Micro Code

Michael's blog about teaching, hardware, software and the things in between

Smalltalk on a small computer

June 12, 2020 — Michael Engel

In my previous post, I mentioned the Smalltalk system developed at Xerox' PARC research center starting in the early 1970s.

Smalltalk is a system that pioneered one of the first object-oriented languages (Objective C by NeXT/Apple inherited Smalltalk's ideas of object orientation and using messages to communicate between objects) and also one of the first graphical user interfaces, starting with the highly influential Xerox Alto computer system. In addition, Smalltalk programs are compiled to virtual machine bytecodes, which are in turn interpreted or JIT translated by the VM system (you didn't think Java invented this, did you?).

I was recently exchanging emails with Michael Haupt, an old friend of mine since our time as students in Siegen. Michael mentioned that my work on getting students interested in Plan 9, Inferno and Oberon was incomplete without also taking a closer look at the Smalltalk system. Specifically, the Smalltalk-80 system, which has excellent documentation in a series of books (collected by Stéphane Ducasse, thanks a lot!) which nowadays are freely available. The Blue Book (Smalltalk-80: The Language and its Implementation by Adele Goldberg and David Robson) is especially relevant, since it describes the details of the VM operating and bytecodes.

Of course, Michael was completely right!

By coincidence, Dan Banay had published a version of the Smalltalk-80 VM implemented in C++ from information in the Blue Book a couple of days prior. His version of the VM uses SDL for graphical output and input management and usually runs on several different Unix systems as well as Windows.

So I thought that might be an interesting project for a rainy weekend to look at. But, of course, simply compiling and running the system on a Unix host is boring, so what else could I do?

Some of my students will be working on porting Plan 9, Inferno and Oberon to RISC V systems. That was a bit too much for one weekend, so I looked for a challenge which was a bit less complex. I was already playing around with Plan 9 and Inferno on several Raspberry Pis here, so running Smalltalk bare-metal (without a supporting operating system) sounded like a nice challenge.

I got lucky and found a bare-metal environment that supported SDL running on the Raspberry Pi GPU and also USB input devices using the uspi Library. The most recent commit to the bare metal environment has been six years ago, so the platform it supports is the original Raspberry Pi (model 1B) - more recent Raspberry models have quite different processor cores. Luckily, the popular Raspberry Pi Zero models use the same system-on-chip (an ARM11 based Broadcom BCM2835) as the original Raspberry Pi, so these are supported by the library, too.

So I did not have to write too much code here - I combined the bare metal environment with the Smalltalk implementation and... nothing worked. Of course. A number of problems were still to solve:

  • Debug output was definitely required. I didn't have a JTAG interface set up on the Raspberry (it would be so nice if Raspberrys included a standard JTAG connector...), so I had to set up good old printf-style debugging on the Raspberry's serial interface.
  • The Smalltalk snapshot image (Smalltalk uses a persistent memory image, you don't have to boot the system from scratch every time you power up the system) could not be loaded, as there was no FAT filesystem support in the Smalltalk VM implementation (it usually uses standard POSIX calls). So I had to adapt the Smalltalk VM file system interface to use the FatFs module by Chan which is included in the bare metal environment.
  • Of course, this would have caused (and did...) lots of frustration right at the start of the project, so I employed a trick and converted the Smalltalk snapshot file to a nice, large C header file which was compiled with the VM program. Of course, this required changing all routines to access the image. But this worked well (Hint: xxd --include is really useful for this!).
  • The Raspberry Pi Zero has only one (OTG) USB port. Smalltalk, of course, needs a keyboard and a mouse, so my options were to either use a USB hub or a combined USB transceiver for a wireless keyboard/mouse set. Unfortunately, the ancient version of the uspi library only recognized one device on the wireless transceiver and none connected to the hub. So I spent more than a day integrating the most recent version of uspi. This one detects keyboard and mouse nicely but I was unable to get any data from the devices. After about a day of bug hunting I found out that I had inserted a debug printf in one of the interrupt handlers. Bad idea... the UART runs at 115200 bps, so outputting a 20 character string already takes about 2 milliseconds. No wonder that this completely messes up interrupt handling. Ouch. Now keyboard and mouse work nicely.

So I was able to stand on the proverbial shoulders of giants and add my little bit of hacking to it. But it runs, as you can see in this video and in the picture below.

However, there are still some problems:

  • The system hangs when switching to a different file in the editor without saving ("accepting") the changes to the current file first. A yes/no requester comes up (implemented as a BinaryChoiceView in the Smalltalk system), the cursor changes to a nice "thumbs up/down" cursor (long before facebook...) and after moving the mouse a bit the buttons are inverted and the system no longer accepts mouse clicks (as shown in the picture below). However, the mouse still moves and the VM is executing instructions. I am currently reading the Smalltalk-80 sources to figure out what is happening there.
  • The current version only runs on systems using the original ARM11-based BCM2835 SoC, but not the more recent multicore Cortex-A based SoCs in the Raspberry Pi 2/3/4. So the only supported Raspberry Pi versions are the original Raspberry Pi 1B (thanks for borrowing me yours, Joseph!), the Raspberry Pi Zero and the Zero W (with WLAN and Bluetooth, which are both unsupported in Smalltalk as of now). All these systems have been tested. It should also work on the original Raspberry Pi Compute Module (CM1), but I don't have one to test it on. Porting to more recent Raspberrys will at least require new startup code and probably new code for interfacing with the GPU.
  • The system is quite slow and takes about 20 seconds to boot. This is probably caused by the fact that the VM does a separate seek and read for every object of four bytes or so. Here, caching should obviously help.
  • Drawing the GUI is also slow, I will need to take a closer look at the bitblit routines and the SDL implementation. In the long run, getting rid of SDL and running directly on the framebuffer is an interesting option.

