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>Comedi: The <SPAN
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><I
CLASS="EMPHASIS"
>Control and Measurement Device Interface</I
></SPAN
>
handbook
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><DIV
CLASS="GLOSSARY"
><H1
><A
NAME="COMEDILIB-GLOSSARY"
></A
> Glossary
</H1
><DL
><DT
><A
NAME="API"
></A
><B
> Application Program Interface
</B
></DT
> (API)<DD
><P
>The (documented) set of function calls supported by a particular
application, by which programmers can access the functionality
available in the application.
</P
></DD
><DT
><A
NAME="BUFFER"
></A
><B
>buffer
</B
></DT
><DD
><P
><ACRONYM
CLASS="ACRONYM"
>Comedi</ACRONYM
> uses permanently allocated kernel memory for streaming input
and output to store data that has been measured by a device, but has
not been read by an application. These buffers can be resized by the
Comedilib function <CODE
CLASS="FUNCTION"
>comedi_buffer_XXX()</CODE
> or the
<CODE
CLASS="FUNCTION"
>comedi_config</CODE
>
utility.
</P
></DD
><DT
><A
NAME="BUFFEROVERFLOW"
></A
><B
>buffer overflow
</B
></DT
><DD
><P
>This is an error message that indicates that the driver ran out of
space in a <ACRONYM
CLASS="ACRONYM"
>Comedi</ACRONYM
> buffer to put samples. It means that the application
is not copying data out of the buffer quickly enough. Often, this
problem can be fixed by making the <ACRONYM
CLASS="ACRONYM"
>Comedi</ACRONYM
> buffer larger. See
<CODE
CLASS="FUNCTION"
>comedi_buffer_XXX</CODE
> for more information.
</P
></DD
><DT
><A
NAME="DIFFERENTIALIO"
></A
><B
> Differential IO
</B
></DT
><DD
><P
>...
</P
></DD
><DT
><A
NAME="DMA"
></A
><B
> Direct Memory Access
</B
></DT
> (DMA)<DD
><P
>DMA is a method of transferring data between
a device and the main memory of a computer. DMA operates differently
on ISA and PCI cards. ISA DMA is handled by a controller on the
motherboard and is limited to transfers to/from the lowest 16 MB of
physical RAM and can only handle a single segment of memory at a time.
These limitations make it almost useless. PCI ("bus mastering") DMA
is handled by a controller on the device, and can typically address
4 GB of RAM and handle many segments of memory simultaneously. DMA
is usually not the only means to data transfer, and may or may not
be the optimal transfer mechanism for a particular situation.
</P
></DD
><DT
><A
NAME="FIFO"
></A
><B
> First In, First Out
</B
></DT
> (FIFO)<DD
><P
>Most devices have a limited amount of on-board space to store samples
before they are transferred to the Comedi buffer. This allows the CPU or
DMA controller to do other things, and then efficiently process a
large number of samples simultaneously. It also increases the
maximum interrupt latency that the system can handle without
interruptions in data.
</P
></DD
><DT
><A
NAME="COMEDICOMMAND"
></A
><B
><ACRONYM
CLASS="ACRONYM"
>Comedi</ACRONYM
> command
</B
></DT
><DD
><P
><ACRONYM
CLASS="ACRONYM"
>Comedi</ACRONYM
> commands are the mechanism that applications configure
subdevices for streaming input and output.
</P
></DD
><DT
><A
NAME="COMMAND"
></A
><B
>command
</B
></DT
><DD
><P
><EM
>See: </EM
><A
HREF="g6679.html#COMEDICOMMAND"
><ACRONYM
CLASS="ACRONYM"
>Comedi</ACRONYM
> command
</A
></P
></DD
><DT
><A
NAME="CONFIGOPTION"
></A
><B
>configuration option
</B
></DT
><DD
><P
> </P
></DD
><DT
><A
NAME="INSTRUCTION"
></A
><B
>instruction
</B
></DT
><DD
><P
><ACRONYM
CLASS="ACRONYM"
>Comedi</ACRONYM
> instructions are the mechanism used by applications to do
immediate input from channels, output to channels, and configuration
of subdevices and channels.
</P
></DD
><DT
><A
NAME="INSTRUCTIONLIST"
></A
><B
>instruction list
</B
></DT
><DD
><P
>Instruction lists allow the application to perform multiple <ACRONYM
CLASS="ACRONYM"
>Comedi</ACRONYM
>
instructions in the same system call.
</P
></DD
><DT
><A
NAME="OPTION"
></A
><B
>option
</B
></DT
><DD
><P
> </P
><P
><EM
>See Also: </EM
><A
HREF="g6679.html#OPTIONLIST"
>option list
</A
>.</P
></DD
><DT
><A
NAME="OPTIONLIST"
></A
><B
>option list
</B
></DT
><DD
><P
>Option lists are used with <CODE
CLASS="FUNCTION"
>comedi_config</CODE
> to
perform driver configuration.
</P
><P
><EM
>See Also: </EM
><A
HREF="g6679.html#CONFIGOPTION"
>configuration option
</A
><EM
>, </EM
><A
HREF="g6679.html#OPTION"
>option
</A
>.</P
></DD
><DT
><A
NAME="OVERRUN"
></A
><B
>overrun
</B
></DT
><DD
><P
>This is an error message that indicates that there was device-level
problem, typically with trigger pulses occurring faster than the
board can handle.
</P
></DD
><DT
><A
NAME="POLL"
></A
><B
>poll
</B
></DT
><DD
><P
>The term poll (and polling) is used for several different related
concepts in <ACRONYM
CLASS="ACRONYM"
>Comedi</ACRONYM
>. <ACRONYM
CLASS="ACRONYM"
>Comedi</ACRONYM
> implements the
<CODE
CLASS="FUNCTION"
>poll()</CODE
> system call for Comedi devices, which is
similar to <CODE
CLASS="FUNCTION"
>select()</CODE
>, and returns information
about file descriptors that can be read or written. Comedilib also
has a function called <CODE
CLASS="FUNCTION"
>comedi_poll()</CODE
>, which causes
the driver to copy all available data from the device to the <ACRONYM
CLASS="ACRONYM"
>Comedi</ACRONYM
>
buffer. In addition, some drivers may use a polling technique in
place of interrupts.
</P
></DD
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