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Booting a RT-11 on a PDP-11/73 using the RX50 drive

fabioNMI

fabioNMI

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Joined
Aug 26, 2024
Messages
39
Location
Ingersoll, Ontario, Canada
Hello!
I am totally new to PDPs and I just got my hands on a Micro PDP-11/73 with 4MB of RAM and RD53/RX50 drives. RD53 is DU0 and the system is unable to boot from there, the disk seems to be spinning but the error message says it is not ready.
I got some RX50 floppy disks here, some seem to have bootable RT-11 5.01, there is also RSX-11 3.0 and RSX-11 4.0 installation disks.
I am trying to boot via floppy drive using B DU1 (also tried B DU2 for the second half of the RX50).
When I try to boot the RT-11 disks, I get:
Starting system
on my VT101 and after a couple seconds I get the error message:
?BOOT-U-I/O error
000724
@
I know the "@" is the ODT prompt, but I could not determine why I get the error message. And more importantly: all RT-11 disks give me the same error at the same point!
So I decided to use my 386 with PUTR and it can mount and read the floppy disks, so I believe they should be good?
Just in case I decided to image the disks using IMD and create new copies on DSDD disks, I know that if there is an issue on the disks it will be propagated to the new copy but I just wanted to check whether I can properly image those disks with IMD or not. It seems that I can because PUTR could read the very same directory and files.
BUT when I try to boot RSX-11 v3.0, something else happens, the very first time I tried it, it booted up to a prompt! But every try after that resulted in a kind of loop, after the "Starting system" message the drive keeps cycling reading the disk forever and nothing else happens.
I thought it could be dirt on the drive so I disassembled the RX50 and cleaned it thoroughly (it was super dirty inside) and lubricated the rails, but nothing changed.
I have some many questions! But the main question is: does that sound like an RX50 drive problem? Is there something else I could try? I will try to get some extra RX50 drives for trying but I would appreciate if someone with more knowledge than I (mostly everybody else lol) could shed some light or give me some other ideas I could try.
Btw.: I tried VERY HARD to find RT-11 images for the RX50 but I could not find them anywhere, do they exist? Can someone point me to where I can get them?

Thanks in advance!
 
Try to boot the imaged disks on a SIMH image. They may not have a proper boot block.
 
Welcome to the world of PDP-11's...

Does your machine have the little front panel with the drive ready and write protect switches?

If so, these may be set incorrectly.

Dave
 
Write protect should illuminate RED if the disk is protected.

Ready should illuminate GREEN if the drive is ready.

The button is push on, push off.

HALT obviously returns the machine to ODT. I think this button illuminates RED when operated. Make sure you return it to normal after entering ODT.

Restart should reboot the CPU.

Dave
 
daver2 said:
Write protect should illuminate RED if the disk is protected.

Ready should illuminate GREEN if the drive is ready.

The button is push on, push off.

HALT obviously returns the machine to ODT. I think this button illuminates RED when operated. Make sure you return it to normal after entering ODT.

Restart should reboot the CPU.

Dave
Click to expand...
Thanks, yes they are all operating as expected. Write protect is not pressed (and not red), pressing it turns red so I know it works. Ready is green, the disk reads as I mentioned before, but gives me that BOOT-U-I/O error, I will try to get
 
I have just tried my disk image on SIMH, this is what I did:
1 - used IMDU /b to convert the IMD image to DSK
2 - Created a simple boot.ini as follows:
set cpu 11/73
set rx enabled
attach rx0 RT11.dsk
boot rx0
3 - Ran SIMH using the above boot.ini and this is what I got:
%SIM-INFO: RX0: buffering file in memory
Trap stack push abort, PC: 000014 (SUB #162745,-(R5))

That is not the same issue I see on the real PDP/11-73 so maybe the image is not good or the conversion with IMDU missed something
 
Next step is to check your work on SIIMH: Find a "good" boot floppy image and try to boot off that.

Once you get something that boots in SIMH then try to move it to a "real" RX50 and try "really" booting that.

Try to do things one small step at a time.
 
I have RT-11 booting on SIMH, but it is from a hard drive (RK07) and I did not manage to get RT-11 to format and initialize a virtual RX50 disk, after spending hours on SIMH and getting nowhere I decided that I felt I was making more progress on the actual PDP-11. But I can go back to SIMH...
 
