VGADB(6)VGADB(6)NAMEvgadb - VGA controller and monitor database
The VGA database, /lib/vgadb, consists of two parts, the first describ‐
ing how to identify and program a VGA controller and the second
describing the timing parameters for known monitors to be loaded into a
VGA controller to give a particular resolution and refresh rate. Con‐
ventionally, at system boot, the program aux/vga (see vga(8)) uses the
monitor type in /env/monitor, the display resolution in /env/vgasize,
and the VGA controller information in the database to find a matching
monitor entry and initialize the VGA controller accordingly.
The file comprises multi-line entries made up of attribute/value pairs
of the form attr=value or sometimes just attr. Each line starting
without white space starts a new entry. Lines starting with # are com‐
The first part of the database, the VGA controller identification and
programming information, consists of a number of entries with attribute
ctlr and no value. Within one of these entries the following
attributes are meaningful:
nnnnn an offset into the VGA BIOS area. The value is a string
expected to be found there that will identify the controller.
For example, 0xC0068="#9GXE64 Pro" would identify a #9GXEpro VGA
controller if the string #9GXE64 Pro was found in the BIOS at
address 0xC0068. There may be more than one identifier
attribute per controller. If a match cannot be found, the first
few bytes of the BIOS are printed to help identify the card and
create a controller entry.
A range of the VGA BIOS area. The value is a string as above,
but the entire range is searched for that string. The string
must begin at or after nnnnn and not contain any characters at
or after mmmmm. For example, 0xC0000-0xC0200="MACH64LP" identi‐
fies a Mach 64 controller with the string MACH64LP occurring
anywhere in the first 512 bytes of BIOS memory.
ctlr VGA controller chip type. This must match one of the VGA con‐
troller types known to /dev/vgactl (see vga(3)) and internally
to aux/vga. Currently, ark2000pv, clgd542x, ct65540, ct65545,
cyber938x, et4000, hiqvideo, ibm8514, mach32, mach64, mach64xx,
mga2164w, neomagic, s3801, s3805, s3928, t2r4, trio64, virge,
vision864, vision964, vision968, and w30c516 are recognized.
ramdac RAMDAC controller type. This must match one of the types known
internally to aux/vga. Currently att20c490, att20c491,
att20c492, att21c498, bt485, rgb524mn, sc15025, stg1702,
tvp3020, tvp3025, and tvp3026 are recognized.
clock clock generator type. This must match one of the types known
internally to aux/vga. Currently ch9294, icd2061a, ics2494,
ics2494a, s3clock, tvp3025clock, and tvp3026clock are recog‐
hwgc hardware graphics cursor type. This must match one of the types
known to /dev/vgactl and internally to aux/vga. Currently
ark200pvhwgc, bt485hwgc, clgd542xhwgc, clgd546xhwgc,
ct65545hwgc, cyber938xhwgc, hiqvideohwgc, mach64xxhwgc,
mga2164whwgc, neomagichwgc, rgb524hwgc, s3hwgc, t2r4hwgc,
tvp3020hwgc, and tvp3026hwgc are recognized.
membw Memory bandwidth in megabytes per second. Vga chooses the high‐
est refresh rate possible within the constraints of the monitor
(explained below) and the card's memory bandwidth.
linear Whether the card supports a large (>64kb) linear memory window.
The value is either 1 or 0 (equivalent to unspecified). The
current kernel graphics subsystem requires a linear window;
entries without linear=1 are of historic value only.
link This must match one of the types known internally to aux/vga.
Currently vga and ibm8514 are recognized. The type vga handles
generic VGA functions and should almost always be included. The
type Ibm8514 handles basic graphics accelerator initialization
on controllers such as the early S3 family of GUI chips.
The clock, ctlr, link, and ramdac values can all take an extension fol‐
lowing a '-' that can be used as a speed-grade or subtype; matching is
done without the extension. For example, ramdac=stg1702-135 indicates
the STG1702 RAMDAC has a maximum clock frequency of 135MHz, and
clock=ics2494a-324 indicates that the frequency table numbered 324
should be used for the ICS2494A clock generator.
