Re: Use of asyn's setInterruptUInt32Digital in EPICS device support

[Mark Rivers via Tech-talk <tech-talk at aps.anl.gov>]

Hi Jure,

> I’m looking at `asynPortDriver::setInterruptUInt32Digital()' which is documented to be “called when asyn clients call `pasynUInt32Digital->setInterrupt()'”.
> However, EPICS device support (`devAsynUInt32Digital.c') does not contain such a call.

You are looking in the wrong place for that call.  That call is not part of device support, it is part of the asynUInt32Digital interface, and so is present here:

https://github.com/epics-modules/asyn/blob/a2f59505766f5a19af1afb325fc84b3a1d77552f/asyn/interfaces/asynUInt32Digital.h#L44

pasynUInt32Digital->setInterrupt() is used to configure the driver to control which bits will generate interrupts.  

It is implemented in the IPUnidig driver, for example:

https://github.com/epics-modules/ipUnidig/blob/990c5920e6a50f17b164db0477ccfdc28df97442/ipUnidigApp/src/drvIpUnidig.cpp#L543

> I’d expect, from the driver point of view, to be able to use `asynPortDriver::getInterruptUInt32Digital()' to learn which bits records are interested in. 

No, it is the reverse.  Device support calls getInterruptUInt32Digital() to learn which bits the hardware has configured to generate interrupts.

> • On read or write, `asynUInt32Digital' passes the mask and the value to/from in the way appropriate for the device.

Yes, that is true.

>  For interrupts, `asynPortDriver' will consider the mask given to `setUIntDigitalParam()' and figure out which `IO Intr' records to process based on both the mask and which bits in the value have changed.

Yes, that is true.  But this has nothing to do with driver/hardware interrupts, which is what setInterruptUInt32Digital() is designed to control.

> If the last point is true, then I guess `asynPortDriver::setInterruptUInt32Digital()' really doesn’t seem useful for EPICS. I hope now you see why I’m wondering what it’s about

You are mixing up software interrupts which are handled using callbacks for records with SCAN=I/O Intr with driver/hardware interrupts.  They are completely separate.  asynPortDriver::setInterruptUInt32Digital() only controls driver/hardware interrupts, which is why it is not used in many places.

Mark

From: Tech-talk <tech-talk-bounces at aps.anl.gov> on behalf of Jure Varlec via Tech-talk <tech-talk at aps.anl.gov>
Sent: Wednesday, January 26, 2022 2:32 AM
To: tech-talk at aps.anl.gov <tech-talk at aps.anl.gov>
Subject: Use of asyn's setInterruptUInt32Digital in EPICS device support

 

Dear all,

I’m looking at `asynPortDriver::setInterruptUInt32Digital()' which is documented
to be “called when asyn clients call `pasynUInt32Digital->setInterrupt()'”.
However, EPICS device support (`devAsynUInt32Digital.c') does not contain such a
call.

It’s not clear to me how this interface is meant to be used. I’d expect, from
the driver point of view, to be able to use
`asynPortDriver::getInterruptUInt32Digital()' to learn which bits records are
interested in. However, this does not work with EPICS, I don’t see how it could
be set to logical-or of masks for all `IO Intr' records, and I don’t see a use
case for anything else. I don’t have a use case myself; I’m just wondering how
the interface works and what it is meant for, presuming that it was implemented
with some purpose in mind.

Actually, I feel a bit unsure as to how the mask in the UInt32Digital interface
really works. The documentation appears to be quite sparse on this topic. My
understanding is the following:

• `asynInt32' deals with the mask in EPICS device support layer support while
  `asynUInt32Digital' delegates that to the driver.
• On read or write, `asynUInt32Digital' passes the mask and the value to/from
  the driver unmodified. It’s up to the driver to apply the mask to the value
  in the way appropriate for the device.
• For interrupts, `asynPortDriver' will consider the mask given to
  `setUIntDigitalParam()' and figure out which `IO Intr' records to process
  based on both the mask and which bits in the value have changed.

If the last point is true, then I guess
`asynPortDriver::setInterruptUInt32Digital()' really doesn’t seem useful for
EPICS. I hope now you see why I’m wondering what it’s about :)

Best regards,

Jure Varlec
Senior Software Developer
Cosylab d.d.
www.cosylab.com