[Openchrome-users] VT1625 NTSC Modes

[Joel Means]

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I am looking for a little help.  I have tried to patch the via_vt162x.h
file to add a mode for 640x480Over and to fix the 640x480 mode for the
TV-out on my EN12000 board (CN700 chipset).  So I copied the register
values from Via's code into the Openchrome code.  Then I copied the
modeline from the vt1622 table.  The output on S-Video is close to
right.  It is offset quite a bit to the left, but I know that is just a
modeline problem that I should be able to tweak.  The other issue I have
is that the image jumps up and down rapidly.  It almost seems as if the
A and B fields are being drawn in different places.  Now, I don't know a
whole lot about what all of the register values do and I have read the
Xf86 guide to modelines, but that is all a bit fuzzy still.  So my
question is, is the jumpy problem a modeline issue or a problem with the
registers?  I am not sure what to tweak.  Any guidance would be greatly
appreciated.
Thanks,
Joel

P.S. Can anyone tell me how the modeline values given in the Via code
relate to those in the Openchrome code?  I am having a little trouble
seeing the correlation.  Below is an excerpt from each.

Via (640x480 underscan for vt1622):
  /* HT,  HA, HBS, HBE, HSS, HSE,  VT,  VA, VBS, VBE, VSS, VSE */
    784, 640, 640, 144, 656,  56, 600, 480, 480, 120, 488, 7

Openchrome (should be the same mode for vt1622):
{ MODEPREFIX("640x480"),        23520,  640,  656,  744,  784, 0,  480,
 487,  491,  600, 0, V_NHSYNC | V_NVSYNC, MODESUFFIXNTSC }
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