Specifications

64 158004.B00
-kxxx -k kicks the watchdog timer for <xxx> seconds. The xxx parameter is a
hexadecimal number in the range 0 - 1FFh.
6.9 WATCHDOG TIMER PROGRAMMING
The watchdog timer is contained within the serial EEPROM chip and is controlled
through four pins of the Utility Register. Once it is enabled, the watchdog timer will
reset the TP400 if it is not accessed (or “kicked”) regularly. It is up to the user to write
code to enable and kick the watchdog timer. As an example, the source code of a
watchdog timer test program is included on the TP400 Utility Disks. The test program
is called TP3WDOG.EXE.
The TP3WDOG program has a number of command line options. These can be
reviewed by executing the program with the following command-line:
TP3WDOG –H
Or:
TP3WDOG -?
or just:
TP3WDOG
To start the watchdog timer test type this:
TP3WDOG -T TP400 (you must include the spaces)
The program enables the watchdog timer, and kicks it regularly, until you type S (in
which case the watchdog times out) or anything else, in which case the watchdog
timer is disabled.
The general purpose serial EEPROM program, TP3EE.EXE, can also be used to test
the watchdog timer - see section 6.8.
The watchdog timer is kicked by the toggling of its chip select pin (/CS), which is
driven by the Utility Register bit 4 at I/O address 0E4h. Users might consider taking
the /CS pin low at one point in their program and taking it high again in a different
point. This reduces the likelihood that a crashed program could end up executing a
small loop that both set and cleared the /CS pin. Similarly, the watchdog accesses
should not be part of a timer-based interrupt service routine, since a program could
possibly crash and leave a timer interrupt correctly operating.
Care needs to be taken if the TP400 power management is to be used. Power
management can slow down the processor clock, or even stop it, so that software
loops will execute slowly, or even stop entirely. Thus the possibility exists that
watchdog timer would time out.
Consequently, the BIOS disables the watchdog timer before entering Standby or
Suspend modes, and re-enables it after resuming high speed operation. Users must
be aware of this. In low speed mode the watchdog timer remains operational. Users
must confirm that the slow CPU speed still allows the watchdog to be kicked.