Re: Re: Is xPL the ideal work-around? Need to access the LPT port from Mister House...

[Gerry Duprey <gerry@xxxxxxxxxxx>]

Howdy,

In the hopes of being able to use this cross platform, here are a couple of
thoughts:

> Bytes would be written using an xpl-cmnd message like:
>
> Control.basic
> {
> Device=888 (decimal address of LPT1)

The 888 part seems a bit problematic to me.  For one, it's really, really
platform specific (to the point that two different machines on the same O/S
may not have things at the same address (you can put devices at other
addresses or have "virtual" device, etc)).

Here's a couple of thoughts:

1) Use device names (LPT1, /dev/lp0, etc)
Better abstracts things, allows the actual physical device to be resolved
on
the target machine, though still does not provide a uniform xPL level
naming
scheme

2) Use device= and unit= (device=Parallel, unit=0 == LPT1 or /dev/lp0)
Breaks things up into the general class of I/O and the unit within in. 
That
is likely to be pretty easy to interface with via xPL from other platforms.
Of course, the unit= thing breaks control.basic

3) Use a extension of control.basic: control.parallel and control.serial

control.parallel
device=<unit # (0, 1, 2) or name (LPT1, LPT2, /dev/lp0)>
type=byte
current=255[,100[,200]]

The extra bytes on the current= allows simple multi-byte writes (optional
(that is what the [ and ] are meant to indicate) -- I could deal with one
byte per packet, though that could be a bit wasteful when doing lots of
control).  While I think it would be nice to also allow hex notation (i.e.
0xff), I'm ok with decimal only.

I think it would be good to also have a type=text and current= be an ASCII
string that is sent out character by character.  This would make things
like
LCD displays and such easier to work with (send a few control characters,
then a message to display)

control.serial
device=<unit # or name (COM1, COM2, /dev/ttyS0, etc)
type=byte
current=255[,100[,200]]
[config={3001200240048009600192003840057600etc]},{78},{EVENODDNONE},{CTSXONNONE}]

The optional config= tag would allow you to set the baud rate, data bits,
even/odd/none parity and CTS/XON/NONE handshake.  If omited the serial port
is used at it's last settings (i.e. nothing changes).  This could also be
broken down into a baud=, databits=, handshake= and parity= tags too --
perhaps that would be better?

I believe I can put together a Java x-platform version of this, but I do
know that it would not be able to do anything with a device address like
888
because it would be abstracted and inaccessible.

Gerry
--
Gerry Duprey
Ann Arbor, MI 48103
http://www.cdp1802.org