At the 2013 MSX fair in Nijmegen some of the openMSX members took some measurements of a V9938 using a logic analyzer. After analyzing this data, they figured out when exactly the VDP reads or writes VRAM for which purpose.
This should allow to greatly improve the accuracy of the VDP emulation in openMSX. The work on the emulation part is ongoing (but early results look promising). Meanwhile they've written a document describing these findings in detail. This information may be useful for other MSX emulator developers or for MSX developers in general who like to understand the VDP at a deeper level.
Relevant link: VDP VRAM Timing
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