halmodule.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/
\lyxformat 221
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\layout Chapter

Creating Userspace Python Components with the 'hal' module
\layout Section

Basic usage
\layout Standard

A userspace component begins by creating its pins and parameters, then enters
 a loop which will periodically drive all the outputs from the inputs.
 The following component copies the value seen on its input pin (
\family typewriter 
passthrough.in
\family default 
) to its output pin (
\family typewriter 
passthrough.out
\family default 
) approximately once per second.
\layout LyX-Code

#!/usr/bin/python
\newline 
import hal, time
\newline 
h = hal.component("passthrough")
\newline 
h.newpin("in", hal.HAL_FLOAT, hal.HAL_IN)
\newline 
h.newpin("out", hal.HAL_FLOAT, hal.HAL_OUT)
\newline 
h.ready()
\newline 
try:
\newline 
    while 1:
\newline 
        time.sleep(1)
\newline 
        h['out'] = h['in']
\newline 
except KeyboardInterrupt:
\newline 
    raise SystemExit
\layout Standard

Copy the above listing into a file named 
\begin_inset Quotes eld
\end_inset 

passthrough
\begin_inset Quotes erd
\end_inset 

, make it executable (
\family typewriter 
chmod +x), 
\family default 
and place it on your 
\family typewriter 
$PATH
\family default 
.
 Then try it out:
\layout LyX-Code

$ halrun
\newline 
halcmd: loadusr passthrough
\newline 
halcmd: show pin
\newline 
Component Pins:
\newline 
Owner  Type  Dir     Value      Name
\newline 
 03    float IN              0  passthrough.in
\newline 
 03    float OUT             0  passthrough.out
\newline 
halcmd: setp passthrough.in 3.14
\newline 
halcmd: show pin
\newline 
Component Pins:
\newline 
Owner  Type  Dir     Value      Name
\newline 
 03    float IN           3.14  passthrough.in
\newline 
 03    float OUT          3.14  passthrough.out
\layout Section

Userspace components and delays
\layout Standard

If you typed 
\begin_inset Quotes eld
\end_inset 

show pin
\begin_inset Quotes erd
\end_inset 

 quickly, you may see that 
\family typewriter 
passthrough.out
\family default 
 still had its old value of 0.
 This is because of the call to 'time.sleep(1)', which makes the assignment
 to the output pin occur at most once per second.
 Because this is a userspace component, the actual delay between assignments
 can be much longer--for instance, if the memory used by the passthrough
 component is swapped to disk, the assignment could be delayed until that
 memory is swapped back in.
\layout Standard

Thus, userspace components are suitable for user-interactive elements such
 as control panels (delays in the range of milliseconds are not noticed,
 and longer delays are acceptable), but not for sending step pulses to a
 stepper driver board (delays must always be in the range of microseconds,
 no matter what).
\layout Section

Create pins and parameters
\layout LyX-Code

h = hal.component("passthrough")
\layout Standard

The component itself is created by a call to the constructor '
\family typewriter 
hal.component
\family default 
'.
 The arguments are the HAL component name and (optionally) the prefix used
 for pin and parameter names.
 If the prefix is not specified, the component name is used.
\layout LyX-Code

h.newpin("in", hal.HAL_FLOAT, hal.HAL_IN)
\layout Standard

Then pins are created by calls to methods on the component object.
 The arguments are: pin name suffix, pin type, and pin direction.
 For parameters, the arguments are: parameter name suffix, parameter type,
 and parameter direction.
\layout Standard


\begin_inset Float table
wide false
collapsed false

\layout Caption

HAL Option Names
\layout Standard


\begin_inset  Tabular
<lyxtabular version="3" rows="3" columns="5">
<features>
<column alignment="center" valignment="top" leftline="true" width="0">
<column alignment="center" valignment="top" leftline="true" width="0">
<column alignment="center" valignment="top" leftline="true" width="0">
<column alignment="center" valignment="top" leftline="true" width="0">
<column alignment="center" valignment="top" leftline="true" rightline="true" width="0">
<row topline="true">
<cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none">
\begin_inset Text

\layout Standard


\series bold 
Pin and Parameter Types:
\end_inset 
</cell>
<cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none">
\begin_inset Text

\layout Standard

HAL_BIT
\end_inset 
</cell>
<cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none">
\begin_inset Text

\layout Standard

HAL_FLOAT
\end_inset 
</cell>
<cell alignment="center" valignment="top" topline="true" leftline="true" rightline="true" usebox="none">
\begin_inset Text

\layout Standard

HAL_S32
\end_inset 
</cell>
<cell alignment="center" valignment="top" topline="true" leftline="true" rightline="true" usebox="none">
\begin_inset Text

\layout Standard

HAL_U32
\end_inset 
</cell>
</row>
<row topline="true">
<cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none">
\begin_inset Text

\layout Standard


\series bold 
Pin Directions:
\end_inset 
</cell>
<cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none">
\begin_inset Text

\layout Standard

HAL_IN
\end_inset 
</cell>
<cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none">
\begin_inset Text

