[Simh] PDP8, Adventure, and SIMH

[Rick Murphy]

At 01:16 PM 4/2/2013, Johnny Billquist wrote:
>On 2013-04-02 18:45, Rick Murphy wrote:
>>At 02:12 PM 3/29/2013, Rob Doyle wrote:
>>
>>>I just noticed that my PDP8 FPGA implementation differs from SIMH
>>>when dealing with mixed/lower case text.
>>>
>>>I also checked the operation on David Gesswein's online PDP8 and the
>>>operation of a real PDP8 matches the operation of my PDP8 FPGA and
>>>differs from SIMH.
>>>
>>>I did use exactly the same RK05 disk image for both SIMH and the PDP8
>>>FPGA. The image for the real PDP8 /could/ be different.
>>>
>>>I'm guessing that SIMH intentionally forces upper case because I didn't
>>>do anything special to the PDP8 FPGA. I didn't see any SIMH
>>>configuration options to change this.
>>>
>>>Is this intentional?
>>
>>The option you're looking for is
>>set tto 7b
>>
>>That will stop the case folding.
>
>I haven't looked, but I don't think that is the issue.

Well, since you haven't looked, I can tell you that I have tried it and 
that is the issue.

>The "old" ADVENT for OS/8 had the text in all uppercase in the database.

That's technically correct. That's technically correct all versions of 
OS/8 ADVENT, since FRTS on OS/8 only handles sixbit characters. 
However, the fact that the database is all upper case doesn't stop the 
program from outputting mixed case. I frankly don't remember if there 
was ever a public version of OS/8 ADVENT that only had upper case 
output, but I don't think there ever was.

What the original poster was seeing is that without "set tto 7b" all 
SIMH terminal output from the PDP-8 emulator is case-folded to upper 
case. What I provided is a way to see mixed case output.

This default case folding happens for any program running on the 
simulated '8 and can be demonstrated easily with other programs. For 
example, the built in DIRECTORY command summary line is output in mixed 
case, but without "set tto 7b" that line shows up in all upper case.

>  So, if you get lowercase output you have a different database than 
> the one I'm familiar with.

Well, I guess you know a lot more about OS/8 ADVENT than I do. Or 
you're playing an April Fools joke on me just a bit late. :) Hint, in 
case you haven't figured it out yet: *I* am the author of OS/8 Adventure.

>Also, ADVENT runs under the FORTRAN IV runtime system, which does not 
>use any OS/8 device drivers, thus any options set in OS/8 are unlikely 
>to have any effect.

You don't set any options in OS/8, you use the command above in the 
SIMH config file.
And no, FRTS does use OS/8 device drivers (which OS/8 calls device 
handlers). How else is a FORTRAN program going to read a disk file?

>FRTS is like its own operating system. It runs with interrupts, and do 
>most I/O on its own.

It does terminal I/O on it's own, yes. It also handles a few other 
devices internally (LPT, paper tape reader and punch), but relies upon 
OS/8 handlers for mass storage devices. Interrupts are disabled during 
OS/8 calls.

>It also have a FPP8 emulator, since most all code from FORTRAN IV is 
>actually FPP8 code, and not PDP8 code. This also means that things 
>runs way faster if you actually have a FPP8 in your machine.

You can also avoid the FRTS emulator if you use SIMH with the FPP8-A 
emulation code. That runs ADVENT now in FPP mode now that the fixes I 
submitted for the FPP emulator have been incorporated into SIMH V3.9.
         -Rick