uccjcm@ecsvax.UUCP (John McLendon) (03/24/89)
We have a real-time application that requires tight control loops
to monitor "processes." Okay, so we get on support to get some
reliable answers to some questions concerning the HP-9000/360
HP-UX 6.21 Instrument Controller. First question to support is
"What is the average & maximum interrupt latency on the 360?"
Answer is 10 millisecs & 20 millisecs respectively!
My question to the HP wizards is is this true? That seems a-w-f-u-l-l-y
sloooooooow. What I'm hearing is that interrupts are serviced
whenever a time slice rolls around. Is this true? Think about
what this means.... Only one DMA transfer can happen in one time slice.
All i/o must be hardware buffered. A process that does a plock
& rtprio(0,0) is uninteruptable. In fact, the clock can't even tick.
What I'd like to know is where did
the 68k interrupt levels 3-6 go to. If I write a driver and attach
it to one of these (hardware) interrupts, will I get a chance to
service it before 19.999999 millisecs go by? What is the latency
to this hardware interrupt? In the same vein, once I get control
to service the interrupt, how long can I keep control (mask
other hardware interrupts) w/o causing untoward effects. The
figure I've heard (non-hp source) is about 20 assembly instructions?
Is this true? Any and all comments/help/flames appreciated.
Thanks,
John...
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