Simulating VGA Signal

[hsadan]

Anyone tried simulating a VGA signal using the Arduino?

I'm trying to use the Arduino for something similar to this:
http://www.pyroelectro.com/projects/vga_test_box/index.html

but so far I have yet to succeed. Currently I do have some sort of a signal going, but my timing is off. My LCD monitor seems to detect a signal, and occasionally I get a quick flash of a red on the screen (I currently only have the Red signal driven).

the VGA Test Box (link, above) didn't quite give me enough accurate details, from my initial attempts, and I found the following that helped quite a bit:
http://www-mtl.mit.edu/Courses/6.111/labkit/vga.shtml
http://www.eecg.toronto.edu/~tm4/rgbout.html
http://www.eecg.toronto.edu/~jayar/ece241_05F/vga_new/index.html

I'm still working to try and at least get a steady red (or green/blue) screen signal, but in the meantime I was wondering if anyone here has tried simulating a VGA signal with the Arduino. If you have, any general suggestions/advice?

[mem]

If a PIC can do it at 4MHz then the Arduino chip should have no problem at 16MHz. But the code you linked is in assembler and that application is only driving the VGA outputs. I think you would need to disable the timer0 interrupt (used for the millis counter) and use direct port i/o instead of digital write. It may be difficult getting the timing correct using C function calls so you may need to use assembler.

Good luck!

[hsadan]

yes one problem I initially had was that digitalWrite was too slow, so I switched to using direct port manipulation. I'll try disabling timer0 for more accurate timing.

[westfw]

http://www.serasidis.gr/circuits/AVR_VGA/avr_vga.htm

[dwan]

Hello
I've coded exactly what you're looking for : http://olb7.free.fr/arduino/syncInterrupt.pde

640 * 480 @ 60Hz - FvSync = 60.3 Hz / FhSync = 31.3 kHz
HSync : pin 7 Arduino, pin 13 VGA
VSync : pin 6 Arduino, pin 14 VGA
Arduino's pin 5 is HIGH when video can be sent, LOW otherwise. I use it to power a transistor.

The sync routine is trigged by Timer2. You could achieve a slightly faster sync (31.5kHz) by using Timer1 instead. But it works well !

Keep us posted !

[mem]

dwan, perhaps I am missing something, but it looks like your sketch  is a sync generator but does not generate visible video. I wonder if Lt. Waffles can use your code as a framework and add in the display functionality from the code in westfw's link. What do you think?

BTW, does the millis interrupt on timer0 affected the sync pulse accuracy?

[dwan]

You're right, it only outputs sync signals. Nonetheless, it should be easy to obtain a steady color with minor modifications.

My code is only a stripped-down version of Max Ibragimov's, so it should be ok to display more complex things, if you can understand all Ibragimov's work (that's not my case ). I only took what i needed and understood from his code, given it's not exactly Arduino code and i'm not a skilled coder.

Concerning the accuracy of the sync signal, there is a bit of horizontal jitter. It could be caused by Timer0, i did not tried to stop it. Sometimes the sync is very steady, sometimes it jitters. Actually, i'm trying to cram in the arduino the TLC540 library from acleone, which uses Timer1 & 2 with my code snippet, which I modified to use Timer0. Sadly, i also need a serial link. Each time the arduino receives data, it breaks the VGA sync. For now, i only plan to use 2 168's (one for the sync and the other for serial and TLC stuff), as it only add a few euros to the price of my project.

[mem]

The code in westfw's link handles the serial port just after the vertical sync pulse and before the first visible line so incoming serial data shouldn't affect the display. But that means that the Arduino serial handler has to be disabled and replaced.

After disabling the millis timer and the Serial interrupt handler and using directo port io, there would not be much left of the arduino core code.

[dwan]

Right, that's why i'm looking towards C programming. By handling serial in a non-arduino style, do we lose any critical feature of the arduino?

[mem]

By handling serial in a non-arduino style, do we lose any critical feature of the arduino?

If you use the approach in wesfw's link you lose the Arduino Serial runtime support
My guess is that implementing a vga driver to the OP's requirements would eliminate most of the Arduino functionality. You could use the arduino IDE to create and download the code, but I would think that the running code would not have access to any of the Arduino specific input/output or time functions.

[westfw]

My guess is that implementing a vga driver to the OP's requirements would eliminate most of the Arduino functionality.

I agree; I posted the link as an "existence proof" that it can be done, but generating video from an AVR is very "invasive" - it consumes the majority of the resources of the chip, and any "application" being run would need to be very carefully crafted and probably not very arduino-like.  It might be interesting to see how much could be preserved, though...

[hsadan]

I'm aware that this would use up most of the Arduino's resources - this is going to be an LCD interface module. The only thing I need to try and fit in is to read in a few bytes of data, either through serial or GPIO.

[mem]

The problem is not using up the resources, its that the way the resources are implemented on the arduino that would make the display jumpy. Bypassing the arduino serial port and implementing one that was only active only during the period the video signal was not being displayed (using the logic in the code linked in post #3) would solve this, but it will not be easy to program.

[sascha]

how would I use NTSC for this?

[mem]

You would need to modify the timing for 525 line 60Hz. although the specs for NTSC are easy to find, modifying the code to meet the specs is not a trivial project.