intro.lyx

CNC 的开放码,EMC2 V2.2.8版

#LyX 1.3 created this file. For more info see http://www.lyx.org/
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\layout Chapter


\begin_inset LatexCommand \label{cha:Introduction}

\end_inset 

Introduction
\layout Section


\begin_inset LatexCommand \label{sec:What-is-HAL?}

\end_inset 

What is HAL?
\layout Standard

HAL
\begin_inset LatexCommand \index{HAL}

\end_inset 

 stands for Hardware Abstraction Layer.
 At the highest level, it is simply a way to allow a number of 
\begin_inset Quotes eld
\end_inset 

building blocks
\begin_inset Quotes erd
\end_inset 

 to be loaded and interconnected to assemble a complex system.
 The 
\begin_inset Quotes eld
\end_inset 

Hardware
\begin_inset Quotes erd
\end_inset 

 part is because HAL was originally designed to make it easier to configure
 EMC for a wide variety of hardware devices.
 Many of the building blocks are drivers for hardware devices.
 However, HAL can do more than just configure hardware drivers.
\layout Subsection

HAL is based on traditional system design techniques
\layout Standard

HAL is based on the same principles that are used to design hardware circuits
 and systems, so it is useful to examine those principles first.
\layout Standard

Any system (including a CNC
\begin_inset LatexCommand \index{CNC}

\end_inset 

 machine), consists of interconnected components.
 For the CNC machine, those components might be the main controller, servo
 amps or stepper drives, motors, encoders, limit switches, pushbutton pendants,
 perhaps a VFD for the spindle drive, a PLC to run a toolchanger, etc.
 The machine builder must select, mount and wire these pieces together to
 make a complete system.
\layout Subsubsection

Part Selection
\layout Standard

The machine builder does not need to worry about how each individual part
 works.
 He treats them as black boxes.
 During the design stage, he decides which parts he is going to use - steppers
 or servos, which brand of servo amp, what kind of limit switches and how
 many, etc.
 The integrator's decisions about which specific components to use is based
 on what that component does and the specifications supplied by the manufacturer
 of the device.
 The size of a motor and the load it must drive will affect the choice of
 amplifier needed to run it.
 The choice of amplifier may affect the kinds of feedback needed by the
 amp and the velocity or position signals that must be sent to the amp from
 a control.
 
\layout Standard

In the HAL world, the integrator must decide what HAL components are needed.
 Usually every interface card will require a driver.
 Additional components may be needed for software generation of step pulses,
 PLC functionality, and a wide variety of other tasks.
\layout Subsubsection

Interconnection Design
\layout Standard

The designer of a hardware system not only selects the parts, he also decides
 how those parts will be interconnected.
 Each black box has terminals, perhaps only two for a simple switch, or
 dozens for a servo drive or PLC.
 They need to be wired together.
 The motors connect to the servo amps, the limit switches connect to the
 controller, and so on.
 As the machine builder works on the design, he creates a large wiring diagram
 that shows how all the parts should be interconnected.
\layout Standard

When using HAL, components are interconnected by signals.
 The designer must decide which signals are needed, and what they should
 connect.
\layout Subsubsection

Implementation
\layout Standard

Once the wiring diagram is complete it is time to build the machine.
 The pieces need to be acquired and mounted, and then they are interconnected
 according to the wiring diagram.
 In a physical system, each interconnection is a piece of wire that needs
 to be cut and connected to the appropriate terminals.
\layout Standard

HAL provides a number of tools to help 
\begin_inset Quotes eld
\end_inset 

build
\begin_inset Quotes erd
\end_inset 

 a HAL system.
 Some of the tools allow you to 
\begin_inset Quotes eld
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connect
\begin_inset Quotes erd
\end_inset 

 (or disconnect) a single 
\begin_inset Quotes eld
\end_inset 

wire
\begin_inset Quotes erd
\end_inset 

.
 Other tools allow you to save a complete list of all the parts, wires,
 and other information about the system, so that it can be 
\begin_inset Quotes eld
\end_inset 

rebuilt
\begin_inset Quotes erd
\end_inset 

 with a single command.
\layout Subsubsection

Testing
\layout Standard

Very few machines work right the first time.
 While testing, the builder may use a meter to see whether a limit switch
 is working or to measure the DC voltage going to a servo motor.
 He may hook up an oscilloscope to check the tuning of a drive, or to look
 for electrical noise.
 He may find a problem that requires the wiring diagram to be changed; perhaps
 a part needs to be connected differently or replaced with something completely
 different.
\layout Standard

