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<article>

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<title> Information for Cirrus Chipset Users
<author> Harm Hanemaayer (<it>hhanemaa@cs.ruu.nl</it>),
         Randy Hendry (<it>randy@sgi.com</it>)
<date> 27 January 1995

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<toc>

<sect> Supported chipsets <p>

There are two different SVGA drivers for Cirrus chipsets, one called
``cirrus'' and one called ``cl64xx''.
The ``cirrus'' driver is used in the 256-color SVGA server (with
acceleration) and the mono server (without acceleration). The SVGA server
supports 16 and 32 bits-per-pixel truecolor modes on some configurations.
The ``cl64xx'' driver is used in the 256-color SVGA, 16-color and mono
servers.  Note that except where stated otherwise, this document is
referring to the ``cirrus'' driver.
The following chipsets by Cirrus Logic are supported:
<descrip>
<tag>CL-GD5420</tag>
	ISA SVGA chipset, 1Mbyte; maximum dot clock is 45 MHz (256
	color server). Acceleration with extended write modes (used
	for scrolling and solid filling in this driver). This chipset
	can <em>not</em> support 1024x768 non-interlaced in 256 colors.
<tag>CL-GD5422</tag>
	Enhanced version of the 5420 (32-bit internal memory
	interface). Maximum dot clock is 80 MHz.
<tag>CL-GD6205/6215/6225/6235</tag>
	Laptop chipsets more or less compatible with the 5420. The
	only dot clock supported is 25 MHz (more on an external
	display). Some problems have been reported with these
	chipsets (especially on external displays). Take note of
	the "<tt>noaccel</tt>" option.
<tag>CL-GD6420/6440</tag>
	These chipsets are not compatible with the 542x series, but are
        supported by the ``cl64xx'' driver. It is used in
        recent laptops, and bears some similarity to old Cirrus
        chipsets (5410/AVGA2). The driver may also work for other
        64xx chips. The configuration identifiers for this driver are
	"<tt>cl6420</tt>" and <tt>"cl6440"</tt>.  This driver is discussed
	in detail in section <ref id="cl64xx" name="The cl64xx Driver">.
<tag>CL-GD5424</tag>
	Basically VLB version of the 5422, but resembles the
	5426 in some respects.
<tag>CL-GD5426</tag>
	Supports both ISA bus and VLB, and up to 2Mbyte of memory.
	Has BitBLT engine for improved acceleration (BitBlt, image
	transfer, text). Dot clock limit is 85 MHz.
<tag>CL-GD5428</tag>
	Enhanced version of the 5426.
<tag>CL-GD5429</tag>
	Enhanced version of the 5428; officially supports higher
	MCLK and has memory-mapped I/O.
<tag>CL-GD5430</tag>
	Similar to 5429, but with 543x core (32-bit host interface).
	Does not have 64-bit memory mode.
<tag>CL-GD5434</tag>
	Next generation `Alpine' family chip with 64-bit internal
	memory interface. Used by the Orchid Kelvin 64. The chip
	can only support 64-bit mode if equipped with 2 Mbytes of
	memory; cards with only 1 Mbyte are severely limited.
	Support dot clocks up to 110 MHz.
</descrip>

Here's a list of maximum dot clocks for each supported depth:

<quote><verb>
                mono        8 bpp (256c)    16 bpp____      32 bpp
CL-GD62x5       45 MHz      45 MHz____
CL-GD5420       80 MHz      45 MHz (1)
CL-GD542x/512K  80 MHz      45 MHz____
CL-GD5422/24    80 MHz      80 MHz____      40 MHz____
CL-GD5426/28    85 MHz      85 MHz____      45 MHz (2)
CL-GD5429       85 MHz      85 MHz____      50 MHz____
CL-GD5430       85 MHz      85 MHz____      45 MHz (2)
CL-GD5434/1Mb   85 MHz      85 MHz____      45 MHz (2)
CL-GD5434/2Mb   85 MHz      85 MHz____      85 MHz____      45 MHz (2)

