intro.lyx

CNC 的开放码,EMC2 V2.2.8版

iocontrol
\begin_inset LatexCommand \index{iocontrol}

\end_inset 

 A user space module that accepts NML I/O commands and interacts with HAL
 
\layout Description

classicladder
\begin_inset LatexCommand \index{ClassicLadder}

\end_inset 

 A PLC using HAL for all I/O
\layout Description

halui
\begin_inset LatexCommand \index{halui}

\end_inset 

 A user space program that interacts with HAL and sends NML commands, it
 is intended to work as a full User Interface using external knobs & switches
 
\layout Subsection


\begin_inset LatexCommand \label{sub:InternalComponents}

\end_inset 

Internal Components
\layout Description

stepgen
\begin_inset LatexCommand \index{stepgen}

\end_inset 

 Software step pulse generator with position loop.
 See section 
\begin_inset LatexCommand \ref{sec:Stepgen}

\end_inset 


\layout Description

encoder
\begin_inset LatexCommand \index{encoder}

\end_inset 

 Software based encoder counter.
 See section 
\begin_inset LatexCommand \ref{sec:Encoder}

\end_inset 


\layout Description

pid
\begin_inset LatexCommand \index{pid}

\end_inset 

 Proportional/Integral/Derivative control loops.
 See section 
\begin_inset LatexCommand \ref{sec:PID}

\end_inset 


\layout Description

siggen
\begin_inset LatexCommand \index{siggen}

\end_inset 

 A sine/cosine/triangle/square wave generator for testing.
 See section 
\begin_inset LatexCommand \ref{sec:Siggen}

\end_inset 


\layout Description

supply
\begin_inset LatexCommand \index{supply}

\end_inset 

 a simple source for testing
\layout Description

blocks
\begin_inset LatexCommand \index{blocks}

\end_inset 

 assorted useful components (mux, demux, or, and, integ, ddt, limit, wcomp,
 etc.)
\layout Subsection


\begin_inset LatexCommand \label{sub:HardwareDrivers}

\end_inset 

Hardware Drivers
\layout Description

hal_ax5214h
\begin_inset LatexCommand \index{hal-ax5214h}

\end_inset 

 A driver for the Axiom Measurement & Control AX5241H digital I/O board
\layout Description

hal_m5i20
\begin_inset LatexCommand \index{hal-m5i20}

\end_inset 

 Mesa Electronics 5i20 board
\layout Description

hal_motenc
\begin_inset LatexCommand \index{hal-motenc}

\end_inset 

 Vital Systems MOTENC-100 board
\layout Description

hal_parport
\begin_inset LatexCommand \index{hal-parport}

\end_inset 

 PC parallel port.
 See section 
\begin_inset LatexCommand \ref{sec:Parport}

\end_inset 


\layout Description

hal_ppmc
\begin_inset LatexCommand \index{hal-ppmc}

\end_inset 

 Pico Systems family of controllers (PPMC, USC and UPC)
\layout Description

hal_stg
\begin_inset LatexCommand \index{hal-stg}

\end_inset 

 Servo To Go card (version 1 & 2)
\layout Description

hal_vti
\begin_inset LatexCommand \index{hal-vti}

\end_inset 

 Vigilant Technologies PCI ENCDAC-4 controller
\layout Subsection


\begin_inset LatexCommand \label{sub:ToolsUtilities}

\end_inset 

Tools and Utilities
\layout Description

halcmd
\begin_inset LatexCommand \index{halcmd}

\end_inset 

 Command line tool for configuration and tuning.
 See section 
\begin_inset LatexCommand \ref{sec:Halcmd}

\end_inset 

 
\layout Description

halgui GUI tool for configuration and tuning (not implemented yet).
\layout Description

halmeter
\begin_inset LatexCommand \index{halmeter}

\end_inset 

 A handy multimeter for HAL signals.
 See section 
\begin_inset LatexCommand \ref{sec:Halmeter}

\end_inset 


\layout Description

halscope
\begin_inset LatexCommand \index{halscope}

\end_inset 

 A full featured digital storage oscilloscope for HAL signals.
 See section 
\begin_inset LatexCommand \ref{sec:Halscope}

\end_inset 


\layout Standard

Each of these building blocks is described in detail in later chapters.
 
