I haven't followed this thread as much as I should/would have wanted to so pardon my ignorance, but wouldn't it be possible to design a small daughterboard with a SOIC attiny85 and a 32.768kHz crystal?
A bit like this:
If all we need is to remove the 10/33pF cap, it's not too much of a problem? Again, I haven't taken a good look at the schematics yet so I may be talking nonsense.
It's been a very long time, but ISTR my TrueVision card w/Xilinx on board came up from DeclROM as a startup screen without a driver, but that's NuBus? Dunno, given built-in monitors, maybe some SE/30 PDS VidCards weren't designed to Apple's spec?
Thank you for taking the time to summarize these findings, the knowledge is invaluable for anyone wanting to tinker and explore an old classic. I look forward to the new topic that you plan on posting sometime in the future. Thank you, much obliged.
I don't know about converting video formats but will mention that some of the video cards use Xilinx FPGAs which are configured by their driver. In other words the FPGA doesn't know what it's doing logically, until the driver loads and downloads a bit stream to the FPGA on the video card.
Yeah, if the AVR internally generated RC oscillator is at least as good as Raspberry Pi's small, 19.2MHz crystal, you can easily get ahead/behind by 15 minutes a month, versus 1 minute a month or less with a good stable 32.768kHz crystal. With NTP time sync, you really don't notice, but if you want good old retro time keeping, a design without a good 32.768kHz crystal in the loop leaves much to be wished for.
Also, another note I should point out, the internal load capacitance of the ATTiny85 when using a 32.768kHz crystal for the system clock invalidates the external capacitor selection of 10pF and 33pF, so the crystal connection cannot be used as a drop-in replacement also for this reason.