brainwagon

At the Maker Faire, I splurged for a little bit of computing hardware called the Beaglebone. It’s an $89 ARM based computer that runs at 700Mhz, and includes a MicroSD card slot and Ethernet, as well as a USB connector. I wasn’t sure what I was going to use it for, but I frankly can’t resist cheap hunks of hardware, and unlike the Raspberry Pi (which frankly is more interesting, since it includes video, which the Beaglebone lacks) you can actually walk up to a counter (well, at the Maker Faire you can) and buy one. So I did. Because Tom bought one. And I wouldn’t want to be left behind.

But what to do with it? Well, it boots Linux off the SD card, so I could do anything with it that I could do with a Linux machine. I’ve mused about my computing past before on this blog. So, I thought: “let’s see if I can get simh installed on it, and simulate the PDP-10/DEC 1091 of my computing past.

It’s frankly pretty trivial to do. It’s got gcc and wget installed, so all you have to do is fetch the source and compile it. You might want to get the pcap library installed so you can do simulated networking, and the machine itself is pretty slow (I discovered that when it’s powered from the USB, it runs at only 500Mhz, which seems really slow). But there is no trouble getting it installed. Then, all you need is some software to run on it.

In my previous excursion into the world of simh, I worked through installing TOPS-10 from scratch, but I didn’t feel like stumbling through that process again, so I searched the web and found a prebuilt image suitable for use. I downloaded it, unpacked it, and ran pdp10, starting it just as documented.

And… I was again hurled back through time. BASIC, COBOL and FORTRAN. 36 bit architecture. Craziness. Running on $89 worth of hardware, consuming 1W and the size of an Altoids tin.

I haven’t benchmarked it, but I suspect that it runs several times as fast as the original machine. I configured it to allow one to telnet into the server to simulate serial connections. I’m sure with a little work, I could dust off the corner of my brain that held information about this stuff, and figure out how to get ADVENTURE running.

And then I thought to myself: what if I wanted to hook real serial terminals to it? A little investigation reveals that the Beaglebone has six hardware UARTs. One is dedicated for connection via USB, but four are wired to expansion pins. I dug a little more, and uncovered this awesome project: the DECbox. The author mounted a beaglebone inside of a vintage DEC VT100. He even talks about modifying the VT100 to have serial connectors on the back so you can hook in additional terminals. Since the Beaglebone can simulate a wide variety of DEC machines, you could have a PDP-8, PDP-10 or PDP-11 all inside the same space.

Very cool. I’ll be keeping my eye out for a real VT100.

Addendum: in my spare time, I downloaded an image for the Gingerbread release of the Android OS. Because the Beaglebone doesn’t have a display, you start a VNC server which serves as a virtual graphics device, and then connect to it via a VNC client like TightVNC (for Windows) or Chicken of the VNC (for Mac OS X). I did this more for curiousity than anything else: it’s too slow to really be an adequate demo platform. But it might be of interest.

Addendum². I was digging around to find power requirements for the board. It turns out that if you don’t use the onboard USB, the current is supposed to be around 170ma, which makes the power less than 1W. But using the USB raises that a lot: the peak is almost 500ma during boot, which is about 2.5W. If you are concerned about power, ditch the USB as a power source.