Boards

For reasons mostly related to the pandemic, we did not attend VCFb since 2019. Finally, this year we managed to be there again, just im time to show our newly assembled rev0.6 (and fully working !!!) SBC boards around, and have tons of fun with other very nice people there (Hello https://mega65.org/!). Also, we talked about how the Steckschwein evolved over the last almost 10 years and about our development methodology. As always at VCFb, the talk was streamed and the video is available at media.ccc.de. Our slides from our talk can be downloaded in PDF format here and here.

After some troubleshooting, we finally finished Revision 0.6 of our boards, and the new boards are finally there, ready to be assembled. We managed to fix all the issues we found, and also did some cleaning up, used better footprints for the resistors and the mini DIN jacks.
Soldering session coming up..

Revision 0.6 boards are there

Our debugging journey at VCFe began right at powering up the board the first time, when something got real hot real fast. Fair enough, and easy to spot. There was a mixup of VCC and GND at U29, a 74HCT244. Embarassing, but not that critical, as U29 is only used to connect the joystick ports to Port A of the VIA. We can live without them for now.
The mixup likely happened when I transferred the IO-board schematics from KiCad 6 to 7 while updating the symbols from the current library, which happened to be different than the old ones. I had to mirror the new symbols to fit the schematic. This meant that GND is at the top now, and VCC at the bottom. Which I happened to overlook. While routing, I was briefly wondering why U29’s bypass capacitor was at the opposite corner compared to all the other 74HCTnnn chips. I maybe should have become suspicious at that point.

Our plan for VCF2 22.0 was to assemble the first Steckschwein SBC right at our booth as some kind of show-cooking event. That only half worked, as this quickly turned into show-debugging instead of show-cooking. It was only just right before the end of VCFe 22.0, just before we had to pack everything up, we managed to get the SBC to talk to us via serial:

{{/< tweet user=“Steckschwein” id=“1653060372813733889” >/}}

It’s time for another hardware upgrade. Since we really want to get our single board Steckschwein done, we are going for higher integration of our multiboard prototype. After integrating the UART to the IO-Board, we integrate the OPL2 sound part onto the V9958 video board, so the current Steckschwein multi board incarnations are reduced to three boards. We did postpone our plan to upgrade sound to OPL3 because Daniel Illgen, which we met at VCFb, convinced us with some awesome OPL2 tunes that OPL2 is still cool. Also, we save the extra oscillator, since the OPL2 can be clocked using the CPUCLK-Pin from the V9958, which happens to provide 3.58MHz.

Die neuen IO-Platinen mit integriertem UART sind fertig und haben ihren Weg von China nach München gefunden.

Mit dem neuen Layout hat es nicht nur der UART mit aufs IO-Board geschafft, es sind auch etliche kleinere und größere Verbesserungen eingeflossen:

• Die Joystickports wurden komplett neu designed. Die Optokoppler sparen wir uns, stattdessen wählen wir über einen VIA Pin verschiedene Treiber an, die den gewünschten Joystickport mit VIA Port A verbindet. Die Ports lassen sich auch per Software komplett abschalten, damit der User-Port frei verfügbar ist. Als Schutz für die VIA werden Serienwiderstände verwendet.
• Der SD-Karten-Footprint und der verwendente Slot passen genau zusammen. Das war beim alten Board nicht der Fall. Jetzt sind die Karten- und die Schreibschutzerkennung endlich nutzbar.
• Die Datenpins für die PS/2 Schnittstelle am ATmega8 sind gewandert und liegen jetzt an PD6 und 7. Dadurch sind die RX und TX Pins des USART verfügbar geworden und können nun z.B. für das Debugging des Tastaturcontrollers verwendet werden.
• Zweckmäßigere Plazierung vom SPI-Anschluss des ATmega8 und des freien SPI Ports am Platinenrand. Updates der Tastaturcontrollerfirmware sind nun kein Krampf mehr.
• Der User-Port hat ein besseres Pinout.
• Die neue Platine sieht einfach besser aus. Frisch ausgepackte Platine

Fertig bestückte Platine Die nun obsolet gewordenen Platinen.