Information for Tseng Chipset Users : linear memory base address (MemBase) issues : Some boards simply cannot work in linear mode
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## 9.6. Some boards simply cannot work in linear mode

Yes, and in that case, you're out of luck.

There can be at least two reasons for this.

The first is the most common: the board manufacturer has left out the necessary connections and hardware to be able to use linear addressing. This means that no coding effort on this planet can help you with your problem: it is physically impossible to use linear addressing.

The second reason is that the current XFree86 Tseng linear addressing code is incompatible with the way your board is designed. The XFree86 Tseng code assumes a 1:1 mapping of the address lines from the bus (either ISA, VLB or PCI) to the address lines on the Tseng VGA chip. As unlikely as it may sound, this may NOT be the case!

Some very rare boards do not have such a 1:1 mapping (e.g. two address lines swapped). It is possible to support this type of hardware, but at this moment, this has not been implemented yet.

Other boards use external address decoding hardware that combines a number of address lines on the bus to a (smaller) number of address lines to the VGA chip. One such board for example uses three NOR gates (one 74F02 chip) to combine the 6 upper address lines to three address pins on the W32i chip. Obviously, this represents a 2:1 mapping, and not a 1:1 mapping. Therefor, this board is not "compatible" with the way XFree86 implements linear mode.

Information for Tseng Chipset Users : linear memory base address (MemBase) issues : Some boards simply cannot work in linear mode
Previous: Restrictions
Next: How can I see if the linear address is wrong?