Notes on libieee1284 on Windows NT/2k/XP

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The support for parallel ports in NT kernels is sub-optimal.  The port API

specifies capabilities such as ECP Hardware support, but ports that show up

as using the ECP driver don't actually return this capability.  Secondly,

data writes are not supported in non-ECP modes (ie, the only modes ever 

available).  To top it all off, control lines can be set to anything you want,

as long as it's the initialisation state.  We end up with essentially no way of

transferring data in through the parallel port.

To work around these problems there are two possible solutions:

1)  Use a driver such as PortTalk to give inb/outb permission to the 

    application (http://www.beyondlogic.org/porttalk/porttalk.htm)

    This appears an ideal solution, but requires the writing, compilation,

    and installation of a driver.  Compiling a driver requires the DDK, which

    is well beyond what most people have handy in NT.

2)  Reverse-engineer the (undocumented) ParallelVdm driver used by the 

    Virtual DOS Machine to provide printer compatibility.

    This option is suprisingly much simpler to implement, but has the 

    disadvantage that like the Solaris/x86 driver, every single read and write

    requires a syscall (and reads only transfer 4 bits in nibble mode), which 

    adds up to very slow operation indeed.

I opted for option number 2 as it took advantage of existing capabilities of

the OS.  Unfortunately this means amazingly slow operation, even on fast 

machines.  If you are keen to write a driver and installation routine for NT 

which does essentially what PortTalk does and doesn't require the DDK for 

compilation, please do!

Also note that F1284_EXCL is implicit in every use of the port in NT, as this

driver only provides one process with access at a time.

Enjoy,

- Matthew Duggan

stauff1@users.sourceforge.net