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Table Of Contents

Contents
- Figures
- Tables
- Revision History
Preface
- P.1 About the EP93xx User’s Guide
- P.2 Related Documents from Cirrus Logic
- P.3 Reference Documents
- P.4 Notational Conventions
- P.5 Register Example
Introduction
- 1.1 Introduction
- 1.2 EP93xx Features
- 1.3 EP93xx Processor Applications
- 1.4 EP93xx Processor Highlights
ARM920T Core and Advanced High-Speed Bus (AHB)
- 2.1 Introduction
- 2.2 Overview: ARM920T Core
- 2.3 AHB Decoder
MaverickCrunch Co-Processor
- 3.1 Introduction
- 3.2 Programming Examples
  - 3.2.1 Example 1
  - 3.2.2 Example 2
    - 3.2.2.1 C Code
    - 3.2.2.2 MaverickCrunch Assembly Language Instructions
- 3.3 DSPSC Register
- 3.4 ARM Co-Processor Instruction Format
- 3.5 Instruction Set for the MaverickCrunch Co-Processor
Boot ROM
- 4.1 Introduction
  - 4.1.1 Boot ROM Hardware Operational Overview
    - 4.1.1.1 Memory Map
  - 4.1.2 Boot ROM Software Operational Overview
- 4.2 Boot Options
System Controller
- 5.1 Introduction
- 5.2 Registers
Vectored Interrupt Controller
- 6.1 Introduction
- 6.2 Registers
Raster Engine With Analog/LCD Integrated Timing and Interface
- 7.1 Introduction
- 7.2 Features
- 7.3 Raster Engine Features Overview
- 7.4 Functional Details
- 7.5 Registers
Graphics Accelerator
- 8.1 Overview
- 8.2 Block Processing Modes
- 8.3 Line Draws
  - 8.3.1 Breshenham Line Draws
  - 8.3.2 Pixel Step Line Draws
- 8.4 Memory Organization for Graphics Accelerator
- 8.5 Register Programming
  - 8.5.1 Word Count
    - 8.5.1.1 Example: 8 BPP mode
    - 8.5.1.2 Example: 24 BPP (packed) mode
  - 8.5.2 Pixel End and Start
- 8.6 Register Usage
- 8.7 Registers
1/10/100 Mbps Ethernet LAN Controller
- 9.1 Introduction
- 9.2 Descriptor Processor
- 9.3 Registers
DMA Controller
- 10.1 Introduction
- 10.2 Registers
  - 10.2.1 DMA Controller Memory Map
  - 10.2.2 Internal M2P/P2M Channel Register Map
Universal Serial Bus Host Controller
- 11.1 Introduction
  - 11.1.1 Features
- 11.2 Overview
- 11.3 Registers
Static Memory Controller
- 12.1 Introduction
- 12.2 Static Memory Controller Operation
- 12.3 PCMCIA Interface (EP9315 Processor Only)
- 12.4 PC Card Memory-Mode Enable Signals
- 12.5 PC Card Memory Mapping
- 12.6 Registers
  - 12.6.1 Bank Configuration Registers
  - 12.6.2 PCMCIA Configuration Registers (EP9315 Processor Only)
SDRAM, SyncROM, and SyncFLASH Controller
- 13.1 Introduction
- 13.2 Booting from SyncROM or SyncFLASH
- 13.3 Address Pin Usage
- 13.4 SDRAM Initialization
- 13.5 Programming Mode Register: SDRAM Or SyncROM Device
- 13.6 SDRAM Self Refresh
  - 13.6.1 Entering Self Refresh Mode
  - 13.6.2 Exiting Self Refresh Mode
- 13.7 Programming Registers: SyncFLASH Device
- 13.8 External Synchronous Memory System
  - 13.8.1 Chip Select SDCSN[3:0] Decoding
  - 13.8.2 Address/Data/Control Required by Memory System
- 13.9 Registers
UART1 With HDLC and Modem Control Signals
- 14.1 Introduction
- 14.2 UART Overview
- 14.3 Modem
- 14.4 HDLC
- 14.5 UART1 Package Dependency
  - 14.5.1 Clocking Requirements
  - 14.5.2 Bus Bandwidth Requirements
- 14.1 Registers
UART2
- 15.1 Introduction
- 15.2 IrDA SIR Block
- 15.3 UART2 Package Dependency
  - 15.3.1 Clocking Requirements
  - 15.3.2 Bus Bandwidth Requirements
- 15.4 Registers
UART3 With HDLC Encoder
- 16.1 Introduction
- 16.2 Implementation Details
- 16.3 Registers
IrDA
- 17.1 Introduction
- 17.2 IrDA Interfaces
- 17.3 Shared IrDA Interface Feature
- 17.4 Medium IrDA Specific Features
  - 17.4.1 Introduction
    - 17.4.1.1 Bit Encoding
    - 17.4.1.2 Frame Format
  - 17.4.2 Functional Description
- 17.5 Fast IrDA Specific Features
- 17.6 Registers
Timers
- 18.1 Introduction
- 18.2 Registers
Watchdog Timer
- 19.1 Introduction
- 19.1 Registers
Real Time Clock With Software Trim
- 20.1 Introduction
  - 20.1.1 Software Trim
  - 20.1.2 Reset Control
- 20.1 Registers
I2S Controller
- 21.1 Introduction
- 21.2 I2S Transmitter Channel Overview
- 21.3 I2S Receiver Channel Overview
  - 21.3.1 Receiver FIFO’s
- 21.4 I2S Master Clock Generation
- 21.5 I2S Bit Clock Rate Generation
  - 21.5.1 Example of the Bit Clock Generation.
  - 21.5.2 Example of Right Justified LRCK format
- 21.6 Interrupts
- 21.7 Registers
AC’97 Controller
- 22.1 Introduction
- 22.2 Interrupts
  - 22.2.1 Channel Interrupts
  - 22.2.2 Global Interrupts
- 22.3 System Loopback Testing
- 22.4 Registers
Synchronous Serial Port
- 23.1 Introduction
- 23.2 Features
- 23.3 SSP Functionality
- 23.4 SSP Pin Multiplex
- 23.5 Configuring the SSP
- 23.6 Registers
Pulse Width Modulator
- 24.1 Introduction
- 24.2 Theory of Operation
  - 24.2.1 PWM Programming Examples
  - 24.2.2 Programming Rules
- 24.3 Registers
Analog Touch Screen Interface
- 25.1 Introduction
- 25.2 Touch Screen Controller Operation
- 25.3 Registers
Keypad Interface
- 26.1 Introduction
- 26.2 Theory of Operation
- 26.3 Registers
IDE Interface
- 27.1 Introduction
- 27.2 Theory of Operation
- 27.3 Registers
GPIO Interface
- 28.1 Introduction
- 28.2 Registers
Security
- 29.1 Introduction
- 29.2 Features
- 29.3 Contact Information
- 29.4 Registers
Glossary
EP93XX Register List

