How sensitive is DDC to things like the video cable or the presence of
KVM switches? I just encountered a situation where DDC worked
randomly when run through a KVM but worked fine when directly
connected to the monitor. I've never seen any problem like this with
30 previous identical machines plugged into the same KVM. (I can tell
it doesn't work because without it, the DPI defaults to 75 which makes
the fonts come out too small.) OS is stock Red Hat 7.2 with updates,
XFree 4.1.0 plus whatever Red Hat does to it. Hardware is an Nvidia
GF2Ultra. I'm running the nv driver, not the binary Nvidia one.
I thought that DDC was just a low speed serial connexion and thus
should be pretty robust. I notice no loss of video clarity and no
noise through the KVM, so perhaps it's much more sensitive than I
believed.
For completeness, here's a diff of two logs: one where DDC worked and
another where it didn't:
--- b Wed Apr 10 17:22:27 2002
+++ c Wed Apr 10 17:22:44 2002
@@ -9,7 +9,7 @@
Build Host: stripples.devel.redhat.com
Module Loader present
-(==) Log file: "/var/log/XFree86.0.log", Time: Wed Apr 10 17:22:16 2002
+(==) Log file: "/var/log/XFree86.0.log", Time: Wed Apr 10 17:22:36 2002
(==) Using config file: "/etc/X11/XF86Config-4"
Markers: (--) probed, (**) from config file, (==) default setting,
(++) from command line, (!!) notice, (II) informational,
@@ -321,58 +321,6 @@
(II) NV(0): I2C bus "DDC" initialized.
(II) NV(0): I2C device "DDC:ddc2" registered.
(II) NV(0): I2C device "DDC:ddc2" removed.
-(II) NV(0): I2C device "DDC:ddc2" registered.
-(II) NV(0): I2C device "DDC:ddc2" removed.
-(II) NV(0): DDC Monitor info: 0x84d1328
-(II) NV(0): Manufacturer: SNY Model: 290 Serial#: 8045784
[...] (DDC stuff elided for brevity)
-(II) NV(0): Ranges: V min: 48 V max: 120 Hz, H min: 30 H max: 107 kHz, PixClock max
350 MHz
-(II) NV(0): Monitor name: SONY CPD-G400
-(II) NV(0): Serial No: 8045784
-(II) NV(0): end of DDC Monitor info
-
(==) NV(0): Using gamma correction (1.0, 1.0, 1.0)
(II) NV(0): SONY CPD-G40: Using hsync range of 30.00-107.00 kHz
(II) NV(0): SONY CPD-G40: Using vrefresh range of 48.00-120.00 Hz
@@ -382,8 +330,7 @@
(--) NV(0): Virtual size is 1280x1024 (pitch 1280)
(**) NV(0): Default mode "1280x1024": 157.5 MHz, 91.1 kHz, 85.0 Hz
(II) NV(0): Modeline "1280x1024" 157.50 1280 1344 1504 1728 1024 1025 1028 1072
+hsync +vsync
-(--) NV(0): Display dimensions: (37, 27) cm
-(--) NV(0): DPI set to (87, 96)
+(==) NV(0): DPI set to (75, 75)
(II) Loading sub module "fb"
(II) LoadModule: "fb"
(II) Loading /usr/X11R6/lib/modules/libfb.a
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