Reply 60 of 178, by mkarcher
feipoa wrote on 2023-09-30, 12:24:
The screen still jitters at 1280x1024x256c at 60 Hz, but it jitters in a different manner compared to how the non-edited BIOS was jittering.
The "60Hz jitter" looks like an issue with the memory clock. Either the memory clock is too high for the memory chips, so they can't provide data fast enough, or the memory clock is too low for 1280x1024x256c at 60Hz, so the card gets "buffer underruns" on the video memory FIFO all the time. I told you to patch the part of the BIOS code that inhibits the 60 Hz mode is the BIOS is not configured for a 110MHz DAC, which obviously worked as intended. If I didn't miss anything while re-checking the BIOS code, the BIOS does not do anything about programming MCLK, but MCLK is selected by extenally choosing a clock on the clock chip. You might need to increase the memory clock by re-configuring the clock chip to get sufficient bandwidth.