\layout Standard

HAL_OUT
\end_inset 
</cell>
<cell alignment="center" valignment="top" topline="true" leftline="true" rightline="true" usebox="none">
\begin_inset Text

\layout Standard

HAL_IO
\end_inset 
</cell>
<cell alignment="center" valignment="top" topline="true" leftline="true" rightline="true" usebox="none">
\begin_inset Text

\layout Standard

\end_inset 
</cell>
</row>
<row topline="true" bottomline="true">
<cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none">
\begin_inset Text

\layout Standard


\series bold 
Parameter Directions:
\end_inset 
</cell>
<cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none">
\begin_inset Text

\layout Standard

HAL_RO
\end_inset 
</cell>
<cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none">
\begin_inset Text

\layout Standard

HAL_RW
\end_inset 
</cell>
<cell alignment="center" valignment="top" topline="true" leftline="true" rightline="true" usebox="none">
\begin_inset Text

\layout Standard

\end_inset 
</cell>
<cell alignment="center" valignment="top" topline="true" leftline="true" rightline="true" usebox="none">
\begin_inset Text

\layout Standard

\end_inset 
</cell>
</row>
</lyxtabular>

\end_inset 


\end_inset 


\layout Standard

The full pin or parameter name is formed by joining the prefix and the suffix
 with a 
\begin_inset Quotes eld
\end_inset 

.
\begin_inset Quotes erd
\end_inset 

, so in the example the pin created is called 
\family typewriter 
passthrough.in
\family default 
.
\layout LyX-Code

h.ready()
\layout Standard

Once all the pins and parameters have been created, call the 
\family typewriter 
.ready()
\family default 
 method.
\layout Subsection

Changing the prefix
\layout Standard

The prefix can be changed by calling the 
\family typewriter 
.setprefix()
\family default 
 method.
 The current prefix can be retrieved by calling the 
\family typewriter 
.getprefix()
\family default 
 method.
\layout Section

Reading and writing pins and parameters
\layout Standard

For pins and parameters which are also proper Python identifiers, the value
 may be accessed or set using the attribute syntax:
\layout LyX-Code

h.out = h.in
\layout Standard

For all pins, whether or not they are also proper Python identifiers, the
 value may be accessed or set using the subscript syntax:
\layout LyX-Code

h['out'] = h['in']
\layout Subsection

Driving output (HAL_OUT) pins
\layout Standard

Periodically, usually in response to a timer, all HAL_OUT pins should be
 
\begin_inset Quotes eld
\end_inset 

driven
\begin_inset Quotes erd
\end_inset 

 by assigning them a new value.
 This should be done whether or not the value is different than the last
 one assigned.
 When a pin is connected to a signal, its old output value is not copied
 into the signal, so the proper value will only appear on the signal once
 the component assigns a new value.
\layout Subsection

Driving bidirectional (HAL_IO) pins
\layout Standard

The above rule does not apply to bidirectional pins.
 Instead, a bidirectional pin should only be driven by the component when
 the component wishes to change the value.
 For instance, in the canonical encoder interface, the encoder component
 only sets the 
\series bold 
index-enable
\series default 
 pin to 
\series bold 
FALSE
\series default 
 (when an index pulse is seen and the old value is 
\series bold 
TRUE
\series default 
), but never sets it to 
\series bold 
TRUE
\series default 
.
 Repeatedly driving the pin 
\series bold 
FALSE
\series default 
 might cause the other connected component to act as though another index
 pulse had been seen.
\layout Section

Exiting
\layout Standard

A 
\begin_inset Quotes eld
\end_inset 


\family typewriter 
halcmd unload
\family default 

\begin_inset Quotes erd
\end_inset 

 request for the component is delivered as a 
\family typewriter 
KeyboardInterrupt
\family default 
 exception.
 When an unload request arrives, the process should either exit in a short
 time, or call the 
\family typewriter 
.exit()
\family default 
 method on the component if substantial work (such as reading or writing
 files) must be done to complete the shutdown process.
\layout Section

Project ideas
\layout Itemize

Create an external control panel with buttons, switches, and indicators.
 Connect everything to a microcontroller, and connect the microcontroller
 to the PC using a serial interface.
 Python has a very capable serial interface module called 
\begin_inset LatexCommand \url[pyserial]{http://pyserial.sourceforge.net/}

\end_inset 

 (Ubuntu package name 
\begin_inset Quotes eld
\end_inset 

python-serial
\begin_inset Quotes erd
\end_inset 

, in the universe repository)
\layout Itemize

Attach a 
\begin_inset LatexCommand \url[LCDProc]{http://lcdproc.omnipotent.net/}

\end_inset 

-compatible LCD module and use it to display a digital readout with information
 of your choice (Ubuntu package name 
\begin_inset Quotes eld
\end_inset 

lcdproc
\begin_inset Quotes erd
\end_inset 

, in the universe repository)
\layout Itemize

Create a virtual control panel using any GUI library supported by Python
 (gtk, qt, wxwindows, etc)
\the_end