Cirrus Logic EP93xx - Manual (Page 127)

DS785UM1 5-1
Copyright 2007 Cirrus Logic
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5
5
Chapter 5
5 System Controller
5.1 Introduction
The System Controller (Syscon) provides:
• Clock control
• Power management
• System configuration management
These central resources are controlled by a set of software-locked registers, which can be
used to prevent accidental accesses. Syscon generates the various bus and peripheral
clocks and controls the system startup configuration.
5.1.1 System Startup
System startup begins with the assertion of a reset signal. There are five different categories
of reset events. In order of decreasing effect, the reset events are:
• PRSTn (external pin for power-on reset)
• RSTOn (external pin for user reset)
• Three-key reset externally generated by a Keypad (behaves like user reset)
• Watchdog reset (internally generated)
• Software reset (internally generated)
During the time that any reset is active, the system is halted until it exits the reset state.
When the device starts with an external PRSTn or RSTOn, certain hardware configurations
are determined, and some system configuration information will be recorded so that software
can access it. See the details in
“System Reset” on page 5-1 and “Hardware Configuration
Control” on page 5-2 .
5.1.2 System Reset
The device system reset consists of several events and signals. It has four levels of reset
control:
• Power-on-reset, controlled by PRSTn pin. It resets the entire processor with no
exceptions.
• User reset, controlled by RSTOn pin. While active, it resets the entire processor, except