HAL provides the software equivalents of a voltmeter, oscilloscope, signal
 generator, and other tools needed for testing and tuning a system.
 The same commands used to build the system can be used to make changes
 as needed.
\layout Subsection

Summary
\layout Standard

This document is aimed at people who already know how to do this kind of
 hardware system integration, but who do not know how to connect the hardware
 to EMC.
\layout Standard

The traditional hardware design as described above ends at the edge of the
 main control.
 Outside the control are a bunch of relatively simple boxes, connected together
 to do whatever is needed.
 Inside, the control is a big mystery -- one huge black box that we hope
 works.
\layout Standard

HAL extends this traditional hardware design method to the inside of the
 big black box.
 It makes device drivers and even some internal parts of the controller
 into smaller black boxes that can be interconnected and even replaced just
 like the external hardware.
 It allows the 
\begin_inset Quotes eld
\end_inset 

system wiring diagram
\begin_inset Quotes erd
\end_inset 

to show part of the internal controller, rather than just a big black box.
 And most importantly it allows the integrator to test and modify the controller
 using the same methods he would use on the rest of the hardware.
\layout Standard

Terms like motors, amps, and encoders are familiar to most machine integrators.
 When we talk about using extra flexible eight conductor shielded cable
 to connect an encoder to the servo input board in the computer, the reader
 immediately understands what it is and is led to the question, 
\begin_inset Quotes eld
\end_inset 

what kinds of connectors will I need to make up each end.
\begin_inset Quotes erd
\end_inset 

 The same sort of thinking is essential for the HAL but the specific train
 of thought may take a bit to get on track.
 Using HAL words may seem a bit strange at first, but the concept of working
 from one connection to the next is the same.
\layout Standard

This idea of extending the wiring diagram to the inside of the controller
 is what HAL is all about.
 If you are comfortable with the idea of interconnecting hardware black
 boxes, you will probably have little trouble using HAL to interconnect
 software black boxes.
\layout Section


\begin_inset LatexCommand \label{sec:HAL-Concepts}

\end_inset 

HAL Concepts
\layout Standard

This section is a glossary that defines key HAL terms but it is a bit different
 than a traditional glossary because these terms are not arranged in alphabetica
l order.
 They are arranged by their relationship or flow in the HAL way of things.
 
\layout Description

Component
\begin_inset LatexCommand \index{HAL Component}

\end_inset 

: When we talked about hardware design, we referred to the individual pieces
 as "parts", "building blocks", "black boxes", etc.
 The HAL equivalent is a "component" or "HAL component".
 (This document uses "HAL component" when there is likely to be confusion
 with other kinds of components, but normally just uses "component".) A HAL
 component is a piece of software with well-defined inputs, outputs, and
 behavior, that can be installed and interconnected as needed.
 
\layout Description

Parameter
\begin_inset LatexCommand \index{HAL Parameter}

\end_inset 

: Many hardware components have adjustments that are not connected to any
 other components but still need to be accessed.
 For example, servo amps often have trim pots to allow for tuning adjustments,
 and test points where a meter or scope can be attached to view the tuning
 results.
 HAL components also can have such items, which are referred to as "parameters".
 There are two types of parameters: Input parameters are equivalent to trim
 pots - they are values that can be adjusted by the user, and remain fixed
 once they are set.
 Output parameters cannot be adjusted by the user - they are equivalent
 to test points that allow internal signals to be monitored.
\layout Description

Pin
\begin_inset LatexCommand \index{HAL Pin}

\end_inset 

: Hardware components have terminals which are used to interconnect them.
 The HAL equivalent is a "pin" or "HAL pin".
 ("HAL pin" is used when needed to avoid confusion.) All HAL pins are named,
 and the pin names are used when interconnecting them.
 HAL pins are software entities that exist only inside the computer.
 
