From: muratlanne@gmail.com   
      
   "Morris Dovey"  wrote in message   
   news:jg6chm$98j$1@speranza.aioe.org...   
   > On 1/30/12 7:26 AM, Jim Wilkins wrote:   
   >> ...   
   > (2) schd() accepts a date/time number and a pointer to the code that I   
   > want to run at that time, and stores these away in a linked list that's   
   > ordered so that the soonest-to-run request is always at the top of the   
   > list.   
   >   
   > (3) dispatch() compares the current time to the requested run time for the   
   > top/first element on the list. If it's ripe, the element is moved from the   
   > 'pending' list to the 'idle' list for recycling, and the code at the   
   > pointer is called....   
   > >   
   > My Arduino setup() routine does the usual pin assignments, etc. and then   
   > makes a call to the reactor monitoring routine, which captures and logs   
   > data, schedules itself to run again in 1000 milliseconds, and returns. If   
   > it finds a condition that needs action, it calls other code (which may   
   > start other threads, ad nausea)....   
   >   
   > The busiest this thing will ever be is during an emergency shutdown, when   
   > all of the motors, valves, etc. will be operating   
   > concurrently/asynchronously - and not even all that will result in   
   > noticable CPU loading....   
   > Morris Dovey   
      
   It sounds to me like you would detect an error condition by polling rather   
   than interrupts from switches, and then schedule a service routine. If mild   
   and major faults occur simultaneously, like overtemp and pressure, would it   
   service both alternately or only the one tested last and thus scheduled   
   soonest?   
      
   I ask because the standard cell IC I designed was a dynamic memory   
   controller for a flat-bed color scanner that prioritized asynchronous memory   
   access requests from the CCD array, CPU, GPIB output and refresh controller,   
   in that order. It absolutely had to accept CCD input before the next word   
   arrived, but couldn't allow the lower priority requests to pile up too long.   
   That startup company folded before I had a chance to test the completed   
   machine and see how well my chip worked.   
      
   As a hardware guy I always expect a sensor failure or wiring problem. On one   
   safety-critical machine the sensor switches were biased by resistor networks   
   and sensed by the A/D converter, so the windows were say zero to 1V = sensor   
   or wiring shorted, 1V to 2V = valid low, 2V to 3V = fault???, 3V to 4V =   
   valid high, >4V = sensor or wire open. Thermocouples were biased to indicate   
   the lowest negative temperature if open. The A/D converter itself was a   
   single-point failure node, but was easily tested by checking supply and   
   reference voltages, and there were two processors and sets of redundant   
   switches. In addition it had a dead-man shutdown that killed power, leaving   
   everything in a power-off condition chosen to be the safest, such as landing   
   gear down. That's why I asked you about solenoid valves. I'd have   
   normally-closed on the hydrogen input and normally-open on the dump line.   
      
   jsw   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)