Beyond the 128 device limit under QNX4.2x

---

Title: Beyond the 128 device limit under QNX4.2x
Keywords: nt960 Dev QNX4 QNX4.22 devices QNX4.23
Date: Feb 12 1997
Author: KAM
KDB Number: kdb-154
Distribution: External.


The QNX4 device manager "Dev" has the limitation of only being able to
administer up to 128 devices, this includes consoles, parallel ports,
serial ports and the null device. This means that there is usually only about
112 remaining unused devices. By default Dev is configured for up to 64 devices
this can be changed with the -n switch, Example:

Dev -n 128

So for customers wanting to use more than 128 devices it is necessary to run
more than one device administrator. To do this we must use the -N switch in combination
with the -n switch. We will also use the -N switch on Dev.nt960, to inform
Dev.nt960 of which device administrator to register itself with. See the
example below.

For example, we want to have a system running two host adapters with 80 ports
each. The total number of devices will be about 177, when we add up the number
of nt960 ports plus the other devices like consoles and so on. To accomplish this
you would need to configure the system like this....

Dev -n 96 &
Dev -N /dev1 -n 81 &
Dev.nt960 -a d0000 300,10 &
Dev.nt960 -a d2000 310,11 -N /dev1/nt -y cti/nt &

Dev:
-n is the number of devices to create.
-N is the new "Dev" directory name to register.

Dev.nt960:
-y This is used to change Dev.nt960's default registered name
to something other than cti/Dev.nt960. Use the QNX4 sin name to see the
registered names of programs that are currently running.
-N This is used to tell Dev.nt960 where to create the devices and what to
name them. This defaults to /dev/nt*.

Notice how the first Dev has 96 devices, this is ensure we have enough spare
devices to create all 80 nt960 ports, some consoles, a parallel port and the
null device. Since the second device is exclusively for NT960 ports we only
need 81 devices, that's for 80 nt960 ports and the null device. The null
device is created automatically.

The serial port names are created as:

/dev/nt1
/dev/nt2
.
.
.
/dev/nt80

/dev1/nt1
/dev1/nt2
.
.
.
/dev1/nt80

This allows users to create large systems with a large numbers of
ports (devices), possibly hundreds and not be hampered by the limitations of
Dev and QNX4.2x.