GroovyMAME on Raspberry Pi (with GPIO VGA)?

[twistedsymphony]

I was wondering if anyone has got Groovy MAME running on a Raspberry Pi?

I ask because there's this great project that adds VGA support via the GPIO pins:
https://www.raspberrypi.org/blog/gert-vga-adapter/

If GroovyMAME could work with that to output proper 15K video signals then we could essentially have our own GroovyMAME powered X in 1 board.

[Calamity]

Thanks for sharing this, I had no idea this existed. So the Raspberry Pi has finally a VGA output, that's great. I guess GM will suck on the Pi, besides we'd need a new implementation probably to enable custom video. Anyway having an open source device with custom analog video opens lots of possibilities.

[twistedsymphony]

I was doing a bit more research on this after I posted...

There was a kickstarter for the board which got good support and they now have it in production. you can order one here: https://www.pi-supply.com/product/gert-vga-666-hardware-vga-raspberry-pi/

it's actually pretty cheap (then again it's just 2 connectors and 20 some odd resistors)

official git hub: https://github.com/fenlogic/vga666


---------------
Supposedly only works on the B+ variant of the Model 1 Pi

Also works on Model 2 Pis according to some comments here: https://www.raspberrypi.org/forums/viewtopic.php?f=91&t=94424&start=25

[Doozer]

Building MAME for PI2 has already been tested by Steve Boswell (http://choccyhobnob.com/mame-on-raspberry-pi2/)

Unfortunately, the build has been performed without using PI2 architecture optimizations. It is imaginable to have some gain that could bring 100% emulation speed compared to the listed results.

Coming back to groovymame on PI2, I have few questions to be answered first to understand if it is worth the effort. d
a) Is the VGA GPIO driver able to set the dot clock lower as 15kHz?
b) Does the VGA GPIO driver support KMS for resolution switching?
c) What is the CPU utilisation to do the VGA GPIO handling?

[twistedsymphony]

Coming back to groovymame on PI2, I have few questions to be answered first to understand if it is worth the effort. d
a) Is the VGA GPIO driver able to set the dot clock lower as 15kHz?
b) Does the VGA GPIO driver support KMS for resolution switching?
c) What is the CPU utilisation to do the VGA GPIO handling?

from the FAQ:

...From the birth of the Raspberry-Pi there have been complaints about the lack of a VGA output. That
has now been remedied. But only for the B+ and at the cost of losing most of your GPIOs.
The BCM2835 has a parallel display interface on the GPIO pins. I did not publish this in the 2835
datasheet as 50% of the DPI pins where not on the GPIO connector, making it impossible to get any
decent video out. The B+ however has all of the necessary DPI signals brought out. Dom has been
working on the software side and the new DPI (read: VGA) driver software has been added to the
latest release.

Resolution & Quality
The VGA output supports the same resolutions as your HDMI one. Thus from 640x480 up to
1920x1024 60fps. At the highest resolution the pixel quality is almost as good as HDMI.
...
How much CPU power does it use?
Non more than the HDMI output. The video signal is generated by the DPI peripheral, not by bitbashing
the GPIO pins. ...

that definitively answers your question "c" and semi-answers "a" and "b" in that it will likely have the same features/limitations as the HDMI output.

I don't know enough about the Pi's DPI peripheral and associated driver but I would syspect we'd be in a similar situation as a PC where the device is capable but not necessarily designed to output a signal that slow without some modification to the driver.

[Doozer]

Thank you twistedsymphony for the answer. Still an certain level of uncertainty on this VGA output.

Do you know if the HDMI interface is able to sync at lower frequency (15kHz). To my understanding of the PI/PI2 capabilities, 15kHz is not possible on HMDI plug, only on the composite plug.

[twistedsymphony]

I know as much as I've posted in this thread. I would suspect that the graphics chip is the same devices that drives the HDMI and the composite ... and the GPIO pins for VGA and as such would be capable of refresh rates in the 15K range... this is just pure speculation on my part though.

I think the best bet would be to contact the person behind this VGA mod as from what I understand he was one of the original Pi developers who designed the video circuitry. Certain he would know the capabiilty of the system and how they could be adapted to support signals in the 15K and 24K range.

[Calamity]

For me the interesting part about this is not using the Pi for emulation, which is going to suck, but the possibility to use the thing as a video card.