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I use TVP7002 register - clocks per line(39h-3Ah) and lines per frame(37h-38h) to detect what video standard have been capture. And set the related parameters of TVP7002 registers.
It's ok for most of VESA video standard!
But in 1280x768@60 and 1366x768@60, it cant distinguish.
clocks per line: 136
lines per frame: 798
It almost the same.
How can I distinguish?
BTW, I am capturing the VGA source(RGB, VESA standard) and output the 20bit 4:2:2 format embedded sync.
The issue here is most likely that you are using the internal 6.5MHz clock for the timing measurements and this does not have enough resolution/accuracy to determine all possible VESA DMT and CVT modes.
This is why there is also an option to supply an external 27MHz reference clock. This will be both more accurate and have higher resolution than the internal 6.5MHz reference. (See register 1ah bit 3 for reference control)
You can also look at the H & V sync width registers (3bh & 3ch), and the polarity register (14h)
Please note that looking for exact numbers in these registers is risky since there will always be sampling variations and the accuracy of the internal 6.5MHz reference.
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In reply to Steve Clynes:
Thank for quick reply.
It's very useful for me. thanks a lot.
Using a 27MHz reference clock, the clocks per line should be : Pixels per line x 27 MHz / Pixel frequency
1366x768@60 : 1792x27 / 85.5 = 565.895
1280x768@60 : 1664x27 / 79.5 = 565.132
It's almost the same too.
So I will tried to look at the H & V sync width for more information.
In reply to Steven Weng1:
Don't use the character time, use the absolute time since the pixel clock also changes.
1366 normal = 20.959us => count = 5651366 reduced = 20.833us => count = 562
1280 normal = 22.222us => count = 5991280 reduced = 21.099us => count = 569
Thanks a lot.
Sorry, Could you explain more detail?
How to get the absolute time and the related "clocks per line"?
I have read the register clocks per line and 1280x768, 1366x768 both are the same.
The times I listed above came straight from the VESA specification.
If the source video does not conform to the VESA specification then obviously it makes things a lot more difficult.
For VESA compliant signals you should see a difference.
I suggest that you acquire a copy of the VESA DMT and CVT standards which list very clearly and specifically all the timing information that you need to detect standards compliant video signals.
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