So, this is all a wild hack right now and the source code definitely needs some cleanup and tuning in addition to fixing the bugs. But it definitely was a very fun project already and it's great to have a system which enables the user to read the code and understand what's happening under the hood!

Of course, it will also serve as a nice basis for upcoming student projects, e.g. to implement a JIT, to work on multiprocessor support and to port to a completely open source (hard- and software) RISC V-based FPGA system.

So, stay tuned for updates and the publication of the code on github... this will take a bit, since the weather here in Trondheim is really nice right now...

Smalltalk on Raspi Zero W screenshot

Summer in Trondheim

Tags: Smalltalk, Raspberry, bare-metal

What have I been up to?

June 12, 2020 — Michael Engel

No blog updates for almost half a year - so at least a summary of what I did since January is in order.

Thinking about all the changes since mid March due to Corona, I get the impression that I spent most of my time here in Trondheim installing countless different videoconferencing and communication tools (Zoom, Teams, Slack, ...) and using them for so many virtual meetings. But, luckily, that's not all.

In fact, I have been busy creating a new version of NTNU's compiler course, since March also in the form of youtube videos. The semester here in Trondheim is over (and "spring semester" definitely was a misnomer this year, we had new snow until mid May here in Trondheim) and there is time to prepare for student projects.

I am happy to have found five highly motivated master students to work on interesting topics on the intersection of system software and compilers/programming languages. Some of the students will be working on the Plan 9 and Inferno operating systems from Bell Labs as well as Project Oberon by Niklaus Wirth.

Amazingly, all these projects share common ideas. Plan 9 was the successor of research Unix (8th to 10th editions) at Bell Labs, developed initially by the experienced Unix creators (Rob Pike, Ken Thompson, Dave Presotto and Phil Winterbottom). It is especially interesting since it tries to get rid of all the cruft that has accumulated in commercial (and open source - looking at you, Linux!) Unix variants and to build an OS that makes it easy to build distributed systems in a highly networked environment. Inferno is a project inspired by and forked from Plan 9 (around version 2, I think) which replaces native user-mode software by code executed in a virtual machine environment. The success of Java (which is itself already 25 years old now, yikes) seems to have had an influence here, too...

Oberon is the successor of Niklaus Wirth's Pascal and Modula-2 languages. Wirth started to build his own hardware and create the required system software at ETHZ to support his research and teaching. Oberon is the culmination of these projects; with Project Oberon Wirth also designed his own hardware description language (Lola) and RISC CPU (confusingly called RISC5 as the sixth in a series of iteratively more complex RISC designs - but Wirth was first) to run the Oberon language, operating system and integrated user interface. Readers of my blog might remember my previous experiments to run Project Oberon on an FPGA.

How does all of this fit together now? The relation between Plan 9 and Inferno (which is now commercially supported by VitaNuova systems in York, UK) is obvious. But there is more to it, which you can see if you compare a screenshot of Project Oberon and Rob Pike's integrated Acme development system for Plan 9. In his paper, Rob mentions a lineage of influences between different system. All starts with the Cedar system at Xerox PARC, where Wirth spent sabbaticals in 1976/77 and 1984/85 (according to Wikipedia), which was a major inspiration for Oberon. Acme, in turn, tries to apply some of the Oberon ideas to a development system for Plan 9 and, in turn, Inferno with its own Limbo programming language as well as the predecessor Alef on Plan 9.

So we're talking ancient unsupported operating systems here, right? Not quite... some of the Unix developers (Rob Pike and Ken Thompson) now work at Google on the Go programming language. The third person in the Go design team is Robert Griesemer, who was a PhD student at ETH Zürich with Niklaus Wirth and Hanspeter Mössenböck. Small world, isn't it?

I already mentioned Xerox PARC (Palo Alto Research Center). One of the interesting projects developed at PARC was the Smalltalk system developed by Alan Kay, Dan Ingalls, Adele Goldberg and many more talented researchers. Do you remember that Wirth spent some time at Xerox? So Smalltalk is the system missing in the overview here. It's very interesting in itself and the topic of a future blog post.

Tags: Trondheim, NTNU, Update, Plan9, Inferno, Oberon, Smalltalk



Picture credits: Oberon - SomPost (license BSDU), Acme - unknown, LPL license

Old VAXen never die...

January 05, 2020 — Michael Engel

...they just move North (shamelessly stolen from the NetBSD/VAX web page).

