Symphony DSP56724/DSP56725 Multi-Core Audio Processors Reference Manual, Rev. 0
Freescale Semiconductor
12-1
Chapter 12
Watchdog Timer (WDT, WDT_1)
12.1
Introduction
shows the watchdog timer block diagram.
The DSP56724/DSP56725 has two WDT modules: WDT, WDT_1. The only differences between the
WDT and WDT_1 modules is that WDT is used by DSP Core-0 and WDT_1 is used by DSP Core-1. Only
the WDT is described in detail in this chapter.
12.2
WDT Pin-Outs for Different Device Packages
The watchdog timer has a dedicated output pin (WDT). WDT is held high during watchdog timer operation
until the watchdog timer times out. When the watchdog timer times out, the WDT pin is asserted low after
two EXTAL system clock cycle delays. Following a reset of the device, the WDT pin will de-assert high
after two EXTAL system clock cycle delays.
In the DSP56725 (80-pin and 144-pin packages) and the DSP56724 (144-pin package), the WDT and
WDT_1 pins are ‘ORed’ together, so that when either watchdog timer times out, the external pin is
asserted.
The watchdog timer is driven by the DSP’s main system clock (Fsys). Fsys is scaled by a fixed prescaler
(divide by 4096) prior to driving the 16-bit counter. The time-out period can be selected by writing to the
watchdog modulus register (WMR).
Time-out period = 4096
×
(WMR + 1) clocks
•
Example 1: For Fsys = 200 MHz,
Time-out period = 4096
×
($1) = 268,435,456 clocks
Countdown time = (268,435,456 clocks/200,000,000 clocks per second)
Countdown time = 1.3422 seconds
•
Example 2: For Fsys = 150 MHz,
Time-out period = 4096
×
($1) = 268,435,456 clocks
Countdown time = (268,435,456 clocks/150,000,000 clocks per second)
Countdown time = 1.7896 seconds
•
Example 3: For Fsys = 100 MHz,
Time-out period = 4096
×
($ 1) = 25,141 clocks
Countdown time = (25,141 clocks/100,000,000 clocks per second)
Countdown time = 251.41 microseconds