(1) with 512K memory.
(2) 50 MHz with high MCLK setting.
</verb></quote>

Rough virtual/physical screen resolution limits for different amounts of
video memory:
<quote><verb>
            mono          8bpp          16 bpp        32 bpp
256K_       800x600__     640x400__     _________     ________
512K_       1152x900_     800x600__     640x400__     ________
1024K       1600x1200     1152x900_     800x600__     ________
2048K       2304x1728     1600x1200     1152x900_     800x600_
4096K       2304x1728     2272x1704     1600x1200     1152x900
</verb>
</quote>
The virtual width must be a multiple of 32 if acceleration is used.
The horizontal monitor timings must be below 2048.

To run <tt>XF86_SVGA</tt> at 16 or 32 bpp, pass options to the X server as
follows:
<verb>
startx -- -bpp 16		5-6-5 RGB ('64K color', XGA)
startx -- -bpp 16 -weight 555	5-5-5 RGB ('Hicolor')
startx -- -bpp 32		8-8-8 XRGB truecolor (5434)
</verb>


<sect> Basic configuration <p>

It is recommended that you generate an XF86Config file using the
`<tt>xf86config</tt>' program, which should produce a working
high-resolution 8bpp configuration. You may want to include mode
timings in the <tt>Monitor</tt> section that better fit your monitor
(e.g 1152x900 modes). The driver options are described in detail in
next section; here the basic options are hinted at.

For all chipsets, a <tt>Clockchip &dquot;cirrus&dquot;</tt> line in the
<tt>Device</tt> section can be useful. This allows the use of any dot
clocks, instead of one out of the fixed set of dot clocks supported
by the driver. This is required if you want a 12.6 MHz dot clock for
low-resolution modes.

If graphics redrawing goes wrong, first try the
<tt>&dquot;no_bitblt&dquot;</tt>
option if your chip has the BitBLT engine, if that doesn't work, try the
<tt>&dquot;noaccel&dquot</tt>; option, which disables all accelerated
functions. The <tt>&dquot;no_imageblt&dquot;</tt> option may be sufficient.

In order to be able to run at a depth of 16bpp and 32bpp, and to improve
performance at 8bpp, linear addressing must be enabled. This is generally
possible on 543x local bus cards, and if you have less than 16Mb of system
memory, on local bus 542x cards and ISA 543x cards. You must specify
the <tt>&dquot;linear&dquot;</tt> option and possibly a <tt>Membase</tt>
address. See the following sections for a detailed description.

Lastly, on the 543x, it is advisable to use the <tt>&dquot;mmio&dquot;</tt>
option in the Device section for better acceleration (this might also apply
to the 5429, which has not been tested).

<sect> XF86Config options <p>
Don't use the `<tt>Clocks</tt>' command. The clocks are fixed
(i.e. not probed), and
there should be no variation between cards (other than the maximum supported
clock for each chipset).

The following options are of particular interest to the Cirrus driver. Each
of them must be specified in the `<tt>svga</tt>' driver section of the
<tt>XF86Config</tt>
file, within the <tt>Screen</tt> subsections of the depths to which they are
applicable (you can enable options for all depths by specifying them in the
Device section).
<descrip>
<tag>Option &dquot;noaccel&dquot;</tag>
	This option will disable the use of any accelerated functions. This
	is likely to help with some problems related to DRAM timing,
	high dot clocks, and bugs in accelerated functions, at the cost
	of performance (which will still be reasonable on VLB).
<tag>Option &dquot;fast_dram&dquot; &dquot;med_dram&dquot; \
&dquot;slow_dram&dquot; (5424/6/8/9, 543x)
</tag>
	The <tt>"fast_dram"</tt> option will cause the driver to set the
	internal
	memory clock (MCLK) register of the video card to a higher value.
	Normally, this register is not touched but it appears that the
	standard CL-GD542x BIOS initializes it to a value that is somewhat
	on the low side (limited by the chip specification), which has a
	negative influence on performance of high dot clock modes. This
	is especially true if extended RAS timing is being used (this is
	indicated in the server probe).
	The actual speed of DRAM is not a critical factor in the determining
	whether	this option is appropriate; one card with 80ns DRAM using
	Extended RAS timing, which came with a DOS driver utility to set the
	MCLK to this value (0x22), seems to run stable at higher MCLK.

