What happens when server crash - Raspberry Pi Forums

i want make alarm can control true webpage. webpage been worked on 's not realy problem.
gpio have been checked when alarm on. happens when server crasht ? i'm thinking 3 solutions not know need choose security. because system needs work !

- using php on webserver , controlling gpio on way
- using c++ program data webpage , control gpio ( not know if still works when server crash ?
because rpi still performance or happens ? )
- using external hardware i2c connection , use rpi webpage , controlling i/o happen without rpi.

english not

hi,

gilles951 wrote:i want make alarm

went trough message couple of times issue, let me see if understand:
- raspi monitoring (external alarm system) gpio pin
- raspi running web server you'd monitor alarm system thing,
- have concerns raspi crashes, need automatically restore state working one.

correct ?

approach add small circuit (hardware), isolated as possible monitored raspi.
let's call hardware watchdog.

setup:
- watchdog has input connected raspi's gpio pin.
- watchdog has output connected raspi's reset header (first raspi versions don't have it).
operation:
- raspi needs toggle watchdog-monitored gpio pin in regular intervals
- if pin not triggered within amount of time (eg. 3 minutes), watchdog resets raspi.
details:
- watchdog timeout interval needs long enough enable raspi boot , start programs
- important watchdog requires gpio's pin transitions low-to-high , high-to-low (not level of pin, prevent undetected crash).

circuit done discrete components (logic gates, few capacitors, etc.) or build around small microcontroller.
i'd assume these circuits have been described in details on web pages (ask google).


best wishes, ivan zilic.

raspberrypi