time
CPU
DWD
Down
Counter
access
to DWD
0
0x1FFFFFF
Preload Register
Value left shifted
set DWD
Preload
enable
DWD
Reset/NMI
11bits
Config
DWD
Window
25%
Write
WD
Keys
Preload Register Value
left shifted 13bits
DWD can NOT be
in this period
served
Open
Window
open window
open window
open window
op.
win
open
window
open
window
open
window
open
window
open window
open window
open window
DWD Down
Counter
50% window
open
window
open
window
25% window
12.5% window
6.25% window
op.
win
op.
win
o
w
3.125% window
o
w
o
w
100% window
Module Operation
440
SPNU503C – March 2018
Copyright © 2018, Texas Instruments Incorporated
Real-Time Interrupt (RTI) Module
service the watchdog by writing the correct sequence in the watchdog key register. This service will cause
the watchdog counter to get reloaded from the preload value and start counting down. If the NMI handler
does not service the watchdog in time, it could count down all the way to zero and wrap around. If the NMI
Handler does not service the watchdog in time, the NMI gets generated continuously, each time the
counter counts to '0'.
The DWWD uses the Digital Watchdog (DWD) preload register (RTIDWDPRLD) setting to define the end-
time of the window. The start-time of the window is defined by a window size configuration
register(RTIWWDSIZECTRL).
The default window size is set to 100%, which corresponds to the DWD functionality of a time-out-only
watchdog. The window size can be selected (through register RTIWWDSIZECTRL) from among 100%,
50%, 25%, 12.5%, 6.25% and 3.125% as shown in
. The window with the respective size will
be opened before the end of the DWD expiration. The user has to serve the watchdog in the window.
Otherwise, a reset or NMI will generate.
shows an DWWD operation example (25% window).
•
Configuration of DWWD
The DWWD preload value (same as DWD preload) can only be configured when the DWWD counter is
disabled. The window size and watchdog reaction to a violation can be configured even after the
watchdog has been enabled. Any changes to the window size and watchdog reaction configurations will
only take effect after the next servicing of the DWWD. This feature can be utilized to dynamically set
windows of different sizes based on task execution time, adding a program sequence element to the
diagnostic which can improve fault coverage.
Figure 13-10. Digital Windowed Watchdog Timing Example
Figure 13-11. Digital Windowed Watchdog Operation Example (25% Window)