DS785UM1 19-1

Chapter 19

19Watchdog Timer

19.1 Introduction

The Watchdog Timer provides a mechanism for generating a system-wide reset should the

system hang. This functionality allows the Watchdog to recover the system and report the

recovery to software. To prevent system-wide reset, software must periodically reset the

Watchdog via an APB write operation. It is possible to disable the Watchdog through either

hardware or software.

The Watchdog timer circuitry consists of a 7-bit counter. The most significant bit of the

counter is used to trigger the WATCHDOG_RESETn output signal to the system control

module for generating HRESETn.

The amount of time before a WATCHDOG_RESETn is initiated as well as the duration of the

reset pulse is as follows:

• Time-out or WATCHDOG_RESETn duration = 64 / WATCHDOG_CLK frequency (units

are seconds).

• For a 256 Hz WATCHDOG_CLK, time-out and reset pulse duration are

64 / 256 = 250 msec.

To keep the reset pulse from occurring, SW must reset the Watchdog timer (sometimes

known as “kick the dog”) to a predetermined count on a periodic basis. This resets the

counter, which prevents the WATCH_RESETn from activating. The counter is reset by writing

0x5555 to the Watchdog register. The Watchdog should be reset at least 2

WATCHDOG_CLK periods earlier than the time-out calculation would indicate, due to clock

synchronization and handshaking circuitry.

Once a Watchdog reset occurs, the timer also provides a 250 ms duration reset pulse. The

Watchdog also defaults to providing the pulse duration when the reset is from other sources

such as user reset (external reset on RSTOn), AMBA bus reset (HRESETn), or power on

reset (internal chip voltage detect power on signal PWR_RESETn). The reset pulse duration

can be disabled by pulling the CSn[2] (HW_RSTPULSE_DISABLEn) signal low during the

bus reset (HRESETn low). This immediately frees the Watchdog reset output line when reset

becomes inactive. In either case, if the reset pulse duration is provided or not, the Watchdog

counter will start over after the WATCHDOG_RESETn output becomes inactive. This begins

a new 250 ms cycle after reset becomes inactive before software must reset the counter.