Watchdog Timer
Watchdog Timer
Watchdog Timer
Watchdog Timer
Resets the C28x if the CPU crashes
Resets the C28x if the CPU crashes
Watchdog counter runs independent of CPU
Watchdog counter runs independent of CPU
If counter overflows, reset or interrupt is
If counter overflows, reset or interrupt is
triggered
triggered
CPU must write correct data key sequence to
CPU must write correct data key sequence to
reset the counter before overflow
reset the counter before overflow
Watchdog must be serviced (or disabled)
Watchdog must be serviced (or disabled)
within ~4.37
within ~4.37
m
m
s after reset (30 MHz
s after reset (30 MHz
OSCCLK for 150 MHz device)
OSCCLK for 150 MHz device)
This translates into 131,072 instructions!
This translates into 131,072 instructions!
The watchdog timer provides a safeguard against CPU crashes by automatically initiating a reset
if it is not serviced by the CPU at regular intervals. In motor control applications, this helps
protect the motor and drive electronics when control is lost due to a CPU lockup. Any CPU reset
will revert the PWM outputs to a high-impedance state, which should turn off the power
converters in a properly designed system.
The watchdog timer is running immediately after system power-up/reset, and must be dealt with
by software soon after. Specifically, you have 4.37 ms (for a 150 MHz device) after any reset
before a watchdog initiated reset will occur. This translates into 131,072 instruction cycles,
which is a seemingly tremendous amount! Indeed, this is plenty of time to get the watchdog
configured as desired and serviced. A failure of your software to properly handle the watchdog
after reset could cause an endless cycle of watchdog initiated resets to occur.
C28x - System Initialization 5 - 5
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