Mia Magnusson wrote: > That would give 640k, if replacing two banks of 4164 with 4*256'. But > maybe it wouldn't be too much work to add an extra bank of 2*256's? > That would give RAM from 0 to DFFFF. That is actually so much that some > kind of disable logic would be needed if some "real" PC hardware would > be added. Two banks of 256 kB would indeed give 640 kB plus video RAM at segment B000, I think for PC emulation that would be enough. > Is there any use for more memory on the 6509 side? I don't know any CBM-II program that would use it. > Something with REP CMPSB or REP CMPSW might be possible, letting the > CPU do the whole compare in one go. If REP doesn't work the CMPSB and > CMPSW is still of good use as in a normal loop it's easy to insert the > code that handles changed bytes. Judging by the information here: http://www.cs.dartmouth.edu/~mckeeman/cs48/mxcom/doc/x86.html REP CMPSW on the whole screen should take about 12 ms on a 5 MHz 8088. It could be divided into checking 256-character chunks, for example, and updating only those that changed. Then actually encoding these into PETSCII and saving somewhere later would take several times more in the worst case, plus a call to 6509 to copy prepared PETSCII data to the screen. It is lots of time but manageable, especially if we replace the 8088 with a V20 which should be noticeably faster here. Regards, Michau. Message was sent through the cbm-hackers mailing listReceived on 2017-10-19 10:03:32
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