Raspberry Pi program to clone HDMI output to GERT666 VGA
We all love the Raspberry Pi, but it lacks VGA output, which is outdated but fitting for MANY of the crazy ideas you can come up with this wonderful system. Gert van Loo solved this issue when he gave us the GERT666, a passive board which helps you map the GPIO to a VGA output. It works like a charm but is has one short-comming: You have to either pick the VGA or the HDMI display. (Except if you want to play videos using omxplayer https://github.com/huceke/omxplayer or specially compiled Qt apps: https://www.raspberrypi.org/forums/viewtopic.php?t=135629&p=902277)
Now, with this little program you can clone your screen. It's not as good as two independent screens, but hopefully this program will get the ball moving.
To get the GERT666 running you must download https://github.com/fenlogic/vga666/blob/master/setup/dt-blob-dpi.bin
and move it to /boot/dt-blob.bin . Then edit the /boot/config.txt file adding the following lines:
dtoverlay=vga666
enable_dpi_lcd=1
display_default_lcd=0
The first two lines enable the GERT666, but the last line sets your HDMI display as default.
Finally, disable SPI and I2C interfaces (and I think the Serial Console) through raspi-config and reboot.
To get the same output on your GERT666 you must then run ./cloner.bin .
To get this program on your system just download this repository and make, then run ./cloner.bin
and you should get the same image on both screens.
-help | -h:Displays help and flag information.-displaySrc:ID of the source display. (Default: 0)-displayDst:ID of the destination display. (Default: 4)-framePeriod:Delay between frames in milliseconds. (Default: 15)
This program works by taking a snapshot from the current output and setting it as the output for the VGA display. As far as I understand, all is done on the GPU so CPU overhead should be minimal. This program is inspired by https://github.com/tasanakorn/rpi-fbcp/ . Also, dispmanx.c was of great help as documentation on the GPU API is... incomplete.
Being honest, my C skillz are non-existant so please please send any changes you would like to publish. Also, an idea that might work is to configure the framebuffer to be as big as the two screens together, fiddle a bit with the configuration of this program to copy only the second screen portion and then we should be able to get the independent dual screen setup! (I think)