The problem with a boot-time watchdog timer… how do you know how long to wait for the system to boot? The idea with modern operating system kernels, and especially with embedded operating systems, is that you want the kernel to boot as quickly as possible, naturally. If you must reconfigure the boot-time watchdog timer in software… this can be done from EEPROM. Parameters:
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Enable/disable
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Timeout (in seconds)
So how do you change the configuration if you cannot boot your operating system? At the very least, last resort, there can be a hardware DIP switch override to disable the boot-time watchdog timer.
UPDATE 2020-10-10: Note that microcontrollers like the AVR can be configured to enable the watchdog timer at boot. So indeed there are commercial products already with the solution to the issue I’ve just described, it’s just that it’s not consistent for more powerful embedded CPUs.