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>IEEE 1284 transfer modes</H1
><P
> Stacked on top of the sharing mechanism, but still in the
<TT
CLASS="LITERAL"
>parport</TT
> module, are functions for
transferring data. They are provided for the device drivers to
use, and are very much like library routines. Since these
transfer functions are provided by the generic
<TT
CLASS="LITERAL"
>parport</TT
> core they must use the <SPAN
CLASS="QUOTE"
>"lowest
common denominator"</SPAN
> set of access functions: they can set
the control lines, examine the status lines, and use the data
lines. With some parallel ports the data lines can only be set
and not examined, and with other ports accessing the data register
causes control line activity; with these types of situations, the
IEEE 1284 transfer functions make a best effort attempt to do the
right thing. In some cases, it is not physically possible to use
particular IEEE 1284 transfer modes.
</P
><P
> The low-level <TT
CLASS="LITERAL"
>parport</TT
> drivers also provide
IEEE 1284 transfer functions, as names in the access function
list. The low-level driver can just name the generic IEEE 1284
transfer functions for this. Some parallel ports can do IEEE 1284
transfers in hardware; for those ports, the low-level driver can
provide functions to utilise that feature.
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