allows the PRCM module to individually activate and gate each clock
domain of the device
NCHUEE 720A Lab
Prof. Jichiang Tsai
Clock Domain (cont.)
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Two clock managers: CM_a and CM_b
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The clock domain of CM_b is composed of two clocks
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A functional clock (FCLK2) and an interface clock (ICLK1)
The clock domain of CM_a consists of a clock (CLK1)
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Used by the module as a functional and interface clock
NCHUEE 720A Lab
Prof. Jichiang Tsai
Clock Domain (cont.)
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The clocks to Module 2 can be gated independently of the
clock to Module 1
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Ensuring power savings when Module 2 is not in use
The PRCM module lets software check the status of the clock
domain functional clocks: Active or Gated
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The CM_<Clock domain>_CLKSTCTRL[x]
CLKACTIVITY_<FCLK/Clock name_FCLK> bit in the PRCM module
identifies the state of the functional clock(s) within the clock domain
NCHUEE 720A Lab
Prof. Jichiang Tsai
Clock Domain (cont.)
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The domain clock manager can automatically and jointly
manage the interface clocks within the clock domain
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The former is based on hardware conditions
The functional clocks within the clock domain are
managed through software settings
A clock domain can switch between three possible states
NCHUEE 720A Lab
Prof. Jichiang Tsai
Clock Domain (cont.)
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ACTIVE
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IDLE_TRANSITION
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Every nondisabled slave module is put out of IDLE state
All interface clocks to the nondisabled slave modules are provided
All functional and interface clocks to the active master are provided
All enabled optional clocks to the modules are provided
This is a transitory state
Every master module is in STANDBY state
Every idle request to all the slave modules is asserted
The functional clocks to the slave module in enabled remain active
All enabled optional clocks to the modules are provided
INACTIVE
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All clocks within the clock domain are gated
NCHUEE 720A Lab
Prof. Jichiang Tsai
Clock Domain (cont.)
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Every slave module is in IDLE state and set to disabled
Every optional functional clock is gated
Each clock domain transition behavior is managed by an
associated register bit field in the CM_<Clock
domain>_CLKSTCTRL[x] CLKTRCTRL PRCM module
NCHUEE 720A Lab
Prof. Jichiang Tsai
Power Management
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The PRCM module manages the switching on and off of
the power supply to the device modules
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To minimize device power consumption, the power to the
modules can be switched off when they are not in use
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Independent power control of sections allows PRCM to turn on and
off specific sections without affecting the others
A power domain is a section device with an independent and
dedicated power manager
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To minimize power consumption, the modules are grouped
A power domain can be split into a logic area and a memory area
The power manager is assigned the task of managing the domain
power transitions
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It ensures that all hardware conditions are satisfied before it can initiate a
power domain transition from a source to a target power state
NCHUEE 720A Lab
Prof. Jichiang Tsai
Power Management (cont.)
NCHUEE 720A Lab
Prof. Jichiang Tsai
Power Management (cont.)
NCHUEE 720A Lab
Prof. Jichiang Tsai
Power Modes
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In order of the lowest power to the highest power
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RTC-Only, DeepSleep0, DeepSleep1, DeepSleep2, Standby and
Active
All voltage supplies must be maintained for the each of the
Deep Sleep, Standby and Active modes
The contents of SDRAM are preserved in any of the Deep
Sleep/Standby modes
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By placing SDRAM in self-refresh prior to entering Deep Sleep
Active
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The supply to all voltage rails must be maintained
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All power domains come up in ON state
The device is fully functional
NCHUEE 720A Lab
Prof. Jichiang Tsai
Power Modes (cont.)
NCHUEE 720A Lab
Prof. Jichiang Tsai
Power Modes (cont.)
NCHUEE 720A Lab
Prof. Jichiang Tsai
Power Modes (cont.)
