Peter wrote:Back to your older post:
What I tried to say: There are cheap variants of SD card that you can solder also - you don't need serial flash for that. In case of the Q68, the loaded "ROM" is booted by a true hardware reset after it is in memory, so I don't see what to win by serial flash. (Of course, the loader screen output could be removed just in case someone wants to load his own loader first.) Using SD card saves pins in case of double usage for removable storage.
Ah - well, I was thinking about it in terms of a more general purpose CPU, not necessarily a QL thing. Reason I mentioned it was because QSPI is VERY similar to SD so implementation would be similar and in case SD was provided too, probably pins would be shared too. QSPI is indeed I think a development of uSD, it is even simpler to use, but for our purposes if one can reliably solder in a SD card as a 'fixed storage' that can be re-programmed, of course there would not be any sense in having it if there are already all the necessary SD hardware and software resources.
Nasta wrote:TBH I would leave microdrive access to classic QLs.
We already have a non-classic version, which is the Q68. A SGC replacement would be especially for the original QL case
... hard to estimate how many of those
users would like to keep a microdrive. My guess is 30..40% including myself. What would you guess?
Probably less, since it's predecessors already had floppy interfaces and were around for... well, decades (almost can't believe it's been that long!).
Even then I think it became a sort of unspoken concensus that MDV contents should be transferred to other more reliable media.
However, I may be writing based on a wrong assumption - that is, the replacement replaces the whole motherboard.
If the SGC replacement indeed is a functional replacement plus graphics, then it would plug into a J1 connector on a QL motherboard, which means even if 8301 video is not used, 8302 and IPC are still available? Maybe I was confused by the mention of matrix keyboard hardware - would it not be included in this case, via IPC? And microdrives would of course be available through the 8302.
Nasta wrote:So, if I can make a wish, it would be for a multiplexed (reduced pin count) real 16-bit expansion bus - based on the existing pin count for the non-multiplexed version. Even if not all of the 16 bits available during the 'address phase' on the bus are not used as an address, it would open up a lot of possibility for future expansion.
I consider that. The existing bus lacks one pin for the "address latch enable", if the non-multiplexed 8 bit mode is also kept. So I need to work out a specialty. For example using chip select as an inverted address latch enable.
Hmmm, now again I am confused - are we talking about the Q68 or a hypothetical SGC replacement, based on Q68 technology?
If Q68, is there any actual hardware that uses the expansion port on it, or in a stage of design and manufacture that it is too late too change the bus spec and implementation (assumption here is that the FPGA could be reprogrammed on existing Q68 so the expansion port becomes multiplexed 16 bit)?
8-bit access so far (as far as I understand) was actually half-word access so no need to re-implement that, 8-bit data would still go to half of a 16-bit word. This is the case I was making a wish for, I wish I had known of how it was specified before the documentation became available, I would have started a campaign for a multiplexed 16 bit bus early
If SGC successor, then real 8-bit access (real address A0) has to be implemented or existing code to access 8302/IPC will not function, OR, 'half-word' access can be used but then code has to be modified to reflect the fact that previously successive byte addresses now appear as 'stretched out' to only even bytes. Re-mapping the Q68 IO area (assuming the Q68 design is used as a template for the SGC successor) to Q68 Io area is a minor issue, easily solved.
Or am I missing something?
At this point I guess I need to ask for more detail on the hardware that is being proposed for the Q68 based SGC successor?