Micro Code

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

PCB Art

July 20, 2018 — Michael Engel

I just dug out an old Sparcstation 20 mainboard from my collection, since someone on Usenet was looking for a spare one to fix his broken machine.

Taking a closer look at the board, I found this little sketch of a bear with a top hat. I have worked with Sparc machines for more than 25 years now, but never noticed that little guy before. Neat!

Bear on board

Tags: sparc, sun, workstation, PCB art

More things from the dark corners of the lab cupboard

July 06, 2018 — Michael Engel

This is a MOS 6581 IC, the famous SID sound chip used in the Commodore 64 computer. Unfortunately, the "def." marking seems to indicate that it is defective. I'll have to test this...

MOS 6581 SID chip

Tags: MOS, 6581, SID, Commodore, C64, retrocomputing

Small is beautiful!

June 30, 2018 — Michael Engel

If you got into contact with computers in the 1980s (at least in Europe), there's a good chance that you have learned to program in Pascal, one of the languages designed by Prof. Niklaus Wirth at ETH Zürich.

Even though he is retired for several years now, to this day Prof. Wirth continues to design software and even hardware systems that follow the maxime "small is beautiful" - elegant and simple systems including more recent programming languages such as Modula-2 and Oberon, the whole Oberon system environment including a simple OS and a graphical user interface, and even complete computer systems. In-house designs at ETH were the early Lilith and Ceres workstations in the 1980s; more recently, Prof. Wirth designed a small RISC system on an FPGA including all peripherals that is able to run Oberon.

You can find more information on the Oberon system including all software and Verilog source code as well as a textbook describing the complete design at Project Oberon. Reading the sources is a nice project for a rainy weekend - the whole Oberon system's source code, including the compiler and GUI, is only about 10k LoC (written in Oberon, of course). The Verilog sources including the CPU, all peripheral interfaces and the video driver, amount to less than 1000 lines - impressive!

The Oberon FPGA system originally ran on a quite old FPGA board, the Xilinx Spartan 3 starter board, which features a Spartan 3S400, a tiny (by today's standards) FPGA, 1 MB of fast 32-bit SRAM, and a number of peripheral interfaces. I recently found my old Spartan 3 board and finally got the system to run.

Oberon on FPGA

In order to use the Oberon system, you have to connect a PS/2 keyboard and VGA monitor to the onboard ports. In addition, you need to connect an SD card (containing the Oberon file system image) and a PS/2 mouse.

For reference (you need to look it up in the ucf pinout definition file and figure out that SPI0 is the one the SD card is supposed to be connected to - SPI1 is reserved for some wireless network interface), here are the necessary connections to connector A2 on the board:

  • SD MISO: A2 pin 17
  • SD MOSI: A2 pin 7
  • SD SCLK: A2 pin 13
  • SD SSEL: A2 pin 5
  • SD Vcc (3.3V): A2 pin 3
  • PS/2 CLK: A2 pin 4
  • PS/2 DAT: A2 pin 6
  • PS/2 Vcc (5V): A2 pin 2
  • GND: A2 pin 1

I have used a generic Logitech PS/2 mouse (type M-BJ69) and a Waveshare Micro-SD adapter board with a SanDisk 8 GB card.

Tags: FPGA, Oberon, Xilinx, Wirth

It was twenty years ago tonight...

February 16, 2018 — Michael Engel

More looking through backups (what else would you want to do when it's -8 degrees outside?)... and another pictures folder, this time from 1998!

Back then, Linux was still a (rather) new and hot thing (and without systemd!). So, our Unix user group at Siegen Uni organised some events to gain more publicity for it. Our so-called "Linux Meetings" attracted up to 500 visitors over two days on a weekend.

So, here's a picture of yours truly from Linux Meeting 1998 in Siegen and some other impressions from twenty years ago... the shirt reads "Instant programmer... just add coffee", btw.

Me in 1998 Me in 1998 LM 1998 Big Tux LM 1998 plushies LM 1998 hackers LM 1998 impression LM 1998 sign

Tags: Unix-AG, Linux-Meeting, Siegen

Another blast from the past

January 21, 2018 — Michael Engel

While looking through some old backups, I came across a pictures folder dating from 2006. So, here's a picture of my office at TU Chemnitz, where I spent a year as acting professor for operating systems in 2006/07.

Nowadays, my colleague Matthias Werner occupies this office...