	There are also (mainly brand name) cards whose customized BIOS does
	initialize to a higher non-standard value. In this case, the
	use of this option is probably not appropriate.

	The <tt>"slow_dram"</tt>
	option will set the MCLK to the value used by the
        standard CL-GD542x BIOS (0x1c). Symptoms of a MCLK that is too high
        can be vertical bands of flickering pixels on the screen, erroneous
        pixels appearing in text, and loosing pixels in the textmode font
        after running X (note that very similar effects can be caused by an
        MCLK setting that is too low).

	Upon start-up, the driver will report the value of the MCLK
	register (check this first), and also any changes that are made.

	Typical MCLK values:
	<descrip>
	<tag/0x1c (50 MHz)/
		This is usually the BIOS default.
		It is forced by the <tt>"slow_dram"</tt> option.
	<tag/0x1f (55 MHz)/
		Value used by the <tt>"med_dram"</tt> option.
		Highest value that
		542x based cards seem to be able to handle with linear
		addressing enabled.
	<tag/0x22 (60 MHz)/
		Value that most (Extended RAS) 542x cards seem to be able to
		handle, used by	the <tt>"fast_dram"</tt> option.
	</descrip>

	The official maximum of the 542x chips is 50 MHz.
	The official spec. for the 5434 is also 50 MHz (0x1c)
	and that for
        the 5429 and 5430 is probably 60 MHz (0x22). Current revisions
	of the 5434 (E and greater) support 60 MHz MCLK in graphics modes,
	and the driver will program this automatically. If it causes
	problems, use the "slow_dram" option.

	The driver takes the MCLK into account for clock limits that
	are determined by DRAM bandwidth.

	If you are not having any problems (performance or stability at
	high dot clocks), it is best not to use the "<tt>fast_dram</tt>"
	option.
<tag>
Option &dquot;no_bitblt&dquot;
</tag>
	This option, when used with a 5426/28/29/3x, will have the effect of
        disabling the use of the BitBLT engine (which the 5424 does not
        have), while retaining some acceleration. This will be useful for
        problems related to functions that use the BitBLT engine.
<tag>
Option &dquot;no_imageblt&dquot;
</tag>
	This option, when used with a 5426/28/29/3x, will have the effect of
        disabling the use of BitBLT functions that go from system memory
        to video memory. This is useful for problems relating to image
        write, such as a little white line at the top left corner of the
        screen, or a skewed image after a console switch back to the
        server, which have been observed on some configurations,
	especially VLB 5426 and 5434 with a fast CPU. Note that this
	option results in reduced performance.
<tag>
chipset &dquot;clgd54xx&dquot;
</tag>
	Force detection of the given chipset. Useful if you have a supported
        chipset that is not properly detected, or if you have an unsupported
        chip that might be compatible with a supported one.
<tag>
videoram 1024 (or another value)
</tag>
	This option will override the detected amount of video memory, and
        pretend the given amount of memory is present on the card. This is
        useful on cards with 2Mbyte of memory whose DRAM configuration is
        not compatible with the way the driver enables the upper megabyte of
        memory, or if the memory detection goes wrong. It must be specified
	in the Device section.
<tag>
Option &dquot;fifo_conservative&dquot; (5424/6/8/9/30)
</tag>
	This option will set the CRT FIFO threshold to a conservative value
	for high dot clocks (&gt;= 65 MHz), reducing performance but hopefully
	alleviating problems with `streaks' on the screen (especially when
	a BitBLT operation is in progress).
<tag>
Option &dquot;fifo_aggressive&dquot; (5424/6/8/9/30)
</tag>
	This option will set the CRT FIFO threshold to an aggressive value;
	it will be the same as that used for lower dot clocks. It improves
	performance at high dot clocks.
<tag>
Option &dquot;no_2mb_banksel&dquot; (542x)
</tag>
	This option will cause the driver not to set the `DRAM bank select'
	bit to enable the upper megabyte of memory on a 2Mbyte card. This
	should be helpful with cards equipped with 512Kx8 DRAMs, as opposed
	to 256Kx4/16 DRAMs, when using a virtual screen configuration that
	uses more than 1Mbyte of memory.
<tag>
Option &dquot;probe_clocks&dquot;
</tag>
	This option will force probing of dot clocks on the card. This
        should not be necessary, since the clocks are fixed and the same for
        all Cirrus chipsets. However, they do depend on the motherboard
        supplying a proper standard 14.31818 MHz frequency on the bus. There
        may be ill-designed VLB motherboards that do not supply this
        frequency correctly for certain bus speeds (e.g. scaled up from 33
        MHz). If in doubt, use this option and run `<tt>X -probeonly</tt>'.
	If the
        clocks are very different from the correct clocks shown below, you
        can try a <tt>Clocks</tt> line in the <tt>XF86Config</tt>
	with your deviating clocks.
        In this situation, the MCLK is probably also screwed.

