Title: Beyond the 128 Device Limit Under QNX4.2x
Keywords: nt960 Dev QNX4 QNX4.22 devices QNX4.23
Date: February 12, 1997
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
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 &
- n is the number of devices to create.
- N is the new “Dev” directory name to register.
- 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:
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.
End of KDB-154