Blow me Down With A Feather: LCD Pal Video Fix!
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Julian Skidmore
Dec 3, 2012, 4:35:06 PM12/3/12
to FIGnition
Hi folks,
Try this version of my current dev .hex file (the ...32.hex version is for people with AtMega328s). A mere hour or less ago, I borrowed an LCD tv from a friend, and like pretty much EVERY FIGnition owner who has tried a FIGnition with an LCD tv I found that with PAL video it gave a really jittery picture. I then tried it with NTSC video and it was steady, but then thought perhaps it's time I tried to tackle the issue.
I remembered that a LONG while back Brian Fairchild from www.minium.co.uk posted on a topic about this very issue. Here's the topic:
https://groups.google.com/d/topic/fignition/BTgtTN801OA/discussion
He said something simple. "The text quoted is wrong... For PAL it is *always* 5 + 5 + 5... A quick web search brings up an amazing number of pages where the information on video sync is just plain wrong."
It turns out he's spot on - my video vertical sync was 6 + 5 + 5, because I was copying all the other intelligent fools who copied the incorrect information in the first place, including Batsocks where I obtained the timing data (though my video generation routine is an independent implementation).
Since Brian hadn't given me an awful lot more information on the subject, I just did a bit more research:
http://www.pembers.freeserve.co.uk/World-TV-Standards/Line-Standards.html#Vertical
And then attempted a correction ......
....
....
AND IT WORKED!!!!
So let's look at the contorted programming changes I needed to fix it - I hope you can get your head around it. The old version of video.h had a line that went:
#define kFrameSyncPreEqual ((kHSyncScanShort+1)*6)
And I changed it to:
#define kFrameSyncPreEqual ((kHSyncScanShort+1)*5)
And now the video looks like this, wonderfully boring scene :-)
http://youtu.be/3WqJiUux7rM
The "World-TV-Standards/Line-Standards.html" link gives you a clue as to where all the 6+5+5 nonsense probably came from: "At the VIth Plenary Meeting of the CCIR in Geneva in 1951 the 625-line standard was specified as having six pre-equalising pulse, six broad field sync pulses and six post-equalising pulses"
Well, I hope you like this little, elaborately named update and the story behind it - AT LAST you may have ROCK-STEADY PAL LCD Video - a 5 minute fix that took 18 months to implement - Enjoy!
-cheers from julz
--
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The DIY 8-bit computer from nichemachines™
Try this version of my current dev .hex file (the ...32.hex version is for people with AtMega328s). A mere hour or less ago, I borrowed an LCD tv from a friend, and like pretty much EVERY FIGnition owner who has tried a FIGnition with an LCD tv I found that with PAL video it gave a really jittery picture. I then tried it with NTSC video and it was steady, but then thought perhaps it's time I tried to tackle the issue.
I remembered that a LONG while back Brian Fairchild from www.minium.co.uk posted on a topic about this very issue. Here's the topic:
https://groups.google.com/d/topic/fignition/BTgtTN801OA/discussion
He said something simple. "The text quoted is wrong... For PAL it is *always* 5 + 5 + 5... A quick web search brings up an amazing number of pages where the information on video sync is just plain wrong."
It turns out he's spot on - my video vertical sync was 6 + 5 + 5, because I was copying all the other intelligent fools who copied the incorrect information in the first place, including Batsocks where I obtained the timing data (though my video generation routine is an independent implementation).
Since Brian hadn't given me an awful lot more information on the subject, I just did a bit more research:
http://www.pembers.freeserve.co.uk/World-TV-Standards/Line-Standards.html#Vertical
And then attempted a correction ......
....
....
AND IT WORKED!!!!
So let's look at the contorted programming changes I needed to fix it - I hope you can get your head around it. The old version of video.h had a line that went:
#define kFrameSyncPreEqual ((kHSyncScanShort+1)*6)
And I changed it to:
#define kFrameSyncPreEqual ((kHSyncScanShort+1)*5)
And now the video looks like this, wonderfully boring scene :-)
http://youtu.be/3WqJiUux7rM
The "World-TV-Standards/Line-Standards.html" link gives you a clue as to where all the 6+5+5 nonsense probably came from: "At the VIth Plenary Meeting of the CCIR in Geneva in 1951 the 625-line standard was specified as having six pre-equalising pulse, six broad field sync pulses and six post-equalising pulses"
Well, I hope you like this little, elaborately named update and the story behind it - AT LAST you may have ROCK-STEADY PAL LCD Video - a 5 minute fix that took 18 months to implement - Enjoy!
-cheers from julz
--
The DIY 8-bit computer from nichemachines™
Rob Fielding
Dec 4, 2012, 10:37:32 AM12/4/12
to fign...@googlegroups.com
Winner!
Rock steady PAL on both my HP and my TV !
Thanks for that moment. It might not exactly be an off-by-one error in the original sense, but it is definitely out by one.
Looking forward to some logo magic when I get home, thanks you guys!
Julian Skidmore
Dec 5, 2012, 9:54:47 AM12/5/12
to fign...@googlegroups.com
Hi folks,
I've updated the firmware images, because the previous one is part of a development build that includes some of the blitter code and I found out that high resolution graphics weren't working for that image. The link for the new firmware image is here:
https://docs.google.com/viewer?a=v&pid=sites&srcid=ZGVmYXVsdGRvbWFpbnxsaWJieThkZXZ8Z3g6NWZlZjJhOTc4Y2Y4YmViMw
Nice huh? It's also attached in this email.
-cheers from julz
I've updated the firmware images, because the previous one is part of a development build that includes some of the blitter code and I found out that high resolution graphics weren't working for that image. The link for the new firmware image is here:
https://docs.google.com/viewer?a=v&pid=sites&srcid=ZGVmYXVsdGRvbWFpbnxsaWJieThkZXZ8Z3g6NWZlZjJhOTc4Y2Y4YmViMw
Nice huh? It's also attached in this email.
-cheers from julz
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