\layout Section


\begin_inset LatexCommand \label{sec:Tinkertoys}

\end_inset 

Tinkertoys, Erector Sets, Legos and the HAL
\layout Standard

A first introduction to HAL concepts can be mind boggling.
 Building anything with blocks can be a challenge but some of the toys that
 we played with as kids can be an aid to building things with the HAL.
\layout Subsection

Tower
\layout Quote

I'm watching as my son and his six year old daughter build a tower from
 a box full of random sized blocks, rods, jar lids and such.
 The aim is to see how tall they can make the tower.
 The narrower the base the more blocks left to stack on top.
 But the narrower the base, the less stable the tower.
 I see them studying both the next block and the shelf where they want to
 place it to see how it will balance out with the rest of the tower.
 
\layout Standard

The notion of stacking cards to see how tall you can make a tower is a very
 old and honored way of spending spare time.
 At first read, the integrator may have gotten the impression that building
 a HAL was a bit like that.
 It can be but with proper planning an integrator can build a stable system
 as complex as the machine at hand requires.
 
\layout Subsection

Erector Sets
\begin_inset Foot
collapsed false

\layout Standard

The Erector Set was an invention of AC Gilbert
\end_inset 


\layout Standard

What was great about the sets was the building blocks, metal struts and
 angles and plates, all with regularly spaced holes.
 You could design things and hold them together with the little screws and
 nuts.
 
\layout Quote

I got my first erector set for my fourth birthday.
 I know the box suggested a much older age than I was.
 Perhaps my father was really giving himself a present.
 I had a hard time with the little screws and nuts.
 I really needed four arms, one each for the screwdriver, screw, parts to
 be bolted together, and nut.
 Perseverence, along with father's eventual boredom, got me to where I had
 built every project in the booklet.
 Soon I was lusting after the bigger sets that were also printed on that
 paper.
 Working with those regular sized pieces opened up a world of construction
 for me and soon I moved well beyond the illustrated projects.
 
\layout Standard

Hal components are not all the same size and shape but they allow for grouping
 into larger units that will do useful work.In this sense they are like the
 parts of an Erector set.
 Some components are long and thin.
 They essentially connect high level commands to specific physical pins.
 Other components are more like the rectangular platforms upon which whole
 machines could be built.
 An integrator will quickly get beyond the brief examples and begin to bolt
 together components in ways that are unique to them.
\layout Subsection

Tinkertoys
\begin_inset Foot
collapsed false

\layout Standard

Tinkertoy is now a registered trademark of the Hasbro company.
\end_inset 


\layout Quote

Wooden Tinker toys had a more humane feel that the cold steel of Erector
 Sets.
 The heart of construction with Tinker Toys was a round connector with eight
 holes equally spaced around the circumference.
 It also had a hole in the center that was perpendicular to all the holes
 around the hub.
\layout Quote

Hubs were connected with rods of several different lengths.
 Builders would make large wheels by using these rods as spokes sticking
 out from the center hub.
 
\layout Quote

My favorite project was a rotating space station.
 Short spokes radiated from all the holes in the center hub and connected
 with hubs on the ends of each spoke.
 These outer hubs were connected to each other with longer spokes.
 I'd spend hours dreaming of living in such a device, walking from hub to
 hub around the outside as it slowly rotated producing near gravity in weightles
s space.
 Supplies traveled through the spokes in elevators that transfered them
 to an from rockets docked at the center hub while they transfered their
 precious cargos.
\layout Standard

The idea of one pin or component being the hub for many connections is also
 an easy concept within the HAL.
 Examples two and four (see section 
\begin_inset LatexCommand \ref{cha:HAL-Tutorial}

\end_inset 

) connect the meter and scope to signals that are intended to go elsewhere.
 Less easy is the notion of a hub for several incoming signals but that
 is also possible with proper use of functions within that hub component
 that handle those signals as they arrive from other components.
\layout Standard

Another thought that comes forward from this toy is a mechanical representation
 of HAL threads.
 A thread might look a bit like a centipede, caterpillar, or earwig.
 A backbone of hubs, HAL components, strung together with rods, HAL signals.
 Each component takes in it own parameters and input pins and passes on
 output pins and parameters to the next component.
 Signals travel along the backbone from end to end and are added to or modified
 by each component in turn.
 