	Correct clocks:
<verb>
	25.2  28.3  41.1  36.1  31.5  40.0  45.1  49.9
	65.0  72.2  75.0  80.0  85.2
</verb>
<tag>
Clockchip &dquot;cirrus&dquot;
</tag>
	This enables programmable clocks. It must be specified in the
	Device section. With this option, the clocks the modes use will
	be automatically selected. Do not specify any Clocks line. This
	option makes a 12.5 MHz clock possible for a 320x200 Doublescan
	mode. Note that some frequencies may be unstable. Only tried
	and tested frequencies (like the default clocks) are guaranteed
	to be stable.
<tag>
Option &dquot;linear&dquot;
</tag>
	This enables linear addressing, which is the mapping of the entire
        framebuffer to a high address beyond system memory, so that SVGA
        bank switching is not necessary. It enhances performance at 256
        colors, and is currently required for 16bpp and 32bpp. See section 4
        for details.
<tag>
Membase 0x00e00000 (or a different address)
</tag>
	This sets the physical memory base address of the linear
        framebuffer. It must be specified in the Device section. It is
	required for most linear addressing configurations.
<tag>
Option &dquot;favour_bitblt&dquot; (5426)
</tag>
	This option will, when the BitBLT engine is enabled, favour its use
        over framebuffer color expansion functions that are normally faster. 
        This can give a performance improvement on a heavily CPU-loaded
        system (e.g. running gcc and other programs at the same time) in
	certain situations.
<tag>
Option &dquot;mmio&dquot; (543x)
</tag>
	This enables the use of memory-mapped I/O to talk to the BitBLT
        engine on the 543x/5429, which is a bit faster. It also enables
	additional acceleration using memory-mapped I/O.
<tag>
Option &dquot;sw_cursor&dquot; (542x/3x)
</tag>
	This disables use of the hardware cursor provided by the chip. Try
        this if the cursor seems to have problems. In particular, use this
	when using dot clocks greater than 85 MHz on the 5434 since the
	chip doesn't fully support the hardware cursor at those clocks.
<tag>
Option &dquot;clgd6225_lcd&dquot;
</tag>
	Provides a work-around for problems on the LCD screen of some
	62x5 laptop chipsets with maximum white colors.
</descrip>


<sect> Mode issues <p>

The accelerated 256-color driver uses 256 bytes of scratch space in video
memory, and the hardware cursor also uses 1K. Consequently, a 1024x1024
virtual resolution should not be used with a 1Mbyte card.

