OIS 140 IPL description


The 140 contains three 2708 EPROMS with elaborate hardware diagnostic routines and a small bootstrap loader program. There is a different set of EPROMS for each of the fixed disk controller board sets. The programs in these perform the following functions:
Each of these tests is detailed on the front panel and CPU board LEDs. There is a reference here.

Once the tests pass (the disk tests are only run for the controller for the disk you set to IPL from), an attempt is made to load the second sector from the disk into memory at location 1000h. This is checksummed, and if it passes, control is passed to this program.
The 'IPL sector' has the disk's address and geometry hard-coded into it. This is done when the operating system is installed. This program calls the routine in the EPROM to load the master code into memory. The location (sector number) and size (in pages) of the master are hard-coded into the IPL sector also. The master is loaded starting at address 1100h, and is EFh pages in length. (as of version 10.5). Once this is loaded, the IPL sector loads the disk's volume label (sector 0) into memory at 6d00h. It then passes control to the master at 6e00h.

The IPL code at 6e00h is responsible for allocating memory for the following:
The IPL code also determines which disk controller is in use. If the Winchester controller is in use, the code for the SMD controller is overwritten, as well as the SMD disk definition tables.
If the debugger is not in use, it is also overwritten.

(Note: if you're using the IDE disk, it doesn't care, it just goes ahead and uses the horrible code I hacked in to it.)

If you set up the Debug level 2, the process stops here. The workstation on port 1 will beep and you will see:

debug

You can use the debugger to poke around in the Master here. If you type 'G' and press Execute or Enter, the process continues.

Next, the system volume is mounted. If this succeeds, an overlay is loaded that will overwrite the IPL program. This overlay is hidden on the system disk (like the master) and can be found on the Starter diskette as SYSGEN.MASTER.OVERLAYS. It contains code for several of the OS-6 non-immediate requests.

Now, we can talk to slaves, so we don't need to use the LEDs for diagnostic messages anymore! (But the LED's are fun, you say. Okay, let's see you toggle bits in four bits at a time, using the diagnostic toggles and the DPB button...Don't ask..)

But, you don't want to see this:

RCB Error

The file DOS.IPL is loaded to any workstations. This is where you see the screen asking for the date and time (but don't enter 03 for the year - it doesn't like anything past 99!). When the date and time are set, the file DOS.START gets loaded. This determines the device type and loads the appropriate program:
(The screen images on this page are from the OIS Emulator.)

Back