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Subscribe to Seeking advice: Time-sensitive operations when writing Bug App in JVM  4 posts, 4 voices , Tagged: jvm rtos realtime serial java app vonhippel questions

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Apr 9, 2010 12:57pm
Medium wwward 8 posts

Backstory:  I am looking to implement an existing serial protocol decoder using the VonHippel and the Bug.  Ideally, we could accomplish this with a minimum of additional hardware, so bit-banging the pins on the VonHippel (with appropriate passive components hanging from that) would be more desirable than attaching an external microcontroller.  This also opens up the possibility for advanced software signal processing to identify issues with the serial line, perhaps using the ADC to sample the signal and provide user feedback on observed behavior if there is a fault.  An external dedicated MCU would be more difficult to code that sort of exception logic into.

Question:  When tinkering with the VonHippel module using a “blink the LED” sample app, I noticed the timing on the blinking cycles was a little variable, probably due to other processes delaying the execution of the JVM threads.  I’m aware that we’re not dealing with a real-time implementation in the JVM, but I am curious what techniques I could employ to get things to occur “fast enough” to do the work.  The serial line has a peak speed of 79 kbit/sec.  At that speed, you have about 13 microseconds per bit.  Clearly you’ll want to have windows of time long enough to encapsulate a full packet read, which is around 4,000 microseconds long according to the spec.

I have not yet looked to determine if this is feasible with the module hardware or not, but my question isn’t so much about the hardware as the programming practice – how do you write time-sensitive routines within the existing Bug JVM implementation, and if that is not feasible, how do you write them within the existing Bug software stack (native binaries,) and is there a means to offload these operations to another aspect of the Bug where execution time is more reliable?

Thanks for the advice, and the time.




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