The use of a higher dot clock frequencies has a negative effect on
the performance of graphics operations, especially BitBlt, when little DRAM
bandwidth is left for drawing (the amount is displayed during start-up).
With default MCLK setting (0x1c) and a 32-bit memory interface, performance
with a 65 MHz dot clock can be half of that with a dot clock of 25 MHz.
So if you are short on DRAM bandwidth and experience blitting slowness,
try using the lowest dot clock that is acceptable; for example, on a 14" or
15" screen 800x600 with high refresh (50 MHz dot clock) is not so bad, with
a large virtual screen.

It does not make much sense performance-wise
to use the highest clock (85 MHz) for 1024x768
at 76 Hz on a 542x; the card will almost come to a standstill. A 75 MHz dot
clock results in 70 Hz which should be acceptable. If you have a monitor
that supports 1024x768 at 76 Hz with a 85 MHz dot clock, a standard
5426/5428 based card is a poor match anyway.

5434-based cards with 2Mbyte of memory do much better at high dot clocks;
the DRAM bandwidth is basically double that of the 542x series. The 543x
chips also make more efficient use of the available DRAM bandwidth.

<sect> Linear addressing and 16bpp/32bpp modes <p>

Currently the unaccelerated 16-bit and 32-bit pixel support in the SVGA
server requires linear addressing. This restriction will hopefully be
removed in a future version. Option "linear" can be specified in a
depth-specific screen section to enable linear addressing; a MemBase
setting (in the device section) is probably also required. There
are a number of different card configurations.

If you have a 542x/543x on the ISA bus, and you have 16Mb or more of
system memory, linear addressing is impossible. 16bpp is out, sorry.
If you have less than 14Mb of memory, you may be able to map the
framebuffer at 14Mb, using `<tt>MemBase 0x00e00000</tt>'. That's five zeros
after the `e'. Unfortunately many ISA cards don't support linear
addressing.

If you have a 5424/26/28/29 on VESA local bus, the situation is more
complicated. There are two different types of cards w.r.t. linear
addressing:
<itemize>
<item> Cards that can only map in the lower 16Mb, like cards on the ISA bus.
  This is the case with most cards. The same
  restrictions apply (i.e. you must have less than 16Mb of memory).
<item> Cards that connect address line A26 and always map at 64Mb + 14Mb. In
  this case specify `<tt>MemBase 0x04e00000</tt>'. This assumes you have a
  VLB
  motherboard implementation that implements A26. This has not been tested;
  it is not quite clear whether it maps at 0x04000000 or 0x04e00000.
</itemize>
You will probably have to rely on trial and error. If you have less
than 16Mb memory, the `wrong' membase setting will result in no graphics
being displayed, but you can probably exit with ctrl-alt-backspace.

If you have &gt;= 16Mb memory, the first type of card (and even the second
type with a stupid VLB motherboard) will result in a crash (probably a
spontaneous hard reboot).

It may be possible to find out the type by visual inspection. If the card
has a pin at A26, it is likely to map beyond 64Mb. To do this, take the card
out. At the VESA local bus pins (this is the smaller strip of connector pins
at the non-slot side of the card), consider the right side (this is the side
of the board where all the chips are mounted). There are 45 pins here. They
are numbered 1 to 45, from the inside (i.e. the one nearest to the card end
is 45). Counting from the inside, the 17th pin is probably not present, then
there are pins at 18-20. The 21st is A30, the 22nd is A28 and the 23rd is
A26. So, if we have no pins at at 21-23, the card doesn't map beyond 64Mb. If
there's only a gap of two pins at 21 and 22 (or they are both present) and
there's a pin at 23, the card does probably map beyond 64Mb. If there's a
little logic near that pin on the card, it's more likely.

