Rice Lake iRite IDE - Manual (Page 7)

920i Programming Reference - Introduction 3
For example, the built-in intrinsic function of the
UNITS key is to switch between primary, secondary,
and tertiary units. If the handler UnitsKeyPressed was
defined in a user program, then the UNITS key no
longer switches between primary, secondary, and
tertiary units, but instead does whatever is written in
the handler
UnitsKeyPressed . The ability to turn off the
custom event handler and return to the intrinsic
functionality is provided by the
DisableHandler
function.
It is important to note that only one event handler can
be running at a time. This means that if an event
occurs while another event handler is running, the
new event will not be serviced immediately but
instead will be placed in a queue and serviced after the
current event is done executing.
This means that if you are executing within an infinite
loop in an event handler, then no other event handlers
will ever get serviced. This doesn’t mean that the
indicator will be totally locked-up: The
920i will still
be executing its other tasks, like calculating current
weights, and running the setpoint engine. But it will
not run any other custom event handlers while one
event is executing in an infinite loop.
There are some fatal errors that an iRite program can
make that will completely disable the 920i . Some of
these errors are "…divide by zero", "string space
exhausted", and "array bounds violation". When they
occur, the
920i stops processing and displays a fatal
error message on the display. Power must be cycled to
reset the indicator.
After the indicator has been restarted, it should be put
into setup mode, and a new version (without the fatal
error) of the
iRite program should be loaded. If you
are unfortunate enough to program a fatal error in
your ProgramStartup Handler, then cycling power to
the unit will only cause the ProgramStartup Handler to
be run again and repeat the fatal error.
I n t h i s c a s e y o u m u s t p e r f o r m a
RESETCONFIGURATION. Your program, along
with the configuration, will be erased and set to the
defaults. This will allow you to reload your
iRite
program after you have corrected the code that
generated the fatal error and re-compiled the program.
1.5 Sound Programming Practices
The most important thing to remember about writing
sou rce code is that it has two v ery important
f u n c t i o n s : i t m u s t w o r k , a n d i t m u s t c l e a r l y
communicate how it works. At first glance, especially
to a beginning programmer, it may seem that getting
the program to work is more important than clearly
commenting and documenting how it works.
As a professional programmer, you will realize that a
higher quality product is produced, which is less
costly to maintain, when the source code is well
d o c u m e n t e d . Yo u , s o m e b o d y e l s e a t y o u r
organization, the customer, or RLWS Support
Personnel, may need to look at some
iRite source
code, months or years from now, long after the
original author has forgotten how the program worked
or isn’t around to ask. This is why we advocate
programming to a specific standard. The template
programs, example programs, and purchased custom
programs that are available from RLWS follow a
single standard. You are welcome to download this
standard from our website, or you can write your own.
The purpose of a standard is to document the way all
programmers will create software for the
920i
indicator. When the standard is followed, the source
code will be easy to follow and understand. The
standard will document: the recommended style and
form for module, program, and subprogram headers,
p rop er n am ing co nv en tions for variables and
functions, guidelines for function size and purpose,
commenting guidelines, and coding conventions.