Signal generation on parallel port

I want to create square wave signal on parallel port with prorammable
frequency between 10-100Hz.

Can one of the Linux guru guide me what is the best way of generation of
squeare wave with highest possible frequency stability regardless of the
process load on the computer?

[Kasper Dupont]

Post by
I want to create square wave signal on parallel port with prorammable
frequency between 10-100Hz.
Can one of the Linux guru guide me what is the best way of generation of
squeare wave with highest possible frequency stability regardless of the
process load on the computer?

AFAIK the parallel port is not really designed for this kind
of signal. But of course it might still be possible. Changing
a line on the parallel port is so simple, that doing it from
an interrupt handler would be an acceptable solution. Depending
on the lack you can allow, it might be the only solution.

Before messing with kernel code, you should however try a user
mode implementation. Create a small program that will lock all
its pages in memory and use nanosleep in a loop. Before each
nanosleep call use gettimeofday to find out how long you need
to sleep. Alternatively you could use the tsc instead of
gettimeofday, on a single CPU system the tsc should be
perfectly accurate, some people have reported that gettimeofday
occationally acts weird.

When you program is working, and does not do anything horrible
like using all the CPU time, you can add a call to switch to a
real time scheduling class. That should give you the best
possible timing that can be achieved in user mode.

[Norm Dresner]

Post by
I want to create square wave signal on parallel port with prorammable
frequency between 10-100Hz.
Can one of the Linux guru guide me what is the best way of generation of
squeare wave with highest possible frequency stability regardless of the
process load on the computer?

You might look into Real-Time Linux.
http://www.fsmlabs.com/

If you hack around that site carefully, you'll find that there is a GNU
(free) version of RTLinux that is quite capable of creating heavy-duty,
industrial-strength applications. We've used it for almost 8 years to do
testing of avionics and find that we can trigger a periodic task with only a
few microseconds of jitter.

Norm

[Rich Walker]

Post by Norm Dresner

Post by
I want to create square wave signal on parallel port with prorammable
frequency between 10-100Hz.
Can one of the Linux guru guide me what is the best way of generation of
squeare wave with highest possible frequency stability regardless of the
process load on the computer?

You might look into Real-Time Linux.

Alternatively, look at www.rtai.org.

RTAI will (just about) let you do this from user space.

It's a really nice piece of kit.

cheers, Rich.

[7]

Post by
I want to create square wave signal on parallel port with prorammable
frequency between 10-100Hz.
Can one of the Linux guru guide me what is the best way of generation of
squeare wave with highest possible frequency stability regardless of the
process load on the computer?

Try this site http://parapin.sourceforge.net/

[MS. Mo]

On Fri, 19 Nov 2004 22:45:25 +1100

I want to create square wave signal on parallel port with programmable
frequency between 10-100Hz.

Few times ago, I had to write a software that does control an old adc, connected to an old SPP parallel port.
I did'nt had to use EPP/ECP so I dunno if it works too, but you can check that by yourself with an oscillo :)


The || port is composed of 25 pins, and part of those pins can be controled separately by
throwing bits in the parallel port registers.

in outgoing way,

1 mean +5V
0 0V

first here's the pin assignation:

Pin No (D-Type 25) SPP Signal Direction In/out Register

1 nStrobe In/Out Control
2 Data 0 OUT Data
3 Data 1 OUT Data
4 Data 2 OUT Data
5 Data 3 OUT Data
6 Data 4 OUT Data
7 Data 5 OUT Data
8 Data 6 OUT Data
9 Data 7 OUT Data
10 nACK IN Status
11 BUSY IN Status
12 PaperO/E IN Status
13 Select IN Status
14 nAutoLF IN/out Control
15 nError/nFault IN Status
16 Initialize IN/out Control
17 nSelect Printer/ nSelectin IN/out Control
18-25 ground gnd

then to access the parallel port you'll have to use a special adress called the BASE adress
usually located @ 378h.
To create a square wave, on a certain pin, all you have to do is writing a 1 at the
corresponding bit in the right register. The correspondance bit <-> pin is shown below

in BASE+0 (Data register)
you can control all the data bits, bit 0 <--> Data 0 and so on
their main purpose is to send information to a peripherial device so you might use those
to generate your wave.

in BASE+1 (status register)
Bit 7 Busy
Bit 6 Ack
Bit 5 Paper Out
bit 4 Select
bit 3 Error
bit 2 IRQ (tell the system to use IRQ or not)
bit 1 and 0 are reserved (?)
and the last
BASE+2 (Control port)
bit 7 and 6 are unused
bit 5 enable bidirectionnal mode
bit 4 enable irq via ack line
bit 3 select printer
bit 2 init printer
bit 1 auto linefeed
bit 0 strobe

so now you have all the register <-> physical pin association
The registers are used via 2 kernel functions, inb (read the register) and outb (write on it)
those are fast but require to run as root (other people use read/write on /dev/lp)
and require also to use ioperm to tell the kernel to allow the application to access the port.

here's an example:

#define BASE 0x378 /* || port base adress */

then use ioperm to grant the permissions:

int ioperm(unsigned long from, unsigned long num, int turn_on);

in your case you'll only use the base address
if(ioperm(BASE,1,1)) {perror("Ioperm b0rked"); exit (0);}

and then you can use
outb function to create your square with a loop
it might look like this:

char byte = 0;
int i;
for(i = 0; i < 1000; i++){
outb(byte,BASE);
byte ~=byte; /* alternate 0 - 1 */
usleep(10000); /* use this for the frequency adjustments */
}

the time specified for usleep is in microseconds.

You might also have a look at beyond logic
http://www.beyondlogic.org/spp/parallel.htm

Can one of the Linux guru guide me what is the best way of generation of
squeare wave with highest possible frequency stability regardless of the
process load on the computer?

Dunno if I'm clear, but
I hope it helps :)

Mo