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Standby
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The supply to all voltage rails must be maintained
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The power consumption can be minimized if the supply voltage placed
at its minimum operating voltage
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Using Software, the required PLL’s are made active depending upon
wakeup or use case requirements
The rest are placed in low power bypass modes
All non-essential IP blocks are powered down
SDRAM contents are preserved
This is useful for quick standby/resume kind of application
DeepSleep0
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The supply to all voltage rails are maintained
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Only the PD_RTC and PD_WKUP power domains are ON
NCHUEE 720A Lab
Prof. Jichiang Tsai
Power Modes (cont.)
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The master crystal oscillator is disabled
The contents of OCMC RAM are preserved
The contents of the SDRAM are preserved by placing the
SDRAM in self-refresh
Activity on wake up peripherals via wake up events enables the
master crystal oscillator using the oscillator control circuit
Deepsleep1
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The supply to all voltage rails are maintained
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The PD_RTC, PD_WKUP & PD_PER power domains are ON
The PD_GFX power domain is OFF
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But could be optionally ON at the cost of more power
The master crystal oscillator is disabled
The contents of internal SRAM are preserved
NCHUEE 720A Lab
Prof. Jichiang Tsai
Power Modes (cont.)
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The contents of the SDRAM are preserved by placing the
SDRAM in self-refresh
Activity on wake up peripherals via wake up events enables the
master crystal oscillator using the oscillator control circuit
Deepsleep2
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The supply to all voltage rails are maintained
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All power domains are ON
The PD_GFX power domain is OFF
The master crystal oscillator is disabled
The contents of internal SRAM are preserved
The contents of the SDRAM are preserved by placing the
SDRAM in self-refresh
NCHUEE 720A Lab
Prof. Jichiang Tsai
Power Modes (cont.)
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Activity on wake up peripherals via wake events enables the
master crystal oscillator using the oscillator control circuit
RTC-Only
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Only the supplies to the RTC subsystem are supplied
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Only the RTC power supply is expected to be ON
All the remaining supplies are expected to be OFF.
For SDRAM to be in self-refresh during this mode, the CKE pin
of the DDR interface needs to have a pulldown on the board
Wakeup Sources/Events
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Events will wake up the device from Deep sleep modes
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These are part of the Wakeup Power domain and remain always ON
GPIO0 bank
NCHUEE 720A Lab
Prof. Jichiang Tsai
Power Modes (cont.)
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dmtimer1_1ms (timer based wakeup)
USB2PHY (USB resume signaling from suspend)
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TSC (Touch screen controller), ADC monitor functions
UART0 (Infra-red support), I2C0
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Both USB ports supported
These events apply on any of the deep sleep and standby modes
Wakeup Sequencing
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The wake up event will switch on the oscillator
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If it was configured to go OFF during sleep
Cortex A8 MPU starts executing from ROM reset vector
Restore the application context
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Only for Deep sleep 0
NCHUEE 720A Lab
Prof. Jichiang Tsai
Reset Management
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The PRCM manages the resets to all power domains and
generation of a single reset output signal
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The PRCM has no knowledge of or control over resets
generated locally within a module
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All PRM reset outputs are asynchronously asserted
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e.g., via the OCP configuration register bit
IPName_SYSCONFIG.SoftReset
These outputs are active-low except for the PLL resets
Through device pin, PWRONRSTn, for external use
Deassertion is synchronous to a clock
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The clock runs a counter used to stall, or delay, reset deassertion
upon source deactivation
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This clock will be CLK_M_OSC used by all the reset managers
NCHUEE 720A Lab
Prof. Jichiang Tsai
Reset Management (cont.)
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All modules receiving a PRCM generated reset are expected to
treat the reset as asynchronous
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One or more Reset Managers are required per power domain
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Implement local re-synchronization upon de-activation as needed
Independent management of multiple reset domains is required to
meet the reset sequencing requirements of all modules
The PRCM collects many sources of reset
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Cold reset: it affects all the logic in a given entity
Warm reset: it is a partial reset
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It does not affect all the logic in a given entity
Global reset: it affects the entire device
Local reset: it affects part of the device
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e.g., One power domain
NCHUEE 720A Lab
Prof. Jichiang Tsai
Reset Management (cont.)
