Trying a new hack... and not understanding the instructions

[Paulo Rebordão]

I'm trying to add a 4-channel ADC converter (based on the ADS1115 chip) to my PiDP-11

by following the instructions on the "Hack" page but I encountered a snag:

At some point it says to copy files to /opt/pidp11/src/02.3_simh/src/PDP11 but my installation doesn't show the "src/PDP11" folder. Instead I only see the folder "4.x+realcons" inside "02.3_simh"

Am I missing something ?

[terri-...@glaver.org]

On Saturday, March 28, 2026 at 1:19:29 PM UTC-4 pjreb...@gmail.com wrote:

At some point it says to copy files to /opt/pidp11/src/02.3_simh/src/PDP11 but my installation doesn't show the "src/PDP11" folder. Instead I only see the folder "4.x+realcons" inside "02.3_simh"

Am I missing something ?

Oscar shuffled the layout a number of times, none of which I find particularly intuitive.

But I haven't changed it (yet) in my fork because it's what most people have installed

at present. If I do import a newer Open-SIMH that will all get cleaned up.

You probably want /opt/pidp11/src/02.3_simh/4.x+realcons/src/PDP11 

if you have a relatively recent installation. But there's no guarantee it will apply cleanly

on there, so keep a backup of your entire /opt/pidp11/src directory so you can re-

store if something goes "kaboom".

[Paulo Rebordão]

I have /opt/pidp11/src/02.3_simh/4.x+realcons/src/PDP11 

Bus as it was different from the instructions I wasn't sure if it was the right place 

Paulo Rebordão

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[Paulo Rebordão]

Ok. I copied the files to what should be the right place. Now I need to recompile Simh.

What's the correct way ? 

make -f makefile ?

Paulo Rebordão

A sábado, 28/03/2026, 20:51, terri-...@glaver.org <terri-...@glaver.org> escreveu:

On Saturday, March 28, 2026 at 1:19:29 PM UTC-4 pjreb...@gmail.com wrote:

At some point it says to copy files to /opt/pidp11/src/02.3_simh/src/PDP11 but my installation doesn't show the "src/PDP11" folder. Instead I only see the folder "4.x+realcons" inside "02.3_simh"

Am I missing something ?

Oscar shuffled the layout a number of times, none of which I find particularly intuitive.

But I haven't changed it (yet) in my fork because it's what most people have installed

at present. If I do import a newer Open-SIMH that will all get cleaned up.

You probably want /opt/pidp11/src/02.3_simh/4.x+realcons/src/PDP11

I have

if you have a relatively recent installation. But there's no guarantee it will apply cleanly

on there, so keep a backup of your entire /opt/pidp11/src directory so you can re-

store if something goes "kaboom".

--

[terri-...@glaver.org]

On Saturday, March 28, 2026 at 8:28:50 PM UTC-4 pjreb...@gmail.com wrote:

Ok. I copied the files to what should be the right place. Now I need to recompile Simh.

What's the correct way ? 

make -f makefile ?

cd /opt/pidp11/src; ./makeclient.sh

 

[Paulo Rebordão]

Tried something different.

Repeated the steps from the Obsolescence instructions:

cd /opt
sudo git clone https://github.com/obsolescence/pidp11
/opt/pidp11/install/install.sh

But this time, I asked to recompile the sources and got errors when recompiling Simh. The errors were coming from pdp11_sys.c and pdp11_io_lib.c

So the server failed the recompile.

I think it means the sources are inconsistent ?

Paulo Rebordão

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[Paulo Rebordão]

I managed to successfully compile simh, or rather realcons. 

The issue was that the obsolescence instructions for the bmp180 hack contain a few errors :

- the _sys and _io_sys files pointed by the link aren't the correct version for the rest of the source files. So I manually updated the existing files following the instructions on the hack page and eventually compiled without errors. 

- then I got into another issue: for the _io_sys file the instructions say to copy the entries for the PTP and PTR, rename them to ICP and ICR and just give them new addresses. But that's not enough - if the interrupt vectors aren't updated to different ones they clash with the vectors for PTP and PTR and simh fails when starting. 

This is an issue above my pay grade as I have no idea what interrupt vectors to allocate to the new devices ICP and ICR. 

Anyone can help? 

Paulo Rebordão

[Paulo Rebordão]

Ok, I'll give up for now.

I tried to adapt the hacking instructions for my device - a ADS1115 converter - but without sucess.

Using the i2c tools I can access it from the Debian prompt, read and write works fine.

But at the Simh level is not working. Apparently the read request is not reaching the pdp11_i2c.c code. Something is broken above it.

[Johnny Billquist]

Hmm. Not sure I understand. How do you access it "at the simh level"?
Did you add new commands to access that device, did you implement a
device at the simh level that you then expect to access from the PDP-11
side, in which case, what does it look like to the PDP-11? What CSRs are
you using, and so on... And if it's an A/D converter, maybe you should
create a device that looks the same as some existing A/D converter DEC
did, so that there already exist some software on the PDP-11 side to
make use of it, or else you'll need to write your own PDP-11 device
driver as well...

Johnny

> sudo git clone https://github.com/obsolescence/pidp11 <https://
> github.com/obsolescence/pidp11>

> /opt/pidp11/install/install.sh
>
> But this time, I asked to recompile the sources and got errors
> when recompiling Simh. The errors were coming from pdp11_sys.c
> and pdp11_io_lib.c
> So the server failed the recompile.
>
> I think it means the sources are inconsistent ?
>
>
> Paulo Rebordão
>
>
>
> On Sun, Mar 29, 2026 at 12:32 AM terri-...@glaver.org
> <terri-...@glaver.org> wrote:
>
> On Saturday, March 28, 2026 at 8:28:50 PM UTC-4
> pjreb...@gmail.com wrote:
>
> Ok. I copied the files to what should be the right
> place. Now I need to recompile Simh.
> What's the correct way ?
> make -f makefile ?
>
>
> cd /opt/pidp11/src; ./makeclient.sh
>
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[Paulo Rebordão]

It's working now.

What was wrong was really the address and then I forgot to remove some debug statements.

Anyway, here is what I think is wrong in the instructions:

- Inside Simh, for testing the new device, address should be 17776100 / 17776102 instead of 177716100...

- Copying the paper punch driver as the template for the new one will only work if you find new suitable interrupt vectors. Using the paper punch ones obviously won't work unless you disable (comment) them. I did that because I don't plan on using them.

Next step is to review the instructions for building an RSX device driver.

Paulo Rebordão

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[Lawrence Fisher (RealTimeCat)]

Paulo,

What you should be attempting to do is to take the SIMH module you have created from the papertape driver and create the PDP-11 registers to mimic one of the classic PDP-11 D/A devices such as the  AA11K or AM11K (see https://www.bitsavers.org/pdf/dec/handbooks/EB-20443-20_Peripherals_Handbook_1981.pdf for details). There are functional RSX-11 device drivers for those devices, as well as software that would make use of it without modification (you would still have to sysgen in the new devices into the RSX11 Monitor). These devices have also been utilized in RT11 software.

The SIMH module would provide the middle-ware to convert the Unibus register read/writes over to the appropriate I2C commands for your  ADS1115.  It would also be responsible for converting the 16bit analogue readings to/from the 12bit version that is used by the AA11K and AM11K.

I would like to look at similar capabilities for a 16 bit parallel DMA interface known as the DR11W, but I currently don't have the cycles to invest in that project today.

Lawrence Fisher

[Lawrence Fisher (RealTimeCat)]

Correction, the to A/D converts are the AA11-K and the AD11-K