No, I didn't take an actual VAX up North (my two VAXen are currently in storage in Germany), but a large suitcase full of other electronic parts went with me to Trondheim, Norway in early December. As expected, this resulted in a special luggage exemination at Nuremberg airport. Luckily, the customs officers didn't require an explanation of every single of the many PCBs...

So, as some of my readers already know, I have decided to end my commitment with Coburg University at the end of 2019 in order to accept a position as associate professor for compiler design at NTNU in Trondheim.

NTNU letters

Arriving at the airport in Værnes, I was greeted with the appropriate weather:

Snow at Værnes airport

Luckily, I got an upgrade to my rental car from a puny Polo to a nice Mercedes GLC. This helped quite a bit, considering the road conditions:

Trondheim street] airport

So, last week I started my new job at the institutt for datateknologi og informatikk (Department of Computer Science). Stay tuned for more!

IDI sign]

Tags: NTNU, Trondheim, moving, snow, IDI

A Glimpse of Things to Come

November 19, 2019 — Michael Engel

Stay tuned for some big changes ahead... see the teaser picture ;-).

The times they are a-changing

Tags: teaser

Further back in time!

November 17, 2019 — Michael Engel

Back in the 1990s, some lecture notes were still handwritten. I just rediscovered these in the last folder hiding in a bottom corner of a bookshelf...

This is an excerpt from Wolfgang Merzenich's Programming Languages and Compilers course at Siegen Uni which I attended ca. 1995. 230 very well legible handwritten pages... great! Sadly, Wolfgang passed away far too early several years ago.

PuC lecture notes

Tags: compilers, course, merzenich, siegen

Blast from the Past part 2!

November 17, 2019 — Michael Engel

This piece is a bit more rare than the iPhone 2G and about two years older than the iPhone.

Before Nokia was destroyed by the hostile Microsoft takeover in 2013, they developed innovative early Linux-based mobile devices. The Maemo OS developed by Nokia is based on Debian, GNOME and a number of additional open source components. The Nokia 770 was the first commercially available system in this tablet series, followup devices included the Nokia 800 and 810. This was also the basis for Nokia's Linux-based mobile phones (N900 and N9, more on these in a later post).

This device runs on a 252 MHZ TI OMAP1710 SoC (ARM926EJ-S+C55x DSP) with 64 MB RAM and 128 MB Flash. The 4.1 inch display has a resolution of 800x480 and is usually used in widescreen format. Note that the system has no mobile wireless connectivity, only 802.11 and Bluetooth.

The Linux-based system previously used by Nokia is still being developed by the Jolla guys as Sailfish. Unfortunately, they seem to have only rather moderate success.

Nokia 770

Tags: Nokia, 770, tablet, Maemo

YABftP! (Yet Another Blast from the Past)

November 17, 2019 — Michael Engel

While cleaning out my apartment in preparation for a move, I rediscovered many pieces of hardware I haven't seen for quite some time :-). This is the first piece, so stay tuned...

This first piece is an original iPhone (called 2G, since it ran on GPS (resp. GPRS/EDGE) instead of the strange US CDMA standard - no LTE, UMTS or 5G...). It was introduced in June 2007 and features an ARM1176JZF-S based single-core SoC (Samsung S5L8900, this is long before Apple starts to design their own ARM cores) running at 412 MHz. The 2G uses 128 MB RAM and 8 GB of flash, the 3.5 inch display has a resolution of 240x320 pixels . This iPhone is still running after 12 years and is amazingly useable with iOS 3.1.3 - Safari, Google Maps and email work, whereas iTunes and the youtube app fail to start.

Maybe the CPU core used in the 2G rings a bell. This is the same core as the one used in the BCM2835 SoC in the original Raspberry Pi and the current Raspberry Pi Zero (W). However, the 5€ Raspi Zero has four times as much RAM and the CPU is clocked 2.5x as fast as the iPhone... if we only had the source code for iOS, a port to the Raspi Zero would be a neat hack.

The brochure the iPhone is resting on is of course also interesting for computer history afficionados... the TI Explorer is one of the few commercial LISP machines, based on a NuBus chassis and the TI S1500 asymmetrical multiprocessor 680x0-based Unix systems.

iPhone 2G

Tags: iPhone, 2G, ARM11, TI, Explorer

Assembler in Latin...

July 16, 2019 — Michael Engel

One of the obscure old computers you have probably never seen is the German Telefunken TR440, a 48 bit machine that came to market in 1970 and was intended to be a competitor for IBM's 360 and 370 series mainframes. Well, that didn't really work out...

While reading through the TR440's assembler manual (TR440 Instruction Set on bitsavers), I noticed that the mnemonics used were mostly abbreviations of German words (though I cannot figure out where "C" for store comes from).

If you look at the mnemonics used for Boolean operations, however, you start to wonder about their origin:

Boolean ops in the TR440

...that is, until you remember your high school Latin... et is probably pretty well-known and means and.

Then you figure out that this choice of mnemonics was pretty ingenious, since Latin -- in contrast to English or German -- has separate words for inclusive or (vel) and exclusive or (aut). Nifty!

Tags: Telefunken, TR440, assembler, latin, mnemonics