The latest update in the Veronica 6502 computer project is this finalized VGA board which now has a home in the machine’s backplane.
We’ve been glued to the updates [Quinn Dunki] has been posting about the project for many months now. Getting the GPU working proved to take quite a bit of time, but we learned a ton just by following along. The video output had humble beginnings way back in March. That breadboarded circuit got complicated very quickly and that was before it was even interfaced with the CPU. As you can see from the image above, etching and populating the GPU board really cleans up the build. We’re sure it’s robust enough to move around at this point. We wonder if she’s planning on showing it off at a Maker Faire or another geeky gathering?
It really has become clear how wise [Quinn] was to design a backplane board early on. It plays right into the modular concept. She was even smart enough to include that SIL pin header on the near side of the board which was used heavily while prototyping this video module.
If you’re working with a CGA, EGA, or RGB gaming system this inexpensive board does a great job of converting the signal to VGA so that you can play using a modern display. But what if you have a SCART connector as an output? That’s the situation in which [EverestX] found himself so he hacked in SCART support.
The first step is to source a female SCART connector. He grabbed a coupler off of eBay and cracked it open, yielding two connectors. Now comes the wiring and you may have already noticed that there’s a lot more going on here than the color channels, sync signal, and ground. Technically that’s all you really need to make this happen, but the results will not be good. First off, the sync signal for SCART tends to be rather awful. That’s where the blue breakout board comes into play. [EverestX] used an LM1881 to grab the composite sync (yes, composite sync, not component sync) signal as a feed for the VGA converter. He also added in an audio jack for the sound that is coming through the connector.
[Quinn Dunki] just moved to a new work space and had to pack up her homebrew computer project — called Veronica — in the process. She just unboxed it again and decided now was a good time to fortify the VGA display hardware. It wasn’t in the greatest of shape, since everything for the initial video tests had been built on a breadboard. The transition to protoboard ended up turning out just swell.
One of the thing’s that we like best about [Quinn’s] hacks is that she documents her failures (or perhaps we should just call them hiccups?) just as much as she does her successes. This is not a small thing. We understand, because our own screw-ups don’t usually get photographed due to our raging need to just make the frakking thing work.
Once she had moved all the components to the new board the circuit was amazingly organized. Since she’s doing high-speed switching with the VGA signals it was important to keep the lines as short and straight as possible, hence the SRAM stack seen above. But when it was first fired up she had a jumble of only-somewhat-organized color stripes. It turns out that she had forgotten to change the color register in the AVR code, the color lines were hooked up in the wrong order, and the switch mode supply was injecting noise into the system. But thanks to her documentation of these issues we’ll know what to do when we find ourselves in a similar situation.
It’s fairly easy to create VGA with an FPGA using a simple R/2R DAC. As [Mike] points out, this requires a lot of IO pins, and many development boards only support 8 bit VGA. Analog VGA is being replaced with DVI-D and HDMI on many devices nowadays, so it would be nice to port projects from VGA to DVI-D.
To address this, he’s come up with a simple DVI-D implementation in VHDL. The result converts RGB and sync data for VGA into DIV-D. Since DVI-D and HDMI both use the same signals for video, this can be connected to either input on a monitor or TV.
This implementation is shown displaying a test pattern on the Pipistrello development board, which features a Spartan 6 LX45 FPGA, but the project was written to be portable to other vendor’s FPGAs. With the right connector and a fast enough clock speed, this project should help move a project from 8 bit VGA to glorious 32 bit color.
We can’t say the name rolls off the tongue, but it is beginning to look like the OlinuXino is going to happen. Here you can see the prototype hardware booting Android. If this is the first time you’re seeing the hardware you can think of it in the same category as the Raspberry Pi. It’s a butt-kicking ARM platform that comes as a bare-board with which you can do what you please.
Olimex Ltd. put together the offering, which seems to be part of the name mash-up (Olimex + Linux + Arduino?). The board hosts an ARM Cortex-A8 processor which runs at 1 GHz. There’s a half a gigabyte of ram, four USB and one USB-OTG ports, and a big array of breakout pins. One eyebrow-raising choice was not to include an HDMI connector. Instead the board offers VGA and Audio outputs. There is a pin header meant for an LCD screen, as seen in the image above, so it could be that the intention here is for smaller or more portable applications. But like we said, the form factor really lets you do what you want.
Possibly the best part is the price. The target for the top-of-the-line board is 55 Euros (about $68) and that comes with WiFi and 4 GB of NAND storage on the board. There’s a bunch of posts on the project, including a look at the PCB routing work. This link to the A13 tag will give you the widest overview of the work so far.
[Alessandro] sent us a link to his post about a PRU software VGA rasterizer. It’s not the easiest read, but we think it’s worth your time.
The gist of his background information is that back when his company was developing for an ARM9 processor he wanted to test his mettle with the coprocessor chips. The first iteration was to write a character LCD driver that pulled data from the main processor’s memory and displayed it on the screen. This makes for a low-overhead debugger display, it’s also very limited (32 characters over two lines doesn’t tell you much). And thus began his work on a VGA generator for the Programmable Realtime Unit (PRU is what TI calls this coprocessor) that grabs data in memory just like the original version. But with a much larger display area this becomes quite useful for debugging. That resistor mess is the R2R ladder he soldered together to perform the Digital to Analog Conversions. There’s a quick demo clip after the jump.
This work could end up being useful to you. [Alessandro] reports that the BeagleBone has similar hardware. A bit of porting could get his generator working on that board as well.
Continue reading “Offloading VGA generation onto a coprocessor”