With a 543x on the local bus things are simpler (the Cirrus Logic windows
drivers use it), but it is not quite without problems.

With a card on the PCI bus, there is a PCI configuration register that holds
the framebuffer base address. However, the driver currently does not read it
out yet, so you'll have to specify the address with MemBase. On one system
tested, it mapped at 0xa0000000, and it appeared addresses where assigned
in 0x08000000 increments over the PCI devices. A program is most likely
available to read out the PCI configuration.

On the VESA local bus, most 543x cards have a default mapping address of
64Mb, with jumper options for 2048Mb and 32Mb. This is probably described in
the documentation that came with the card, or look in the MS-Windows system.ini
file (something with linearaddr = &lt;offset in megabytes&gt;). These different
settings were added by Cirrus Logic after finding that many VLB motherboard
implementations don't implement different address pins (however, they failed
to handle this smoothly in their initial Windows drivers). The driver assumes
a default of 64Mb if MemBase isn't specified. A few examples for MemBase:
<tscreen><verb>
	MemBase	0x02000000	32Mb
	MemBase	0x04000000	64Mb
	MemBase	0x80000000	2048Mb
</verb></tscreen>
The 16bpp and 32bpp modes have limited acceleration (scroll, text)
which means they can be slow, although a good local bus host
interface (like the 543x has) helps a lot. Note that the standard cfb
framebuffer code can be very slow for monochrome stipples and bitmaps.
32bpp mode is only supported on a 5434 with 2Mb or more of memory.

In the <tt>XF86Config</tt> <tt>"Screen"</tt> section, a
<tt>"Display"</tt> subsection must be
defined for each depth that you want to run, with separates Modes
and virtual screen size. Example (2Mb of video memory):
<tscreen><verb>
Section "screen"
    SubSection "Display"
	Depth 8
	Virtual 1152 900
	ViewPort 0 0
	Modes "640x480" "800x600" "1024x768"
	Option "linear"
    EndSubSection
    SubSection "Display"
	Depth 16
	Virtual 1152 900
	ViewPort 0 0
	Modes "640x480" "800x600" "1024x768"
	Option "linear"
    EndSubSection
    SubSection "Display"
	Depth 32
	Virtual 800 600
	ViewPort 0 0
	Modes "640x480" "800x600"
	Option "linear"
    EndSubSection
EndSection
</verb></tscreen>

<sect> The ``cl64xx'' Driver<label id="cl64xx"><p>
The cl64xx driver supports the cl-gd6440 found in many laptops.  For
example, Nan Tan Computer's NP9200, NP3600, etc., which are OEM-ed by
Sager, ProStar, etc. and Texas Instruments TI4000 series are supported.

The driver works in LCD-only, CRT-only, and the chip's SimulScan mode
which allows one to use both the LCD and external CRT displays
simultaneously.  The LCD and Simulscan modes' resolution is 640x480
while, for CRT-only, the standard VESA modes of 640x480, 600x800, and
1024x768 have been tested.  Interlaced 1024x768 mode has never been
debugged and does not work on the machines tested.

The chip has a documented maximum operating limit for its dot clock
that is related to its core voltage.  Specifically, for 5.0V the
maximum dot clock is 65MHz and for 3.3V the maximum dot clock is
40MHz.  The driver checks the core voltage and limits the maximum dot
clock to the corresponding value.  This translates to a maximum  
resolution of about 1024x768 at a 60Hz refresh rate.  The internal 
frequency generator can be programmed higher than these limits and is
done so during server startup when the clocks are probed which
momentarily exceeding the chip's operating limit.  Once a set of valid
clocks is obtained, I would recommend using Clocks lines in
<tt>XF86Config</tt>.  Doing so will also decrease startup time significantly.
The clocks may be obtained by running the X server -probeonly (see the
XFree86 man page for more information about -probeonly).

