Re: wait/dealy inside a record

[Andrew Johnson <anj@aps.anl.gov>]

Hi Stefen,

On 08/12/2016 02:48 AM, Stefen Paul wrote:
> I'm using a waveform record (with custom device support) for writing &
> reading a hardware.
> 
> I need following sequence:
> 
> - write to a register
> - wait for 20 microseconds
> - again write to the same register
> - again wait for 20 microseconds
> - read an array of other registers
> 
> Any tips on how can I generate a delay/wait of ~20 microsec inside the
> device support routine  or otherwise in EPICS ?

40 microseconds is probably a bit too long for your device routine to
block record processing, so Michael's suggestion that you use an
asynchronous completion callback is sensible. That requires you to
implement the write/delay/write/delay/read sequence yourself though,
probably in another thread, and to communicate between threads.

An alternative approach that I recommend looking at is to use
asynDriver's Port Driver C++ class, which can simplify the device
support code quite a bit and allows you to write the above sequence as
what looks like single-threaded code. Your 20µs delays could then become
calls to the OS' nanosleep() routine or an equivalent. The asynDriver
infrastructure will run this code in a separate thread at the
appropriate time and handle the communication with the record for you.

http://www.aps.anl.gov/epics/modules/soft/asyn/R4-29/asynPortDriver.html
http://www.aps.anl.gov/epics/modules/soft/asyn/R4-29/asynDriver.html

HTH,

- Andrew

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