Cromix Plus is a multiuser system, but to support more users requires more serial lines and terminals.
I had a Twin UART (TUART) card that would fit the bill and i’d purchased one more for another project, but it can be plugged into this rack for now. This would give a total of 5 users.
As for terminals – well they are hard to find so i have to be satisfied with a Windows machine with several serial ports and multiple instances of kermit.
The TUART is installed as TUART #1 as per the Cromix Plus Administrator’s Guide. This puts the ports at 20h and 50h and makes them 2 and 5 in the sysdefs file.
Cromix has been regenerated to enable the two TUART serial ports as devices tty2 and tty3. The disk controller serial port remains at tty1.
The TUARTs support interrupts, so the 16FDC no longer has the interrupt line to itself. Priority is established by a daisy chain that connects from the OUT on the 16FDC to the IN on the TUART. Just to mess with everyone’s heads, the IN and OUT positions on the TUART are the reverse of the 16FDC.
The serial ports can be configured as terminal ports by editing /etc/ttys:
Along the way, I stumbled on a Software Update Note for 20.14 that said:
This means that if no terminal is connected, the port should not be configured as a terminal port.
A second TUART was setup as TUART#2, but this clashed with the IDE card, so it was moved to TUART #3. These are 8 and 9 in the sysdefs file used to rebuild cromix.
The second TUART also needed to join the interrupt priority chain: OUT from the first TUART to IN on the second TUART.
Here’s an example of multiple users (3) and multiple processes (9):
(This pic is from after i increased the memory.)