pjw wrote: Are HDMI and USB (as on the RasPI) very much harder to implement? I know its chasing a fast-moving target, but going for these later standards would give your design an extra 5-10 years of life?
The first Q68 hardware was designed over 8 years ago. So if I started today, I might use a newer component here or there, but still not add USB hardware.
Why? Because the basic idea of the Q68 is to be a strictly native hardware, with 68K CPU, no emulation at all !
That's what differs from emulation under ARM Linux like Raspberry, even from FPGA boards running (limited) USB support on a second processor. The basic idea of the Q68 requires that all hardware must be supported by QL drivers. As Tobias explained, this makes USB unrealistic.
HDMI doesn't contradict the "strictly native hardware" approach, but it tends to make things expensive and harder to build. And there is an additional point: For being the only
video output, HDMI might still be "too new". For example, my existing monitors for retro computing are still in 4:3 format and have VGA! I would end up converting HDMI back to VGA by an external converter.
It seems easier to go the opposite way and use mass market VGA-to-HDMI converters, in case the monitor no longer has VGA input. The Q68 has at least VESA standard 1024x768, which is so widespread that every converter should be able to deal with it.
As a last resort, in case PS/2 dies, we could still go "non-native" and tinker a little co-processor board with USB that connects to the Q68 expansion bus. But not now.