The data book indicates that only a configuration of one megabyte of
video memory is supported by the chip.  This size has been directly set
in the driver.  If one finds a need, one should be able to override the
default size in <tt>XF86Config</tt>.  Also, with 1MB of video memory, one should
be able to have a virtual screen size of e.g. 1024x1024 and this is  
possible in CRT-only screen mode.  However, whenever the LCD is in use
(LCD and SimulScan), the chip uses a portion of upper video ram for
its own internal acceleration purposes.  Thus, the maximum video memory
available for virtual resolution in LCD modes is about 0.75MB e.g.
1024x768.  If you set the virtual resolution above this, you will see
what might be described as a compressed aliased band when the
accelerated area is displayed.

Currently, the driver does not support switching of screen modes among
LCD, CRT, and SimulScan, and, at least on the NP9200, the mode must be
chosen at OS boot time (e.g. Linux's LILO) while the BIOS is still
active.  It should be possible to add screen mode type selection as a 
ModeLine flag option in <tt>XF86Config</tt> to allow for dynamic screen mode
selection from within the X server.  Finally, the driver does not currently
support any of the powerdown saving features of the chip nor does it  
shut off the LCD's backlight on screen blank.  I hope to implement all
these features in future releases.

The primary contact for the cl6440 problems with ``cl64xx'' driver is
Randy Hendry <em>&lt;randy@sgi.com&gt;</em>.

<sect> Trouble shooting with the ``cirrus'' driver<p>
First of all, make sure that the default modes selected from your
<tt>XF86Config</tt>
is supported by your monitor, i.e. make sure the horizontal sync limit is
correct. It is best to start with standard 640x480x256 with a 25.175 MHz
clock (by specifying a single horizontal sync of 31.5) to make sure the
driver works on your configuration. The default mode used will always be
the first mode listed in the modes line, with the highest dot clock listed
for that resolution in the timing section.

Note that some VESA standard mode timings may give problems on some monitors
(try increasing the horizontal sync pulse, i.e. the difference between
the middle two horizontal timing values).
<descrip>
<tag>There is a video signal, but the screen doesn't sync.</tag>
	You are using a mode that your monitor cannot handle. If it is
	a non-standard mode, maybe you need to tweak the timings a bit. If
	it is a standard mode and frequency that your monitor should be able
	to handle, try to find different timings for a similar mode and
	frequency combination.
<tag>Sparklies/streaks at high dot clocks.</tag>
	You can try the <tt>"fast_dram"</tt> option, or use a lower dot clock.
	If it happens when moving something on the screen, try the
	<tt>"fifo_conservative"</tt> option. If that is not sufficient, the
	<tt>"noaccel"</tt> option or <tt>"no_bitblt"</tt> will probably
	help.
<tag>`Wavy' screen, horizontal jitter.</tag>
	You are probably using a dot clock that is too high; it is also
	possible that there is interference with a close MCLK. Try a
	lower dot clock. You can also try to tweak the mode timings; try
	increasing the second horizontal value somewhat. Here's a 65 MHz
	dot clock 1024x768 mode (about 60 Hz) that might help:
<verb>
 "1024x768"     65      1024 1116 1228 1328     768  783  789  818
</verb>
	If you are using programmable clocks with Clockchip <tt>"cirrus"</tt>,
	try disabling it and using the default set of clocks.
<tag>Crash or hang after start-up (probably with a black screen).</tag>
	Try the <tt>"noaccel"</tt> option. If that works,
	try Option <tt>"no_bitblt"</tt> for
	somewhat better performance. Check that the BIOS settings are OK;
	in particular, disable caching of 0xa0000-0xaffff. Disabling hidden
	DRAM refresh may also help.
<tag>
Crash, hang, or trash on the screen after a graphics operation.
</tag>
	This may be related to a bug in one of the accelerated functions, or
	a problem with the BitBLT engine. Try the <tt>"noaccel"</tt> option,
	or the <tt>"no_bitblt"</tt> option. Also check the BIOS settings.
<tag>
`Blitter timeout' messages from the server.
</tag>
	Same as for the above entry.
<tag>
Screen is `wrapped' vertically.
</tag>
	This indicates a DRAM configuration problem. If your card has two
	megabytes of memory, try the <tt>"no_2mb_banksel"</tt> option, or use
	<tt>videoram "1024"</tt> if you only use 1 Mbyte for the virtual
	screen.
<tag>
Corrupted text in terminal window.
</tag>

