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Power, Reset, and Clock Management
• Interface clock management is done at the device level.
• From the standpoint of the PRCM module, an interface clock is identified by an _ICLK suffix.
Functional clocks have the following characteristics:
• They supply the functional part of a module or subsystem.
• A module can have one or more functional clocks. Some functional clocks are mandatory, while others
are optional. A module needs its mandatory clock(s) to be operational. The optional clocks are used for
specific features and can be shut down without stopping the module activity
• From the standpoint of the PRCM module, a functional clock is distributed directly to the related
modules through a dedicated clock tree. It is identified with an _FCLK suffix
8.1.3.2 Module-Level Clock Management
Each module in the device may also have specific clock requirements. Certain module clocks must be
active when operating in specific modes, or may be gated otherwise. Globally, the activation and gating of
the module clocks are managed by the PRCM module. Hence, 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 for device modules based on whether the module can initiate transactions on the device
interconnect (called master module or initiators) or cannot initiate transactions and only responds to the
transactions initiated by the master (called slave module or targets). Thus, two hardware-based power-
management protocols are used:
• Master standby protocol: Clock-management protocol between the PRCM and master modules.
• Slave idle protocol: Clock-management protocol between the PRCM and slave modules.
8.1.3.2.1 Master Standby Protocol
Master standby protocol is used to indicate that a master module must initiate a transaction on the device
interconnect and requests specific (functional and interface) clocks for the purpose. The PRCM module
ensures that the required clocks are active when the master module requests the PRCM module to enable
them. This is called a module wake-up transition and the module is said to be functional after this
transition completes. Similarly, 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. Although the protocol is completely hardware-controlled, software must configure the
clock-management behavior for the module. This is done by setting the module register bit field
<Module>_SYSCONFIG.MIDLEMODE or <Module>_SYSCONFIG.STANDBYMODE. The behavior,
identified by standby mode values, must be configured.
Table 8-1. Master Module Standby-Mode Settings
Standby Mode Value Selected Mode Description
The module unconditionally asserts the
standby request to the PRCM module,
regardless of its internal operations. The
PRCM module may gate the functional
0x0 Force-standby
and interface clocks to the module. This
mode must be used carefully because it
does not prevent the loss of data at the
time the clocks are gated.
The module never asserts the standby
request to the PRCM module. This mode
is safe from a module point of view
because it ensures that the clocks remain
0x1 No-standby
active. However, it is not efficient from a
power-saving perspective because it
never allows the output clocks of the
PRCM module to be gated
501
SPRUH73H–October 2011–Revised April 2013 Power, Reset, and Clock Management (PRCM)
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