\layout Description

Physical_Pin
\begin_inset LatexCommand \index{HAL Physical-Pin}

\end_inset 

: Many I/O devices have real physical pins or terminals that connect to
 external hardware, for example the pins of a parallel port connector.
 To avoid confusion, these are referred to as "physical pins".
 These are the things that 
\begin_inset Quotes eld
\end_inset 

stick out
\begin_inset Quotes erd
\end_inset 

 into the real world.
\begin_inset Note
collapsed true

\layout Standard

Might need some explanation how HAL_pins and Physical pin relates to something
 like an encoder chip or an stg card.
 We are dealing in data type interface and data type translation/conversion
 here.
 
\end_inset 


\layout Description

Signal
\begin_inset LatexCommand \index{HAL Signal}

\end_inset 

: In a physical machine, the terminals of real hardware components are interconn
ected by wires.
 The HAL equivalent of a wire is a "signal" or "HAL signal".
 HAL signals connect HAL pins together as required by the machine builder.
 HAL signals can be disconnected and reconnected at will (even while the
 machine is running).
\layout Description

Type
\begin_inset LatexCommand \index{HAL Type}

\end_inset 

: When using real hardware, you would not connect a 24 volt relay output
 to the +/-10V analog input of a servo amp.
 HAL pins have the same restrictions, which are based upon their type.
 Both pins and signals have types, and signals can only be connected to
 pins of the same type.
 Currently there are 4 types, as follows:
\layout Itemize


\noun on 
bit
\noun default 
 - a single TRUE/FALSE or ON/OFF value
\layout Itemize


\noun on 
float
\noun default 
 - a 32 bit floating point value, with approximately 24 bits of resolution
 and over 200 bits of dynamic range.
\layout Itemize


\noun on 
u32
\noun default 
 - a 32 bit unsigned integer, legal values are 0 to [phone]
\layout Itemize


\noun on 
s32
\noun default 
 - a 32 bit signed integer, legal values are -2147483648 to [phone]
\layout Description


\begin_inset LatexCommand \label{des:Function}

\end_inset 

Function
\begin_inset LatexCommand \index{HAL Function}

\end_inset 

: Real hardware components tend to act immediately on their inputs.
 For example, if the input voltage to a servo amp changes, the output also
 changes automatically.
 However software components cannot act "automatically".
 Each component has specific code that must be executed to do whatever that
 component is supposed to do.
 In some cases, that code simply runs as part of the component.
 However in most cases, especially in realtime components, the code must
 run in a specific sequence and at specific intervals.
 For example, inputs should be read before calculations are performed on
 the input data, and outputs should not be written until the calculations
 are done.
 In these cases, the code is made available to the system in the form of
 one or more "functions".
 Each function is a block of code that performs a specific action.
 The system integrator can use "threads" to schedule a series of functions
 to be executed in a particular order and at specific time intervals.
\layout Description


\begin_inset LatexCommand \label{des:Thread}

\end_inset 

Thread
\begin_inset LatexCommand \index{HAL Thread}

\end_inset 

: A "thread" is a list of functions that runs at specific intervals as part
 of a realtime task.
 When a thread is first created, it has a specific time interval (period),
 but no functions.
 Functions can be added to the thread, and will be executed in order every
 time the thread runs.
\layout Standard

As an example, suppose we have a parport component named hal_parport.
 That component defines one or more HAL pins for each physical pin.
 The pins are described in that component's doc section: their names, how
 each pin relates to the physical pin, are they inverted, can you change
 polarity, etc.
 But that alone doesn't get the data from the HAL pins to the physical pins.
 It takes code to do that, and that is where functions come into the picture.
 The parport component needs at least two functions: one to read the physical
 input pins and update the HAL pins, the other to take data from the HAL
 pins and write it to the physical output pins.
 Both of these functions are part of the parport driver.
 
\layout Section


\begin_inset LatexCommand \label{sec:Intro-HAL-components}

\end_inset 

HAL components
\layout Standard

Each HAL component is a piece of software with well-defined inputs, outputs,
 and behavior, that can be installed and interconnected as needed.
 This section lists some of the available components and a brief description
 of what each does.
 Complete details for each component are available later in this document.
\layout Subsection


\begin_inset LatexCommand \label{sub:ExternalPrograms}

\end_inset 

External Programs with HAL hooks
\layout Description

motion
\begin_inset LatexCommand \index{motion}

\end_inset 

 A realtime module that accepts NML motion commands and interacts with HAL
 
\layout Description