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doc/other.xml: Add extra details about range and aref.

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Add extra detail to the section on acquisition functions about the
range and aref parameters, and describe the comedi_range type.

The whole section is still a bit higgledy-piggledy and could do with
some rearrangement one day!
This commit is contained in:
Ian Abbott 2012-05-09 18:41:51 +01:00
parent 98869fa36d
commit dbe3c77a3d
1 changed files with 54 additions and 2 deletions
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56
doc/other.xml
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@ -178,7 +178,32 @@ Single samples can be read from an analog channel using the function
</funcprototype></funcsynopsis>
This reads one such data value from a &comedi; channel, and puts it in
the user-specified <parameter>data</parameter> buffer.
the user-specified <parameter class="function">data</parameter> buffer.
</para>
<para>
The <parameter class="function">range</parameter> parameter is the zero-based
index of one of the gain ranges supported by the channel. This is a number
from 0 to N-1 where N is the number of ranges supported by the channel.
Use the function
<function><link linkend="func-ref-comedi-get-n-ranges">comedi_get_n_ranges</link></function>
to get the number of ranges supported by the channel, the function
<function><link linkend="func-ref-comedi-find-range">comedi_find_range</link></function>
to search for a suitable range, or the function
<function><link linkend="func-ref-comedi-get-range">comedi_get_range</link></function>
to get the details of a supported range.
</para>
<para>
The <parameter class="function">aref</parameter> parameter specifies an
analog reference to use:
<constant><link linkend="aref-ground">AREF_GROUND</link></constant>,
<constant><link linkend="aref-common">AREF_COMMON</link></constant>,
<constant><link linkend="aref-diff">AREF_DIFF</link></constant>, or
<constant><link linkend="aref-other">AREF_OTHER</link></constant>.
Use the function
<function><link linkend="func-ref-comedi-get-subdevice-flags">comedi_get_subdevice_flags</link></function>
to see which analog references are supported by the subdevice.
</para>
<para>
@ -231,7 +256,7 @@ and <function><link linkend="func-ref-comedi-from-phys">comedi_from_phys</link><
</para>
<para>
There are two data structures in these commands that are not fully
There are some data structures in these commands that are not fully
self-explanatory:
<itemizedlist>
@ -256,6 +281,33 @@ munging</quote>.
</para>
</listitem>
<listitem>
<para>
<type><link linkend="ref-type-comedi-range">comedi_range</link></type>:
this holds the minimum and maximum physical values for a gain range supported
by a channel of a subdevice, and specifies the units. This can be used in
combination with the channel's <quote>maxdata</quote> value to convert between
unsigned integer sample values (of type
<type><link linkend="ref-type-lsampl-t">lsampl_t</link></type> or
<type><link linkend="ref-type-sampl-t">sampl_t</link></type>) and physical
units in a nominal (uncalibrated) way using the
<function><link linkend="func-ref-comedi-to-phys">comedi_to_phys</link></function>
and
<function><link linkend="func-ref-comedi-from-phys">comedi_from_phys</link></function>
functions. Use the
<function><link linkend="func-ref-comedi-get-maxdata">comedi_get_maxdata</link></function>
function to get the <quote>maxdata</quote> value for the channel.
</para>
<para>
Most functions specify the range to be used for a channel by a zero-based
index into the list of ranges supported by the channel. Depending on the
device and subdevice, different channels on the subdevice may or may not
share the same list of ranges, that is, ranges may or may not be
channel-specific. (The <constant>SDF_RANGETYPE</constant> subdevice flag
indicates whether ranges are channel-specific.)
</para>
</listitem>
</itemizedlist>
</para>
<para>