Chemnitz office

Tags: chemnitz, professor, office

Excursion Report Part 3: The Zuse Z23

January 01, 2018 — Michael Engel

The third part of our excursion to Erlangen was centered around the Zuse Z23 machine, which I already described in a previous blog entry about the Long Night of Science I attended some months ago.

Again, the demonstration of the machine was simply great - once more, thanks a lot to Volkmar and Edwin for hosting us!

So, here are some more impressions of the Z23 (original size photos available on request). All pictures are licensed under the Creative Commons CC BY-SA 4.0 license.

The machine and its operator

Z23 total

The computer itself

Z23 computer

Core memory modules

Z23 core memory

Hand-wired backplane

Z23 backplane

Close-up of some Z23 modules

Z23 module close-up

A page of the Z23 schematics

Z23 schematic

The magnetic drum unit

Z23 magnetic drum

Close-up of the drum read-write heads

Z23 drum heads

The magnetics of the drum itself

Z23 drum

Close-up of the head driver electronics

Z23 amplifiers

Tags: Zuse, Z23, FAU, RRZE, Erlangen, Excursion

Tiny Unix on a tiny microcontroller

January 01, 2018 — Michael Engel

There is one quite nice thing I (re)discovered over the Christmas break. At a MIPS FPGA workshop in Munich last January, I was given a ChipKit Wi-Fire board. This board is based on a Microchip PIC32MZ microcontroller, which includes a MIPS M14k CPU core with MMU and FPU, 2 MB of flash memory, 512 kB RAM and a number of peripherals.

This board is not only capable of running typical embedded operating systems, but is probably one of the tiniest platforms capable of running real Unix - namely the last BSD Unix version from UC Berkeley, 4.4BSD-Lite2. This final version from the CSRG research group came out in 1995 after a lengthy litigation in which AT&T (back then the owner of Unix copyrights) tried to hinder the publication of the BSD source code due to allegations of illegaly copied AT&T proprietary source code - luckily, this trial resulted in only six files which had to be removed from the BSD source code base; the 4.4BSD source code without the infringing files was then published as 4.4BSD-Lite2 and formed the basis for subsequent open source BSD projects, including 386BSD, FreeBSD, NetBSD, OpenBSD and DragonFly BSD.

Serge Vakulenko has worked on liteBSD, a port of 4.4BSD-Lite2 to the PIC32MZ MIPS-based microcontrollers for a number of years and managed to get it to work with the rather puny hardware resources of that controller (the MIPS architecture itself was supported by 4.4BSD in DECstation and SONY MIPS machines).

I got it to run on the Wi-Fire board (which is one of the boards supported out of the box by LiteBSD); it is quite an impressive achievement and, despite the minimal hardware resources, feels familiar to people used to modern Unix or Linux systems.

So far, I have fixed two bugs in the litebsd kernel source.

One was missing support for the execution of so-called shebang interpreted executables, i.e. shell scripts or similar (Perl, Python, awk, etc.), which start with the character sequence "#!" followed by the name of the interpreter, such as "#!/bin/sh".

The other was a bug in the memory allocation code for ktrace, which resulted in a kernel panic during execution tracing when tracing was enabled in the kernel.

There is also RetroBSD, an even smaller version of BSD for very tiny microcontrollers, derived from the last PDP11 BSD Unix version, 2.11BSD.

Some links:

Wi-Fire board litebsd screen shot

Tags: mips, pic32, BSD, unix, litebsd

Teaching Award

January 01, 2018 — Michael Engel

There are some things which I need to catch up on, since the last few weeks did not leave much time for blogging.

First, a very gratifying and unexpected event - I was awarded the University of Coburg Teaching Excellence Award for the academic year 2016/17 after only one year of teaching there. This was quite unexpected and I am very proud and happy to have received this appreciation of my work here.

The physical manifestation of the teaching award, as shown below, is a glass plate etched with a picture of Friedrich Streib, who was the founder of the predecessor institution of Coburg University in the 19th century. Quite nice and original!

Btw., this is my second teaching award. The first one was the so-called Lehrer-Lämpel-Pokel (Teacher Lämpel trophy, named after a character in the Max and Moritz illustrated verse stories by Wilhelm Busch) in the summer term 2015 at TU Dortmund, Department of Computer Science, for my course on computer architecture.

Teaching award

Tags: teaching, award, 2017