Experimental Physics and
Industrial Control System

Ralph Lange <[email protected]> · Mon, 26 Jul 2010 09:40:36 -0400

 Hi Angus,
On 25.07.2010 20:32, Angus Gratton wrote:

[...]
I'm thinking that each record's OUT link can specify what jumper
settings are applied on the channel, ie OUT, "#C2 S3 @5v BIP" says
channel #3 is jumpered 5v Bipolar.
The device support can then set default EGUF and EGUL values that will
automatically work via linconv to convert VAL written in volts to RVAL
which is the 16-bit integer that goes to hardware.
If the database designer wants to layer a more meaningful value over the
volts (ie degrees) then they create another database CALC record that
set the volts in the AO record.

As Mark pointed out, this is generally the way to go.
Note, though, that you don't need the additional CALC record to convert
from something else. Instead of overwriting, Device Support should *use*
the EGUL and EGUF values that the db designer created.

That way an ao with "...@5V BIP" and EGUF/EGUL = +/- 5 will convert from
"output voltage" to the 16-bit integer your card needs, while setting
EGUF/EGUL to something else will do the linear conversion from that
"something else" range to your raw value. This is the whole point of
having EGUF/EGUL/EGU as design fields - the only thing Device Support
has to do is calculate the actual conversion factors, as only the Device
Support reads the jumper info from the OUT link, and knows the bit width
and other particularities of that device.
Please do not write your device support starting from scratch. Copy the
device support for a device that is similar to yours, understand it,
refactor to get all the names right, then apply the changes necessary
for your specific hardware. That way you probably will not only learn a
lot, but also have a better support library in less time.
Good luck!
Ralph

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System