Flickering with an Arduino1284p

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What steps will reproduce the problem?

1. Build an atmega1284p minimal system
2. Upload DemoNTSC sketch
3. See TV

What is the expected output? What do you see instead?

Using the last release (TVout_w_audio.zip) I see an occasional horizontal 
flickering.

Using the library shipped with the Video Game Shield, the last line in 
version_history is: R6 (June 2010) (Currently Beta at 5.9), I see the same kind 
of flickering but constantly. 

What version of the product are you using? On what operating system?

Arduino software version 0021 version on Linux.

Please provide any additional information below.

I had attached a picture of my TV, the flickering is the same in both cases but 
almost all the time with the R6 and occasionally with the TVout_w_audio release.

I also noticed how the pins changes from the TVout_w_audio to the R6 release 
(the ones triggered with the ENABLE_FAST_OUTPUT).

Finally, I tired to use the source from your repository but it can't complie 
the DemoNSTC sketch.

Original issue reported on code.google.com by man...@rabade.com on 24 Nov 2010 at 7:31

Attachments:

• tv-out-atmega1284.jpg

[GoogleCodeExporter]

A couple of notes i forgot: 

- My ATmega1284p is running at 16Mhz
- The output I attached is not from the DemoNTSC, is another example I created 
that draws a rectangle with a cross between its corners, you can see that the 
image is also drawn with a horizontal offset (thats the flickering).
- I had tired the example sketches and schematic with an Arduino Duemilanove 
(ATmega328p) with both version and it works fine

Original comment by man...@rabade.com on 24 Nov 2010 at 6:47

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I have a atmega1284p as well and I also have troubles with it.  The issue 
varies depending on the resolution used. from unusable to almost non 
existent(120x96 works pretty well).

The issue is caused by the line handler taking to long on the 1284p vs other 
devices. It can be fixed by changing 
_NTSC_TIME_OUTPUT_START/_PAL_TIME_OUTPUT_START to a slightly higher value (15 
for NTSC and 15.5 for PAL seem to work perfectly although this may shift the 
image of the screen....)

Are you using the sanguino cores? I am wondering if there is an interrupt 
firing that cannot for this library to work. Although I have not heard of this 
issue effecting standard sanguinos.

Original comment by mdmetzle@gmail.com on 25 Nov 2010 at 1:24

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Demo sketches work fine for me although maybe I have fixed them since the last 
push. Ill look into it.

Original comment by mdmetzle@gmail.com on 25 Nov 2010 at 1:25