how does FRQA really works with Video drivers?
by, 01-03-2014 at 02:43 PM (623 Views)
I am trying to do my own video driveer for VGA. I read all datasheets, propeller manual, I already saw other drivers but looks like nobody does what the datasheet says...
this is what I am doing right now. I tryed to do a simple program to make one single line of video first, so there is no monitor connected, no vertical signal yet, just an oscilloscope to see the times and figure how and where do the other's drivers got their weird numbers for FRQA, VSCL, PIXELS and COLORS and , so I first setup the video generator in two color mode and other registrs like this:
_FRQA = 40000000;
_CTRA = 0b00001 <<26 | 0b101 <<23;
_VCFG = 0b01 <<29 | 0b0 <<28 | 0b010 <<9 | 0xFF ;
_VSCL = 1<<12 | 32;
//Hsync and back porch
__builtin_propeller_waitvid( 0x00000200, 0xfc1fffff);
for(i = 0; i < 16; i++)
__builtin_propeller_waitvid( 0x0000c202, 0xaaaaaaaa);
You can see the behavior of this small portion of code in the attached image, so I was very happy since it is too simple to make a video driver, I started to "calibrate" the times by changing the FRQA to adjust my line of video to comply the VGA standars and there is what I got.
I have seen other drivers which works perfectly with FRQA adjusted to _FRQA = 0x1C000000; so I changed in the code above for this value and the signals gone with a mess in the whole port, see the attached image...
I want to ask what happens there? I was incrementing this FRQA litle by litle and the times of my Hsync and pixels signals get narrower as expected but sudenly it stops to do the proper behavior, so I cannot get how the other driver came with this value??
Can somebody help me?