	This has been reported on non-standard video implementations.
	Use the <tt>"no_bitblt"</tt> option.
<tag>
Streaks or hangs with laptop chipset
</tag>
	This can happen if the dot clock is high enough to leave very
	little bandwidth for drawing (e.g. 40 MHz on a 512K card), and
	(5422-style) acceleration is used.
<tag>
Occasional erroneous pixels in text, pixel dust when moving window-frame
</tag>	
	Probably related to MCLK setting that is too high (can happen
	with linear addressing even though banked mode runs OK).
<tag>
Chipset is not detected.
</tag>
	Try forcing the chipset to a type that is most similar to what
	you have.
<tag>
Incorrect little lines (mostly white) appear occasionally
</tag>
	This may be related to a problem with system-to-video-memory BitBLT
	operations. Try the <tt>"no_imageblt"</tt> option if it annoys you.
<tag>
Textmode is not properly restored
</tag>
	This has been reported on some configurations. In XFree86 3.1
	the SVGA server probe would corrupt a register on the 543x,
	requiring Chipset line. Normally you should be able to restore
	the textmode font using a utility that sets it (<tt>setfont</tt>,
	<tt>runx</tt>, <tt>restorefont</tt> on Linux).
<tag>
Erratic system behaviour at very high dot clocks
</tag>
	It is possible that high dot clocks on the video card interfere with
	other components in the system (e.g. disk I/O), because of a bad
	card and/or motherboard design. It has been observed on some PCI
	5428-based cards (which are very rare, since the 5428 doesn't
	support PCI).
</descrip>
For other screen drawing related problems, try the <tt>"noaccel"</tt>
option (if <tt>"no_bitblt"</tt> doesn't help).

If are having driver-related problems that are not addressed by this document,
or if you have found bugs in accelerated functions, you can try contacting
the XFree86 team (the current driver maintainer can be reached at
<it>hhanemaa@cs.ruu.nl</it>), or post in the Usenet newsgroup
"<it>comp.windows.x.i386unix</it>".

<sect> Driver Changes <p>
Bugs fixed since XFree86 3.1:
<itemize>
<item>	  Accelerated 14-pixel wide font drawing bug.
<item>	  Server crash when switched to another VC with linear addressing
	  enabled at 8bpp.
<item>	  DAC programming lock-up at VC switch at 16bpp on a 542x.
<item>	  Driver undoes SVGA probe corruption to 543x register.
<item>	  Linear addressing on a 543x with 8bpp (may have caused grief when
          trying to configure 16/32bpp).
<item>	  Hardware cursor color mapping at 16/32bpp.
</itemize>

New features in XFree86 3.1.1:
<itemize>
<item>	  Some speed improvements.
<item>	  Scrolling/text/fill acceleration at 16/32bpp.
<item>	  Support for programmable clocks.
<item>	  Support for Memory-Mapped I/O on 543x.
<item>    Support for dot clocks up to 110 MHz on the 5434.
<item>    Support for the CL6440 in the ``cl64xx'' driver.
</itemize>

<verb>
$XConsortium: cirrus.sgml,v 1.4 95/01/27 16:14:36 kaleb Exp $
$XFree86: xc/programs/Xserver/hw/xfree86/doc/sgml/cirrus.sgml,v 3.8 1995/01/27 04:51:53 dawes Exp $
</verb>

</article>

