Emergency action during software hang problem

Hi,

We are doing a project for US client and its a somewhat critical project. The system software frequently goes to hang state, so we are decided to to use a Watch Dog Timer (WDT) to reset the someone. Here i need your valuable comments regarding what to do with this WDT either we need to shutdown the hardware or software reset is enough? Because this is a medical device project needs to take a care.

medical devices need to be certified for being used in safety critical aplications.... You need to get the TUV certification... So its obvious you have to follow the standards they have prescribed, and your device has to pass the certification....

What RTOs are you using for the medical device, and what watch dog timer are you depending external or internal..... One thing you can or never shut down the system or your system should be roboust for "fail safe". first what is the circumstance or reason your software hangs? might not be a reliable way of developing the software if you do a detailed study of TUV standards.....

the system should be taken to fail safe state always, or you should use a redundand processor that would or should take over the control if one processor fails....

your design needs more roboust design.. track the reason or bug that is hanging the software and target it first...
make software stable and roboust, then you can think of wdt action or else resetting everytime the system is never a solution..... or shutting down a system which is monitoring a critical parameter of the patient.......

oh....sorry friends, actually software does not hang frequently. According to safety issue consideration, we are try to implement the WDT if software fails in a worst case condition. For that we plan to place a WDT to solve the problem (this is for worst case or safety purpose only). and Our plan is to reset the software if code fails, is it worth-full? or need to change to another solution?

//What RTOs are you using for the medical device, and what watch dog timer are you depending external or internal..... One thing you can or never shut down the system or your system should be roboust for "fail safe". first what is the circumstance or reason your software hangs? //

We are planning to use an internal WDT of DSP IC. Yes, here we planned to shutdown only the emergency solenoid switches not full system. After that do a software reset to bring the system back to normal condition.

there are different steps that can be done....
1. retry mechanism
2. forward and backward recovery mechanism
3. failure assertion techniques
4. memorising the executed state
5. graceful degradation

software reset might not probably bring the system to normal condition always...