ET4000 driver features

Information for Tseng Chipset Users : ET4000 driver features
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## 2. ET4000 driver features

The SVGA driver for ET4000 chipsets supports all color depths (8, 15, 16, 24 and 24 bpp) on most ET4000 chips starting with the ET4000W32i. The ET4000W32 only supports 8bpp. Depending on the RAMDAC and the support code in the SVGA server, some cards may only support a few of these color depths, or even only 8bpp.

On W32p chips all color depths are supported on the supported RAMDACs (currently ICS5341, STG170x and Chrontel CH8398). These modes are also accelerated. On W32i chips, only AT&T49x compatible RAMDACs will support 16 and 24 bpp modes, and there is no acceleration support (yet).

W32p revision a and b chips are limited to 1 MB of video memory in linear memory modes with acceleration (i.e. in 16/24/32 bpp modes). This is a hardware limitation.

Cards with a RAMDAC that is not yet supported will be limited in a similar manner as the older cards, i.e. to a maximum pixel clock of 86 MHz, whilst they actually might be able to go up to 135 MHz. As a result, 1280x1024 modes will only be possible when using interlacing, and non-interlaced modes are limited to about 1024x768 at 75 Hz refresh.

For a non-interlaced 1280x1024x(256 colors) at say 135-MHz, you need a w32p (with its 16-bit RAMDAC bus) with a multiplexing RAMDAC so that the w32p sees only (135/2 = 67.5) MHz, not 135 MHz. This requires special code only provided for cards using the ICS5341 GENDAC or the STG170x. This code seems to work fine for most people, except, with the ICS5341, for a small band of frequencies around 90MHz.

Linear memory mode (especially important for some DGA clients, and required for 16/24/32 bpp modes) is supported on all ET4000W32i and ET4000W32p cards, but not on the ET4000W32. On ET4000W32p revision a and b, linear memory is limited to 1 MB.

For the higher color depths (16, 24 and 32 bpp), linear memory mode is REQUIRED. It is enabled by default in these modes. There is no need to specify that in the `XF86Config` file. Please read the section on linear memory below: it contains some vital information on how to avoid serious problems.

To force linear memory mode at 8bpp modes, put the following in the Device section of your `XF86Config`:

      Option "linear"

Acceleration support is present, and enabled by default, for W32p chips (not yet for W32i, but that's being worked on). This is based on the new XFree86 acceleration interface (XAA). See also README.W32.

If you have problems with acceleration, acceleration can be disabled by putting the following in the Device section of your `XF86Config`:

      Option "noaccel"

On some (fast) systems, acceleration may cause occasional font corruption. Until this problem is fixed, font acceleration may be disabled using the following in the Device section of your `XF86Config`:

      Option "xaa_no_color_exp"

Information for Tseng Chipset Users : ET4000 driver features
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