\layout Standard

Threads are all about timing and doing a set of tasks from end to end.
 A mechanical representation is available with Tinkertoys also when we think
 of the length of the toy as a measure of the time taken to get from one
 end to the other.
 A very different thread or backbone is created by connecting the same set
 of hubs with different length rods.
 The total length of the backbone can be changed by the length of rods used
 to connect the hubs.
 The order of operations is the same but the time to get from beginning
 to end is very diferent.
 
\layout Subsection


\begin_inset LatexCommand \label{sub:A-Lego-Example}

\end_inset 

A Lego Example
\begin_inset Foot
collapsed true

\layout Standard

The Lego name is a trademark of the Lego company.
 
\end_inset 


\layout Standard

When Lego blocks first arrived in our stores they were pretty much all the
 same size and shape.
 Sure there were half sized one and a few quarter sized as well but that
 rectangular one did most of the work.
 Lego blocks interconnected by snapping the holes in the underside of one
 onto the pins that stuck up on another.
 By overlapping layers, the joints between could be made very strong, even
 around corners or tees.
 
\layout Quote

I watched my children and grandchildren build with legos -- the same legos.
 There are a few thousand of them in an old ratty but heavy duty cardboard
 box that sits in a corner of the recreation room.
 It stays there in the open because it was too much trouble to put the box
 away and then get it back out for every visit and it is always used during
 a visit.
 There must be Lego parts in there from a couple dozen different sets.
 The little booklets that came with them are long gone but the magic of
 building with interlocking pieces all the same size is something to watch.
 
\layout Section


\begin_inset LatexCommand \label{sec:Timing-Issues}

\end_inset 

Timing Issues In HAL
\layout Standard

Unlike the physical wiring models between black boxes that we have said
 that HAL is based upon, simply connecting two pins with a hal-signal falls
 far short of the action of the physical case.
 
\layout Standard

True relay logic consists of relays connected together, and when a contact
 opens or closes, current flows (or stops) immediately.
 Other coils may change state, etc, and it all just "happens".
 But in PLC style ladder logic, it doesn't work that way.
 Usually in a single pass through the ladder, each rung is evaluated in
 the order in which it appears, and only once per pass.
 A perfect example is a single rung ladder, with a NC contact in series
 with a coil.
 The contact and coil belong to the same relay.
 
\layout Standard

If this were a conventional relay, as soon as the coil is energized, the
 contacts begin to open and de-energize it.
 That means the contacts close again, etc, etc.
 The relay becomes a buzzer.
\layout Standard

With a PLC, if the coil is OFF and the contact is closed when the PLC begins
 to evaluate the rung, then when it finishes that pass, the coil is ON.
 The fact that turning on the coil opens the contact feeding it is ignored
 until the next pass.
 On the next pass, the PLC sees that the contact is open, and de-energizes
 the coil.
 So the relay still switches rapidly between on and off, but at a rate determine
d by how often the PLC evaluates the rung.
 
\layout Standard

In HAL, the function is the code that evaluates the rung(s).
 In fact, the HAL-aware realtime version of ClassicLadder exports a function
 to do exactly that.
 Meanwhile, a thread is the thing that runs the function at specific time
 intervals.
 Just like you can choose to have a PLC evaluate all its rungs every 10mS,
 or every second, you can define HAL threads with different periods.
\layout Standard

What distinguishes one thread from another is 
\emph on 
not
\emph default 
 what the thread does - that is determined by which functions are connected
 to it.
 The real distinction is simply how often a thread runs.
\layout Standard

In EMC you might have a 50
\begin_inset Formula $\mu$
\end_inset 

s thread and a 1ms thread.
 These would be created baseds on BASE_PERIOD and SERVO_PERIOD--the actual
 times depend on the ini.
\layout Standard

The next step is to decide what each thread needs to do.
 Some of those decisions are the same in (nearly) any emc system--For instance,
 motion-command-handler is always added to servo-thread.
\layout Standard

Other connections would be made by the integrator.
 These might include hooking the STG driver's encoder read and DAC write
 functions to the servo thread, or hooking stepgen's function to the base-thread
, along with the parport function(s) to write the steps to the port.
\the_end