![]() ![]() I've just taken the blind faith that these technologies are secure and uncrackable. So, I really need to study security more. Time-based rolling token - why is it secure? Security.For instance, a friend from a past job had this bizarr. In a recent Snap! there was an article about "Super-recognizers" who can remember any face, and how they can actually help fight crime in real life.I've met people who seem to have other superpowers. What are your favorite real-life superpowers? Spiceworks.You can spend your Friday racking up high scores. Anyway, I have included a couple of links so ![]() Spent hours playing this game both at the Arcade and on my Atari 2600. Spark! Pro series – 22nd May 2023 Spiceworks Originals.I have a client who has leased some public IP's from different subnets,įor demonstration purposes, lets say these are "82.99.15.65/27" and Hi everyone! I'm stuck on a tough case and i could really need your Ubiquiti expertise. Dream Machine Pro - Routing public IP's Networking.If a watchdog were to fail along with the MCU (perhaps the entire PCB burns out), mechanical hardware fail safes might be the next step for ensuring safety. WDTs are not necessarily the last line of defense, however. Regardless, the watchdog timer has been around for decades and is still a reliable method to maintain an electronic fail-safe. (Maybe “time bomb” would have been a more accurate description, but it wouldn’t sound quite right to talk about bombs in your system, either.) The act of resetting the WDT has been referred to as “kicking the dog.” According to Niall Murphy (by way of Jack Ganssle), “If the man stops kicking the dog, the dog will take advantage of the hesitation and bite the man.” If you take too long to kick the dog, the dog bites you by resetting the MCU. “Watchdog” may seem a curious choice of words, but there’s a metaphor in there. Once the MCU has gone off the rails, software checks are likely to be ignored, bypassed, overwritten, or just plain forgotten as a rogue event can wreak exquisite havoc. It’s possible that a single cosmic ray can obliterate a single register in flash memory that causes a stack overflow and infinite loops. MCUs don’t necessarily lose their mind that often, at least they aren’t supposed to, but in critical systems, you cannot trust that something won’t happen. You can’t expect something at risk of possibly losing its mind to mind its own safety. What if the cruise control program gets stuck in the acceleration mode? The MCU running the cruise control program may need a watchdog timer, which is a kind of external check. Smartphones can be rebooted with a power-cycle off and on (usually when you need to make an urgent call), but how do you power down the MCU that runs the cruise control in your car? Turning off the car would definitely reboot the cruise control loop, but this option is obviously not safe at a high rate of speed. The first WDT, if not reset, may trigger consequences akin to a soft-boot rather than a hard boot. A bit unusual for embedded WDTs, this nested WDT gives the system up to 3 chances to reset the WDT before resetting the computer. Figure 1: This computer WDT has 3 stages of successive WDTs. A watchdog can be an external component in a separate package from the integrated circuit (IC) that houses the MCU (best), or a watchdog can be found inside the IC but on a different circuit from the MCU, however a WDT that’s dependent on the same resources as the MCU might not be a good idea for obvious reasons. It’s best to keep a watchdog external and unreachable by MCU code. But as long as the MCU is running, it will continue to ping the watchdog to reset the timer. Like a bomb, the watchdog timer is set to count down and if it times out, it resets the MCU, dumping programs and rebooting the MCU and probably other areas in the system that work in tandem with the MCU. The MCU checks in with the watchdog timer at a set interval to show that it’s still on the job. Watchdog timers (WDTs), or watchdogs, are circuits external to the processor that can detect and trigger a processor reset (and/or another event) if necessary. (The BSoD happens much less often these days.) Embedded systems are different from desktop computers, however, in that there is rarely going to be a human around who will know how to reboot the failing device. In “the old days,” the Windows operating system would occasionally crash (experience a fatal error) and put up what was called the Blue Screen of Death (BSoD) where after it would reboot to prevent damage to the computer such as writing over vital boot code or similarly dangerous events. If a program goes haywire or into an infinite loop, it needs a way to check and see if things are still running. In the world of microcontrollers (MCUs), sometimes things go wrong. ![]()
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