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S/W reset: it is initiated by software
H/W reset: it is hardware driven
Each reset source is specified as being a cold or warm type
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Cold types are applied globally within each receiving entity
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i.e., sub-system, module, macro-cell
Synonymous with power-on-reset (POR) types
Cold reset events include: device power-up, power-domain power-up, and
eFuse programming failures
Warm types are not necessarily applied globally within each entity
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A module may use a warm reset to reset a subset of its logic
To speed-up reset recovery time, i.e., the time to transition to a safe
operating state, compared to the time required by a cold reset
Warm reset events include: software initiated per power-domain, watchdog time-out, externally triggered, and emulation initiated
NCHUEE 720A Lab
Prof. Jichiang Tsai
Reset Management (cont.)
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Reset sources, warm or cold types, intended for device-wide
effect are classified as global sources
Reset sources intended for regional effect are classified as local
sources
Each Reset Manager provides two reset outputs
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A cold reset generated from the group of global and local cold
reset sources it receives
A warm+cold reset generated from the combined groups of,
global and local, cold and warm reset sources it receives
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The Reset Manager asserts one, or both, of its reset outputs
asynchronously upon reset source assertion
Reset deassertion is extended beyond the time the source gets
deasserted
NCHUEE 720A Lab
Prof. Jichiang Tsai
Reset Management (cont.)
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The reset manager will extend the active period of the reset outputs
beyond the release of the reset source, according to the PRCM’s internal
constraints and device’s constraints
Some reset durations can be software-configured
Most (but not all) reset sources are logged by PRCM’s
reset status registers
The same reset output can generally be activated by
several reset sources
The same reset source can generally activate several
reset outputs
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All the reset signals output of the PRCM are active low
NCHUEE 720A Lab
Prof. Jichiang Tsai
Global Power On Reset (Cold Reset)
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Power On Reset (PORz)
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The source of power on reset is PORz signal on the device
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This reset is non-blockable
PORz can be driven by external power management devices or
power supervisor circuitry
Bad Device Reset
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Everything on device is reset with assertion of power on reset
Asserted whenever an unsupported device type is encoded
Global Cold Software Reset (GLOBAL_COLD_SW_RST)
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Generated internally by the PRM
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Upon setting the RM_RSTCTRL.RST_GLOBAL_COLD_SW bit in
the PRM memory map
NCHUEE 720A Lab
Prof. Jichiang Tsai
Global Warm Reset
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External Warm Reset
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nRESETIN_OUT is a bidirectional warm reset signal
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As an input, it is typically used by an external source as a device reset
As an output, nRESETIN_OUT can be used to reset external devices
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Drive low during a cold reset or an internally generated warm reset
After completion, nRESETIN_OUT will continue to drive low for a period
defined by PRM_RSTTIME.RSTTIME1
RSTTIME1 is a timer that counts down to zero at a rate equal to the high
frequency system input clock CLK_M_OSC
This allows external devices to be held in reset for some time after the
AM335x comes out of reset
The device and its related peripherals are reset together
nRESETIN_OUT also reflects chip reset status
Watchdog Timer and Global Warm Software Reset
NCHUEE 720A Lab
Prof. Jichiang Tsai
Reset Priority
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POR
TRSTz (Trace Functionality Test Reset )
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External warm reset
Emulation
Reset requestors
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Triggered from TRSTz pin on JTAG interface.
A non-blockable reset and resets test and emulation logic
The reset from the watchdog timer is not blockable
Software resets
NCHUEE 720A Lab
Prof. Jichiang Tsai
Power-Up/Down Sequence

Each power domain has dedicated warm and cold reset
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Warm reset gets asserted each time there is any warm reset
source requesting reset
Warm reset is also asserted when power domain moves from
ON to OFF state
Cold reset for the domain is asserted in response to cold reset
sources
When domain moves from OFF to ON state, cold reset also
gets asserted

This is similar to power-up condition for that domain
NCHUEE 720A Lab
Prof. Jichiang Tsai