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MPI
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The Motion Programming
Interface (MPI)
defines a set of object-oriented, C-language functions and
data types that you can use to develop motion control applications.
The MPI is designed to be independent of the motion controller
hardware used, as well as the platform (operating system
& compiler) on which the motion control application is built.
To support the MPI, a platform must be 32-bit (e.g. Windows
NT). Most 32-bit platforms are capable of multi-threading
and multi-tasking, and the MPI has built-in features that
simplify the design and development of these types of applications.
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| For
XMP only |
Instructions
for the implementation of MPI in Motion Engineering's
XMP motion controller are flagged with the notice "For
XMP only." |
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To add custom features, applications often make use of extensions
to the MPI, which limits portability.
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Platform
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A platform is the combination of the host computer, operating
system, and C compiler. A platform must be 32-bit, i.e., the
operating system must be able to execute 32-bit programs.
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| For
XMP only |
The MPI/XMP
has been ported to the WindowsNT/Microsoft Visual C++
platform. This platform is referred to as XMP-WinNT. If
you are interested in using the MPI/XMP with other operating
systems and C compilers, please contact MEI. |
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MPI Installation Directory
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The MPI installation directory is the location into which
the MPI software has been installed. The installation procedure
suggests a default location (C:\MEI), but you can choose to
install it wherever you desire. It is highly recommended that
you use the default location. The installation directory contains
an MPI directory:
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MPI Subdirectories
| Directory \ MPI |
Contains |
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\doc
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Documentation - User and Reference
Guides |
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\include
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MPI header files |
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| For
XMP-WinNT only |
The default
installation directory is C:\MEI, and it contains a release
note named YYYYMMDD.pdf, where YYYY represents the year,
MM the month, and DD the day of the release. The installation
directory also contains an XMP directory, which has various
subdirectories. |
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XMP Subdirectories
| Directory:
C:\MEI\XMP |
Contains |
\app
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Sample applications |
\bin
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XMP firmware |
\bin\WinNT
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Windows NT
utilities (from util) |
\doc
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Documentation - XMP Harware
and Software Reference |
\include
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XMP header
files |
\lib
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XMP libraries |
\util
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XMP utility
source |
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Object
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An object is an instance of a data structure. The data structure
is typically not directly accessible by an application.
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(also called a method) to create an object, the function
returns a handle to the object. The object handle is then passed
as the first argument to all other functions (methods) that
are associated with that object. These functions provide indirect
access to the object's data structure. When it is finished using
an object, an application simply calls another function to delete
it. |
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| Example |
The MPI defines
an Axis object. An Axis object is created by the mpiAxisCreate(...)
function, which returns a handle of type MPIAxis. The
mpiAxisStatus(...) function takes an Axis handle as its
first argument and returns the status of the hardware
axis with which the Axis object is associated. An Axis
object is deleted by calling the mpiAxisDelete(...) function. |
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Handle
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A handle is returned by the function that creates an object,
and the handle uniquely identifies that object. A handle is
simply a pointer to a pointer to an object. The MPI defines
the type MPIHandle to be a generic handle. The symbol
MPIHandleVOID is used to represent an invalid handle.
The MPI functions that create and delete objects typically
allocate and free memory from a heap; in this case a handle
is generally a pointer to the allocated object data structure.
However, an MPI implementation could define a handle to be
a pointer into a static array of data structures, or an index
into such an array. Regardless, an
application MUST NOT do anything with a handle other than
to pass it as an argument to other functions. In
cases where a handle is a pointer, the pointer cannot be dereferenced,
because the object data structure to which the handle points
is not directly available to the application.
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| Example |
The MPI defines
an Axis handle to be of type MPIAxis. An axis handle named
axisHandle can be declared as follows: MPIAxis axisHandle;
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Method
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A function associated with an object is called a method.
The first argument of a method is always the handle of the
object with which it is associated. A function that is not
associated with an object is called a function. Throughout
the MPI documentation, the term function refers to
methods and functions, whereas the term method only
refers to methods.
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| Example |
The following
functions are all considered to be methods: mpiAxisCreate(...),
mpiAxisStatus(...), mpiAxisDelete(...). Except for mpiAxisCreate(...),
these functions all take an MPIAxis handle as their first
argument. |
MPIAxis axis;
axis = mpiAxisCreate(.);
mpiAxisStatus(axis, .);
mpiAxisDelete(axis);
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Module
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A module is a source file (module.c) whose interface
is declared in a header file (module.h). A module contains
code symbols (methods, functions, macros) and data symbols
(data, data types and constants) that together implement an
object. However, a module may also contain functions that
have a logical connection without being associated with an
object.
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| MPI Module |
Header |
| Adc |
adc.h |
| Axis |
axis.h |
| Capture |
capture.h |
| Command |
command.h |
| Control |
control.h |
| Event |
event.h |
| EventMgr |
eventmgr.h |
| Filter |
filter.h |
| Idn |
idn.h |
| IdnList |
idnlist.h |
| Message |
message.h |
| Motion |
motion.h |
| Motor |
motor.h |
| MpiDef |
mpidef.h |
| Node |
node.h |
| Notify |
notify.h |
| Object |
object.h |
| Recorder |
recorder.h |
| Sequence |
sequence.h |
| Sercos |
sercos.h |
| StdMpi |
stdmpi.h |
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| XMP Module |
Header |
| Client |
client.h |
| Element |
element.h |
| Firmware |
firmware.h |
| Flash |
flash.h |
| List |
list.h |
| Map |
map.h |
| MeiDef |
meidef.h |
| Packet |
packet.h |
| Platform |
platform.h |
| Remove |
remove.h |
| RipTide |
riptide.h |
| Server |
server.h |
| Trace |
trace.h |
| XMP |
xmp.h |
| Utility Module |
Header |
| msgCHECK |
msg.h |
| Service |
service.h |
| Log |
log.h |
| LogFunc |
logFunc.h |
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| Example |
The axis module consists
of a source file called axis.c and a header file
called axis.h. The axis.c source file contains
the definitions of all Axis code and data symbols, in
particular the Axis object data structure. The axis.h
header file contains the declarations for the code and
data symbols in axis.c. |
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