Intel® Arria® 10 Hard Processor System Technical Reference Manual

ID 683711
Date 8/28/2023
Public
Document Table of Contents

25.4.7. Watchdog Timer State Machine

The following figure illustrates the behavior of the watchdog timer, including the behavior of both output response modes. Once initialized, the counter decrements at every clock cycle. The state machine remains in the Decrement Counter state until the counter reaches zero, or the watchdog timer is restarted. If software reads the interrupt clear register (wdt_eoi), or writes 0x76 to the wdt_crr register, the state changes from Decrement Counter to Load Counter with Restart Timeout Value. In this state, the watchdog counter gets reloaded with the restart timeout value, and then the state changes back to Decrement Counter.
Figure 152. Watchdog Timer State Machine

If the counter reaches zero, the state changes based on the value of the output response mode setting defined in the rmod bit of the wdt_cr register. If the rmod bit of the wdt_cr register is 0, the output response mode is to generate a system reset request. In this case, the state changes to Assert System Reset Request. In response, the reset manager resets and disables the watchdog timer, and gives software the opportunity to reinitialize the timer.

If the rmod bit of the wdt_cr register is 1, the output response mode is to generate an interrupt. In this case, the state changes to Assert Interrupt and Load Counter with Restart Timeout Value. An interrupt to the processor is generated, and the watchdog counter is reloaded with the restart timeout value. The state then changes to the second Decrement Counter state, and the counter resumes decrementing. If software reads the wdt_eoi register, or writes 0x76 to the wdt_crr register, the state changes from Decrement Counter to Load Counter with Restart Timeout Value. In this state, the watchdog counter gets reloaded with the restart timeout value, and then the state changes back to the first Decrement Counter state. If the counter again reaches zero, the state changes to Assert System Reset Request. In response, the reset manager resets the watchdog timer, and gives software the opportunity to reinitialize the timer.