Watchdog timer for computer system reset

A method of resetting a nonfunctioning computer system, comprising the steps of:

• receiving a start signal from a central processing unit (CPU) within said computer system into a watchdog timer, said start signal indicating that said CPU is beginning execution of a particular task;
• measuring a preselected period of time with said watchdog timer upon receiving said start signal;
• generating a timeout signal with said watchdog timer upon expiration of said preselected period of time;
• receiving said timeout signal into a reset circuit coupled to said CPU;
• responsive to said timeout signal, transmitting a nonmaskable interrupt signal to said CPU;
• determining, upon receipt of the nonmaskable interrupt signal, whether said CPU is nonfunctioning;
• and
• after a delay period, providing, with said reset circuit, a hardware reset signal to said CPU in response to said timeout signal to thereby reset said CPU only when said CPU has not responded to the nonmaskable interrupt signal.

A circuit for resetting a nonfunctioning computer system, comprising:

• a central processing unit (CPU) for transmitting task identification data concerning a particular task said CPU is about to execute to a storage location within said computer system, said CPU further for transmitting a start signal indicating that said CPU is beginning execution of said particular task;
• a watchdog timer for receiving said start signal and measuring a preselected period of time in response thereto, said watchdog timer further for generating a timeout signal upon expiration of said preselected period of time, said timeout signal indicating that said particular task has not been executed successfully;
• a reset signal generating circuit for receiving said timeout signal and, in response thereto, transmitting a nonmaskable interrupt signal to said CPU and providing a reset signal to a reset circuit within said CPU, said reset signal generating circuit also for transmitting timeout data to said storage location, said timeout data indicating that expiration of said period of time caused said reset of said CPU;
• and
• a reset circuit within said CPU for receiving said reset signal from the reset signal generating circuit, delaying for a period of time to allow said CPU, responsive to the receipt of the nonmaskable interrupt signal, to avoid a hardware reset when said CPU is functioning properly, and causing a hardware reset of said CPU when said CPU is nonfunctioning.

A method of resetting a nonfunctioning computer system,

• comprising:
• transmitting task identification data to a storage location within said computer system, the task identification data concerning a particular task a central processing unit (CPU) is about to execute;
• transmitting a start signal indicating that said CPU is beginning execution of said particular task from said CPU to a watchdog timer;
• receiving said start signal into said watchdog timer;
• measuring a preselected period of time in response to receipt of said start signal;
• generating a timeout signal with said watchdog timer upon expiration of said preselected period of time, said timeout signal indicating that said particular task has not been executed successfully;
• receiving said timeout signal into a reset signal generating circuit, said reset signal generating circuit providing, in response thereto, a reset signal to a reset circuit within said CPU;
• receiving the reset signal at the reset circuit within said CPU and attempting to vector said CPU to an error handling routine using a nonmaskable interrupt input;
• initiating a hardware reset of said CPU after a delay period when said CPU does not vector to the error handling routine;
• and
• transmitting timeout data from said reset signal generating circuit to said storage location, said timeout data indicating that expiration of said period of time caused said reset of said CPU.

A personal computer, comprising:

• a microprocessor for transmitting identification data concerning a diagnostic routine to be executed to a storage location within said computer, and for transmitting a start signal indicating that said microprocessor is beginning execution of said diagnostic routine;
• a real time clock, coupled to said microprocessor for receiving said start signal, said real time clock beginning to measure a preselected period of time sufficient to allow said microprocessor to execute said diagnostic routine, said real time clock also for generating a timeout signal upon expiration of said preselected period of time, said timeout signal indicating that said particular diagnostic routine has not been executed successfully;
• and
• hardware reset circuitry coupled to said microprocessor for receiving said timeout signal and, in response thereto, providing a nonmaskable interrupt signal to said microprocessor and, after a delay period, a reset signal to said microprocessor to initiate a hardware reset of said personal computer, said microprocessor avoiding a hardware reset of said personal computer only when said personal computer is functioning properly and allowing a reset of said personal computer when said personal computer system is nonfunctioning, said hardware reset circuitry also for transmitting timeout data to said storage location, said timeout data indicating that expiration of said preselected period of time caused said hardware reset of said personal computer.

A method of diagnosing a personal computer, comprising the steps of:

• transmitting identification data to a storage location within said computer, the identification data concerning a diagnostic routine that a microprocessor within said computer is about to execute;
• transmitting a start signal indicating that said microprocessor is beginning execution of said diagnostic routine from said microprocessor to a real time clock;
• receiving said start signal into said real time clock;
• measuring a preselected period of time in response to receipt of said start signal with said real time clock;
• generating a timeout signal with said real time clock upon expiration of said preselected period of time, generation of said timeout signal indicating that said diagnostic routine has not been executed successfully;
• transmitting a nonmaskable interrupt signal to said microprocessor responsive to said timeout signal;
• after a delay period, transmitting a hardware reset signal from said hardware reset circuitry to said microprocessor;
• receiving the hardware reset signal in said microprocessor;
• resetting said personal computer when said personal computer is nonfunctioning;
• and
• transmitting timeout data from said hardware reset circuitry to said storage location, said timeout data indicating that expiration of said period of time caused said reset of said microprocessor.