Ok, I tried testing some more Dell monitors and none of them liked 15khz signals.
My methodology is to use an Asus EEE Pc 900A and a few scripts to do cvt and xrandr, running under knoppix 9.1.
The EEEpc 900A has a 4GB ssd and I was able to install a minimal knoppix onto it using the installer script (I think it took < 1GB of space). The full 4.7 gb knoppix wouldn't fit on the 4GB ssd.
I have a few scripts called 240, 292, 800 and 1366. So I can do a quick test with ./240 and ./292 and recover to a "normal" screen resolution with ./800.
240:
#!/bin/bash
xrandr --newmode "720x240_60.00" 13.50 720 744 808 896 240 243 253 256 -hsync +vsyncv
xrandr --addmode LVDS1 "720x240_60.00"
xrandr --output LVDS1 --mode "720x240_60.00"
xrandr --addmode VGA1 "720x240_60.00"
xrandr --output VGA1 --mode "720x240_60.00"
292:
#!/bin/bash
xrandr --newmode "720x292_50.00" 13.50 720 744 808 896 292 295 305 308 -hsync +vsync
xrandr --addmode LVDS1 "720x292_50.00"
xrandr --output LVDS1 --mode "720x292_50.00"
xrandr --addmode VGA1 "720x292_50.00"
xrandr --output VGA1 --mode "720x292_50.00"
and a few to make "normal" resolutions
800:
#!/bin/bash
xrandr --output LVDS1 --mode "800x600"
xrandr --output VGA1 --mode "800x600"
1366:
#!/bin/bash
xrandr --newmode "1368x768_60.00" 85.25 1368 1440 1576 1784 768 771 781 798 -hsync +vsync
xrandr --addmode VGA1 "1368x768_60.00"
xrandr --output VGA1 --mode "1368x768_60.00"
mycvt:
#/bin/bash
echo $1 $2 $3
cvt $1 $2 $3
a=`cvt $1 $2 $3 | tail -1 | cut -d' ' -f2-`
b=`cvt $1 $2 $3 | tail -1 | cut -d' ' -f2`
echo $a
echo $b
xrandr --newmode $a
xrandr --addmode VGA1 $b
xrandr --output VGA1 --mode $b
Mycvt is pretty useful for trying a bunch of different resolutions.
So for example:
mycvt 720 240 60
mycvt 720 292 50
What's kind of interesting is that the dell e2213 doesn't like any resolution with fewer lines than 380. Less than 380 it hates it, but it's interesting that it doesn't have ANY problem with low scan rates.
./mycvt 640 380 40
cvt 640 380 40
# 640x380 39.46 Hz (CVT) hsync: 15.62 kHz; pclk: 12.50 MHz
Modeline "640x380_40.00" 12.50 640 664 720 800 380 383 393 396 -hsync +vsync
./mycvt 720 380 40
cvt 720 380 40
# 720x380 39.46 Hz (CVT) hsync: 15.62 kHz; pclk: 14.00 MHz
Modeline "720x380_40.00" 14.00 720 744 808 896 380 383 393 396 -hsync +vsync
I can go as low as 32 hz but anything less and the asus xrandr won't configure the crtc.
Even though you specify 380 lines, only 350 are actually displayed.
./mycvt 720 380 30
./mycrt 640 380 33
./mycrt 800 380 40
cvt 800 380 40
# 800x380 39.46 Hz (CVT) hsync: 15.62 kHz; pclk: 15.50 MHz
Modeline "800x380_40.00" 15.50 800 824 896 992 380 383 393 396 -hsync +vsync
Sometimes the crtc won't configure properly, so adjusting things a little seems to help, like mycvt 720 380 40 sometimes won't work, but mycvt 728 380 40 will.
The 380 line minimum seems to be a hard limit, anything less and it won't lock. I wish that the firmware could be modified or patched to allow 15khz signals. It wouldn't be a big deal for the monitor makers to enable it. I'd rather have the monitor at least attempt to display a nonstandard resolution than give me an unsupported message.
When you use a 380 line resolution like cvt 728 380 40, the monitor "sees" it as a 350 line mode and reports (640x350 63hz) and will only display 350 lines.
These 3 dell monitors seem to have the same behavior with regard to the 380 line minimum, e2213, p2213 and p2217h.
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Using an ubuntu system, I was able to use a variation of the mycvt script:
This system seems to require executing it twice since the first seems to reset it to 1920x1080. It has a VGA converter on the one of the displayport ports. Note that I changed the output device to DP-2.
#/bin/bash
echo $1 $2 $3
cvt $1 $2 $3
a=`cvt $1 $2 $3 | tail -1 | cut -d' ' -f2-`
b=`cvt $1 $2 $3 | tail -1 | cut -d' ' -f2`
#b=`echo $a|cut -d" " -f1`
echo $a
echo $b
xrandr --newmode $a
xrandr --addmode DP-2 $b
xrandr --output DP-2 --mode $b
a dell s2240 was able to display but nothing lower
mycvt 720 380 49
720 380 49
# 720x380 48.62 Hz (CVT) hsync: 19.25 kHz; pclk: 17.25 MHz
Modeline "720x380_49.00" 17.25 720 744 808 896 380 383 393 396 -hsync +vsync
"720x380_49.00" 17.25 720 744 808 896 380 383 393 396 -hsync +vsync
"720x380_49.00"
