Overflow can put wrong video timings in EDID without any error message

[dreamlayers]

I created an EDID based on

Modeline "1280x960@85R" 146.77 1280 1314 1574 1728 960 961 964 1011 +HSync +VSync

This did not work. The monitor did not sync to it. However, that same mode worked via xrandr. The problem is obvious when the EDID is viewed via edid-decode -X [email protected]:

Modeline "1280x960_84.01" 146.770  1280 1314 1318 1728  960 961 964 1011  +HSync +VSync

Everything matches, but the end of horizontal sync was changed from 1574 to 1318. The horizontal sync pulse is extremely short, from 1314 to 1318, and that is too short. Some overflow caused this to happen, and there was no error message.

Note how verifying the mode via edid-decode -X is useful.

BTW. The mode was customized from 1280x960 85 Hz to match image position on the CRT with other sources. I did not need such a long horizontal sync pulse. So I shortened it, successfully created an EDID based on the following modeline, and got the desired results on the monitor:

Modeline "1280x960_84.01" 146.770  1280 1314 1474 1728  960 961 964 1011  +HSync +VSync