Treating parallel port as serial device

Treating parallel port as serial device

[Tony Hoyle]

I'm looking to attach a serial device to my box that has only TTL level
I/O.  Since I'm more of a software than a hardware person making a
circuit board up with a max232 in is a bit risky...  I want to connect
the I/O to the parallel port.

What I need now is a driver that can read the input from a  pin on the
parallel port and treat it as serial input.  It sounds like the kind of
project that would have been done before, but I can't find anything that
even comes close.  Userspace probably wouldn't cut it as I'm reading as
9600 baud and usleep doesn't have nearly enough resolution.

Tony

-- 
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said their coffins preferred it.

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Re: Treating parallel port as serial device

[Philip Blundell]

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>even comes close.  Userspace probably wouldn't cut it as I'm reading as
>9600 baud and usleep doesn't have nearly enough resolution.

9600 baud is only 1 bit every 100us or so.  SCHED_FIFO and nanosleep should be 
perfectly adequate for timing.  You can use ppdev or direct port I/O to get at 
the pins.

p.


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Re: Treating parallel port as serial device

[Christopher Friesen]

Tony Hoyle wrote:

> What I need now is a driver that can read the input from a  pin on the
> parallel port and treat it as serial input.  It sounds like the kind of
> project that would have been done before, but I can't find anything that
> even comes close.  Userspace probably wouldn't cut it as I'm reading as
> 9600 baud and usleep doesn't have nearly enough resolution.

Unless you need to drive this based on interrupts or you need to do other stuff
at the same time, you can use either SCHED_FIFO or SCHED_RR and nanosleep() from
userspace.

According to the man page, nanosleep() will busywait for pauses under 2ms if you
use one of the two realtime schedulers.

Chris

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Re: Treating parallel port as serial device

[Jean-Christian de Rivaz]

Take a look to the MAX3100 chip:
http://pdfserv.maxim-ic.com/arpdf/MAX3100.pdf

This solution highly reduce the CPU overhead needed to sample Rx line 
for each single bit. The chip have a FIFO, an interrupt and look like a 
standard UART. Only the bus transfert with the CPU is different.

I curently work on a driver for it.

Regards,

Tony Hoyle wrote:
> I'm looking to attach a serial device to my box that has only TTL level
> I/O.  Since I'm more of a software than a hardware person making a
> circuit board up with a max232 in is a bit risky...  I want to connect
> the I/O to the parallel port.
> 
> What I need now is a driver that can read the input from a  pin on the
> parallel port and treat it as serial input.  It sounds like the kind of
> project that would have been done before, but I can't find anything that
> even comes close.  Userspace probably wouldn't cut it as I'm reading as
> 9600 baud and usleep doesn't have nearly enough resolution.
> 
> Tony
> 
> 

Re: Treating parallel port as serial device

[H. Peter Anvin]

Followup to:  <9mgtpb$mf4$1@sisko.my.home>
By author:    "Tony Hoyle" <tmh@nothing-on.tv>
In newsgroup: linux.dev.kernel
>
> I'm looking to attach a serial device to my box that has only TTL level
> I/O.  Since I'm more of a software than a hardware person making a
> circuit board up with a max232 in is a bit risky...  I want to connect
> the I/O to the parallel port.
> 

Most RS232 boards accept TTL level input, so your only problem is
output.  You may want to simply construct a level converter, such as a
voltage divider or zener diode on your input.

	-hpa
-- 
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"Unix gives you enough rope to shoot yourself in the foot."
http://www.zytor.com/~hpa/puzzle.txt	<amsp@zytor.com>