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@@ -0,0 +1,59 @@ + +MediaGX Fun +----------- + +This tries to document the "gotcha's" associated with the Cyrix +hardware and also the SoftVGA (SMM BIOS emulation of video) implementation. + +o Palette Handling + + In theory 8bit modes can use the VGA colour control. In practice + this doesn't work at least on some 5530 based systems with LCD + displays. + + Some 5510 based systems need special handling for external LCD + RAMDAC. We don't currently do this. + +o Mode Switches + + If you load unsuitable data into the Soft VGA mode switching + registers or forgot to set the ModeSwitch disable before you + load the registers up mode switches may fail. In a few cases + you get bogus illegal instructions reported + +o BIOS Versions + + The VSA1/VSA2 firmware that does all the magic on the Cyrix + processors is an SMM mode software block in the BIOS. This means + the Cyrix is one system where different BIOSes have different bugs + instead of just having to fight the hardware + + The BIOS is just plain unusable in a few systems. Code exists to + do some mode switches the hard way without VSA getting involved. + +o Compression Buffer + + To cut down on the memory usage the display scan checks dirty + bits on each scan line (per frame in some situations) and if the + line is dirty it scans it from the original buffer and writes back + a compressed line if it can do so. If it does this it clears the + dirty bit. We have to handle dirty bits ourselves and getting it + wrong produces interesting visuals. + +o Memory Layout + + When you use VSA to do mode set up it makes certain assumptions + about memory layout. Typically it lays out the frame buffer + with the compression buffer at the end. When there is enough + space between the lines (the chip only handles 1024/2048 bytes + stride) it will hide them in the gaps + + + +To Do +----- +- Add bare-metal setup option for the BIOS afflicted +- Add 5510 external ics5432 RAMDAC support +- Restore hardware cursor support +- DDC/EDID and friends +- RandR would be nice for the tablet pc systems |