Hm, that's weird. Remember after copying RT11FB and the DU driver to do a copy/boot:du du0:rt11fb.sys du0: or whatever drive number you have for your virtual floppy
 
Ok good news! Some progress with SIMH!!!
I decided to use PUTR to generate the dsk image using the COPY command:
copy /device /file b: RT11.dsk
And did some research and updated my boot.ini to:
set cpu 11/73
set rq0 rx50
attach rq0 RT11.DSK
boot rq0

And now SIMH boots to RT11!
%SIM-INFO: RQ0: 'RT11.DSK' Contains RT11 partitions
%SIM-INFO: 1 valid partition, Type: V05, Sectors On Disk: 800

RT-11SJ (S) V05.01B

.SET TT QUIET
?KMON-F-Invalid device LS:

.

So now I know that the floppy I have here works on SIMH but not on the real machine, what could be the issue?
 
I would try and run the MAINDEC diagnostics on your system.

Either try and boot XXDP from your floppy or use the paper tape versions of the individual diagnostics.

There is a PC utility that will transfer these files to a machine over the console serial port when the machine is sat in ODT (PDP11GUI).

Ah yes, the RX device is for an RX02 (for example) but the RX50 is a DU device - so your SIMH initialisation file was incompatible with your media bootstrap.

Dave
 
Can you try: "SH DEV:DU" on SIMH and post the output here please... The DU driver may not be configured correctly for DU2

Also, have you checked your DU controller CSR setting?

Robin
 
As you are realising, there are a lot of things that can go wrong with just booting a system!

Especially if you are taking an image off the web and just using it.

Dave
 
fabioNMI said:
?BOOT-U-I/O error
Click to expand...
This message is output by the RT-11 boot block, so at least the boot block was read without errors. Its routine then attempts to read some block but receives an error from the controller, which is what causes this message and HALT. If my memory serves me correctly, attempting to continue execution (of the P ODT commands) will result in another read attempt.
 
Yes - could be the controller is not at the expected address for the DU driver config on the disk - or the controller drive numbering (starting LUN) has been changed from 0...

Basically - set it to factory default settings!

Also - change the SIMH config to boot it from DU2 (RQ2) instead of DU0 and see if that works...

Robin
 
Typically, into the boot block code in R0 passes the device number, and in R1, the CSR address. However, the DU driver, at least since version 5.01, only uses the device number, with the CSR hardcoded into the primary boot block. Judging by the fact that simh is being loaded, it's likely using the standard address 172150.
 
Good morning all!
Thanks for all the replies here, yesterday night I learned a bit more:
1 - the original RX50 is an "A" revision, with a solenoid that lands the head on the disk for reading/writing
2 - I also got four extra RX50s but they are all in terrible shape, I noticed that they are all "B" revision and don't have the solenoid
3 - Played a lot with the original RX50-AA rev A and decided to try the rev "B", two of them have rusty rails so that was a no-go from the start, on all of them the spindle was not spinning. I completely disassembled the drive that looked less bad, lubricated the spindle ball bearings (both units) and cleaned/lubricated the rails. On that drive the RT-11 disk seems to go further, I don't get the error message but the head moves from track zero towards the the inner tracks for some time and after a couple seconds of reading it moves back to track 0 and the spindle keeps cycling on and off, left it for a couple minutes but it doesn't seem it is going anywhere. Tried multiple times and it is always the same behaviour. Bummer!
4 - Took the RSX 4.0 installation disk and tried it on the Rev B RX50 (same used on step 3 above) and guess what? It boots up! So know I know that the drive works and the controller works, but I don't understand why all the three different RT-11 boot disks I have here fail in the exact same way! Just to clarify none of them were imaged, they are all old (non-original) disks I got with the PDP. They all seem to be RT-11 v5.01
So where am I standing now:
A - the original RX50-AA rev "A" gives me the "?BOOT-U-I/O error" when I try my RT-11 floppies;
B - the original RX50-AA rev "A" enters an endless loop trying to boot RSX 4.0 installation disk;
C - the RX50-AA rev "B" enters an endless loop trying to boot my RT-11 floppies (but no "?BOOT-U-I/O error");
D - the RX50-AA rev "B" successfully boots the RSX 4.0 installation disk;

So at this point I can have the PDP-11 to boot to something, but it is not a usable OS (or is it? I don't know! Can I get to a CLI from that RSX installation disk?)
I still don't understand why all the old RT-11 disks fail in the exact same way!
 
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