The functions internal to aux/vga corresponding to the clock, ctlr,
link, and ramdac values will be called in the order given for initial‐
ization. Sometimes the clock should be set before the RAMDAC is ini‐
tialized, for example, depending on the components used. In general,
link=vga will always be first and, if appropriate, link=ibm8514 will be
The entries in the second part of /lib/vgadb have as attribute the name
of a monitor type and the value is conventionally a resolution in the
form XxY, where X and Y are numbers representing width and height in
pixels. The monitor type (i.e. entry) include has special properties,
described below and shown in the examples. The remainder of the entry
contains timing information for the desired resolution. Within one of
these entries the following attributes are meaningful:
clock the video dot-clock frequency in MHz required for this resolu‐
tion. The value 25.175 is known internally to vga(8) as the
baseline VGA clock rate. defaultclock the default video dot-
clock frequency in MHz used for this resolution when no memory
bandwidth is specified for the card or when vga cannot determine
the maximum clock frequency of the card.
shb start horizontal blanking, in character clocks.
ehb end horizontal blanking, in character clocks.
ht horizontal total, in character clocks.
vrs vertical refresh start, in character clocks.
vre vertical refresh end, in character clocks.
vt vertical total, in character clocks.
hsync horizontal sync polarity. Value must be + or -.
vsync vertical sync polarity. Value must be + or -.
interlaced mode. Only value v is recognized.
alias continue, replacing the alias line by the contents of the entry
whose attribute is given as value.
continue, replacing this include line by the contents of the
previously defined include monitor type with matching value.
(See the examples.) Any non-zero attributes already set will
not be overwritten. This is used to save duplication of timing
information. Note that value is not parsed, it is only used as
a string to identify the previous include=value monitor type
The values given for shb, ehb, ht, vrs, vre, vt, hsync, and vsync are
beyond the scope of this manual page. See the book by Ferraro for
Basic ctlr entry for a laptop with a Chips and Technology 65550 con‐
ctlr # NEC Versa 6030X/6200MX
0xC0090="CHIPS 65550 PCI & VL Accelerated VGA BIOS"
A more complex entry. Note the extensions on the clock, ctlr, and ram‐
dac attributes. The order here is important: the RAMDAC clock input
must be initialized before the RAMDAC itself. The clock frequency is
selected by the ET4000 chip.
ctlr # Hercules Dynamite Power
0xC0076="Tseng Laboratories, Inc. 03/04/94 V8.00N"
Monitor entry for type vga (the default monitor type used by vga(8))
and resolution 640x480x.
include = 640x480@60Hz # 60Hz, 31.5KHz
shb=664 ehb=760 ht=800
vrs=491 vre=493 vt=525
vga = 640x480 # 60Hz, 31.5KHz
Entries for multisync monitors with video bandwidth up to 65MHz.
# Multisync monitors with video bandwidth up to 65MHz.
multisync65 = 1024x768 # 60Hz, 48.4KHz
multisync65 = 1024x768i # 87Hz, 35.5KHz (interlaced)
Note how this builds on the existing vga entries.
SEE ALSOndb(2), vga(3), ndb(6), 9boot(8), vga(8)
Richard E. Ferraro, Programming Guide to the EGA, VGA and Super VGA
Cards, Third Edition
The database should provide a way to use the PCI bus as well as BIOS
memory to identify cards.
ADDING A NEW MONITOR
Adding a new monitor is usually fairly straightforward, as most modern
monitors are multisync and the only interesting parameter is the maxi‐
mum video bandwidth. Once the timing parameters are worked out for a
particular maximum video bandwidth as in the example above, an entry
for a new monitor with that limit is simply
# Sony CPD-1304
# Horizontal timing:
# Allowable frequency range: 28-50KHz
# Vertical timing:
# Allowable frequency range: 50-87Hz
Even this is not necessary, as the monitor type could simply be given
ADDING A NEW VGA CONTROLLER
While the use of this database formalizes the steps needed to program a
VGA controller, unless you are lucky and all the important components
on a new VGA controller card are interconnected in the same way as an
existing entry, adding a new entry requires adding new internal types
to vga(8). Fortunately, the unit of variety has, for the most part,
shifted from individual components to entire video chipsets. Thus in
lucky cases all that is necessary is the addition of another 0xNNNNN=
line to the entry for the controller. This is particularly true in the
case of the ATI Mach 64 and the S3 Virge.
If you need to actually add support for a controller with a different
chipset, you will need the data sheets for the VGA controller as well
as any RAMDAC or clock generator (these are commonly integrated into
the controller). You will also need to know how these components
interact. For example, a common combination is an S3 86C928 VGA chip
with an ICD2061A clock generator. The ICD2061A is usually loaded by
clocking a serial bit-stream out of one of the 86C928 registers. Simi‐
larly, the RAMDAC may have an internal clock-doubler and/or pixel-mul‐
tiplexing modes, in which case both the clock generator and VGA chip
must be programmed accordingly. Hardware acceleration for rectangle
fills and block copies is provided in the kernel; writing code to han‐
dle this is necessary to achieve reasonable performance at high pixel