Choice of Pi

[David Griffith]

I haven't yet acquired a Pi for my PiDP-8 or PiDP-11, so I'm wondering which one to get.  I'm inclined to get a Pi 3 because it doesn't require cooling.  Is there anything particularly desirable about using a Pi 4 for PDP emulation?

[Jeff Thieleke]

RPi 3b + Simh is about 6x as fast as a real 11/70.  Unless you want to multitask that RPi doing something else that needs the horsepower, I think 3b is the best choice.

[Steve Tockey]

The main advantage may simply be that the Pi 4 is noticeably faster than the Pi 3. FWIW, I am running Pi 3B+s on my PiDP-8/Is and PiDP-11/70. I throttle SIMH on the PiDP-8/Is run them at a historically-accurate speed. It's been my gut feeling (but without solid data to back it up) that even running PiDP-11/70 SIMH unthrottled on a Pi 3B+ is slower than a real 11/70. So maybe a Pi 4 could run closer to real 11/70 speeds?

I have also noticed that Raspbian has a serious time lag with the rest of the Linux world in terms of availability of other non PiDP related code like Docker and Eclipse. A Pi 4 can only run Raspbian Buster but Eclipse won't be available on Buster for quite a while. Docker may be available on Buster by now, I haven't checked. My point being that if you want to run other software like Docker (maybe) or Eclipse, you won't be able to do it (yet) on a Pi 4 and may have to use a Pi 3 where those things do run.

[Jeff Thieleke]

FWIW, I ran Dhrystone 1.1 both my 3b PiDP and "Miss Piggy" (https://www.livingcomputers.org/Computer-Collection/Vintage-Computers/Minicomputers/DEC-PDP-11-70-(-Miss-Piggy%E2%80%9D).aspx) as well as some of the benchmarks from https://archive.org/stream/byte-magazine-1984-08/1984_08_BYTE_09-08_Modula-2#page/n407/mode/2up and RPi3b and Simh is way faster in every benchmark.

[Steve Tockey]

Jeff,

Interesting, thanks. I appreciate the info.

[David Cornelson]

I was told by the guy at MicroCenter that the 3+ was better and getting a stronger power supply was key.

On Saturday, March 28, 2020 at 5:57:49 PM UTC-5, David Griffith wrote:

[David Cornelson]

Raspberry Pi 3 B+ with Inland 5.25V 2.4A Micro USB Wall Power Supply.

[Frank Laczko]

I am looking at the same question...any advantage to using a pi4?

I am using a 3A+ in the PIDP8I, but want to have Ethernet in the 11 that the 3A+ doesn't have. 

On Mon, Mar 30, 2020, 2:19 PM David Cornelson <david.c...@gmail.com> wrote:

Raspberry Pi 3 B+ with Inland 5.25V 2.4A Micro USB Wall Power Supply.

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[David Cornelson]

The 4 is the latest and greatest, but slightly pricier. For most tasks, the 3 B+ is probable more than enough.

On Monday, March 30, 2020 at 9:49:33 PM UTC-5, Frank Laczko wrote:

I am looking at the same question...any advantage to using a pi4?

I am using a 3A+ in the PIDP8I, but want to have Ethernet in the 11 that the 3A+ doesn't have. 

On Mon, Mar 30, 2020, 2:19 PM David Cornelson <david.c...@gmail.com> wrote:

Raspberry Pi 3 B+ with Inland 5.25V 2.4A Micro USB Wall Power Supply.

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[John Reinhardt]

On 3/30/2020 9:49 PM, Frank Laczko wrote:

I am looking at the same question...any advantage to using a pi4?

I am using a 3A+ in the PIDP8I, but want to have Ethernet in the 11 that the 3A+ doesn't have. 

A 3B+ will work just fine if all you want to run is the PiDP-11.  It has plenty of horsepower for that.  Going to e 3B+ gets you the wired Ethernet at 100Meg speed which is 10x (roughly) what the real PDP-11/70 could get on it's best days.

There is no real advantage to using a Pi 4B+ unless you plan to have some other things running in the background.  Perhaps using the HDMI for a Tek4014 graphics monitor or a GT40 graphics tube.

On Mon, Mar 30, 2020, 2:19 PM David Cornelson <david.c...@gmail.com> wrote:

Raspberry Pi 3 B+ with Inland 5.25V 2.4A Micro USB Wall Power Supply.

--

John H. Reinhardt

[Jonathan Morton]

> On 31 Mar, 2020, at 6:13 am, David Cornelson <david.c...@gmail.com> wrote:
>
> The 4 is the latest and greatest, but slightly pricier. For most tasks, the 3 B+ is probable more than enough.

The 1GB and 2GB RAM versions of the Pi 4 are $35, the same as a 3B+; only the 4GB version costs more.

You get more RAM (with the 2GB version), faster CPU cores, and *much* faster Ethernet, USB, and SD card access. The one downside is some extra heat, though that has been improved with updated versions of the firmware. I do suggest making sure the latest firmware is installed for that reason, but it will run safely without an extra heatsink.

The ports have changed a bit; power is supplied through USB-C instead of Micro-B, and there's two Mini-HDMI ports instead of one full-size one. I don't know precisely how that interacts with fitting cables into the PiDP chassis.

- Jonathan Morton

[Rene Richarz]

Yes, you get a more realistic emulation with tek4010 using a Pi4 with at least 2GB memory. I think the reasons are more graphics speed and more memory. This is especially true if you use tek4010 on the same Pi, attached to a high resolution display or VNC.

Best wishes to everybody in this difficult time.  Stay healthy!

[Heinz-Bernd Eggenstein]

(Replying to this old thread since it's still useful for newbies....)

When I tried to throttle simh on my Raspi 3B+ to roughly match a ca 1200 Dhrystone 1.1 score, I found the performance fluctuating quite a bit....and then I found out/remembered that the 3B has a somewhat special  thermal throttling enabled by default: max CPU clock is 1.4 GHz , but when the CPU temperature reaches a modest 60° C it already throttles down to 1.2 GHz . If it goes even higher (70 or 80° C??) it will throttle down aggressively  to prevent damage to the CPU, but that should never happen if you just run pidpd11-simh. So with a (say)  SET THROTTLE 1000k setting, my RasPi 3B+ was  alternating between  1.2 and 1.4 GHz depending also on ambient room temperature. which bugged me. So I installed a fan, because

• a PDP-11 schould make *some* noise after all, at least optionally when the significant other is not around :-)
  
• it keeps the CPU temp well below 45° C ==> constant performance of the PDP-11
  
• I think there kind of belongs a cut-out for a fan on the back next to all the serial connectors etc, plus some vents for the exiting airflow.
  

So as a general idea for a modest improvement of the kit, perhaps the backpanel could have a cut-out for an optional fan + vents. It would be cool if the fan would then blow down into a folded-cardboard "funnel" that could double as an insulation between the Pi and the frontpanel PCB and which would redirect the airflow 90 deg to blow into the space between the PI's and the PiDP'S  PCBs.....not sure if I made myself clear..... There is only a very modest airflow needed to keep the CPU below (for the raspi  3B+) 60°C.   

Best

HBE