Watchdog Timer
UG0331 User Guide Revision 15.0
631
The memory map address for the watchdog timer is 0x40005000-0x40005FFF. The 32-bit counter in the
watchdog timer is clocked with the clock signal from the RC Oscillator (RCOSCCLK) which has a
frequency of 50 MHz (if Vdd = 1.2 V) with a 5% tolerance.
20.2.1.3 Timeout Detection
A control bit in the WDOGCONTROL register is used to determine whether the watchdog timer
generates a reset or an interrupt if a counter timeout occurs. The default setting is reset generation on
timeout. When interrupt generation is selected, the WDOGTIMEOUTINT output is asserted on timeout
and remains asserted until the interrupt is cleared. When reset generation is selected, the watchdog
timer does not directly generate the system reset signal. Instead, when the counter reaches zero, the
watchdog timer generates a pulse on the WDOGTIMEOUT output and this is routed to the reset
controller to cause it to assert the necessary reset signals. The pulse on the WDOGTIMEOUT output is
generated in the RCOSCCLK domain and has duration of one clock cycle.
20.2.2
Port List
The following table lists the ports of the Watchdog Timer module.
20.2.3
Details of Operation
This section provides the details of operation of Watchdog timer.
20.2.3.1 Loading and Refreshing the Watchdog Timer
The WDOGLOAD register is used to store the value that is loaded into the counter each time the
watchdog timer is refreshed. The six least significant bits of the WDOGLOAD register are always set to
0x3F, irrespective of what value is written to it. This effectively means that there is a lower limit on the
value that can be written to the counter. After refreshing, at least 64 RCOSCCLK clock ticks (0.00128ms
for Vdd=1.2 V) are required before the counter times out. The purpose of this feature is to prevent a
watchdog timer reset/interrupt from occurring immediately after, or during refresh in the case where a
very low value has been written to the WDOGLOAD register.
The watchdog timer counter is refreshed by writing the value 0xAC15DE42 to the WDOGREFRESH
register. This causes the counter to be loaded with the value in the WDOGLOAD register as defined in
the system register block shown in
An appropriate value must be written to the WDOGLOAD System register before writing to the
WDOGREFRESH register. Forbidden and permitted windows in time regulate when refreshing can
occur. The size of these windows is controlled by the value in the WDOGMVRP System register.
When the counter value is greater than the value in the WDOGMVRP, refreshing the watchdog timer is
forbidden. If a refresh is executed in these circumstances, the refresh is successful, but a reset or
interrupt (depending on Operation mode selected) is also generated. This is shown in the following
figure.
When the counter value falls below the level programmed in the WDOGMVRP, refreshing of the
watchdog timer is permitted. It is possible to avoid having forbidden and permitted windows by ensuring
that the value in the WDOGMVRP is greater than the value in the WDOGLOAD.
Table 633 •
Watchdog Timer Interface Signals
Name
Type
Width
Description
WDOGTIMEOUTINT
Output 1
This interrupt is asserted, if the counter reaches zero and interrupt rather
than reset generation has been selected on counter timeout.
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