On Thu, Oct 13, 2016 at 07:03:30PM +0100, smf wrote: >I thought upper/lower border was always fetching $3fff? Yes, for the 40 cycles that would within the horizontal borders. Similarly, if the screen is blanked by clearing bit 4 of $d011, each raster line would be like that. >During the side borders it's fetching sprites, so you can't rely on >that for refreshing The 5 refresh cycles are at the left border, immediately followed by the 40 columns. The VIC-Artcle.gz at http://www.zimmers.net/anonftp/pub/cbm/documents/chipdata/ (published 20 years ago) includes some timing diagrams. >I doubt they thought they'd better put a separate dram refresh in case >someone figures out how to mess up the character fetching (duplicating >rows/vsp etc). > >There must be another reason. Remember that the C64 KERNAL blanks the screen during tape access. I think that it is possible that the memory accesses of the KERNAL tape routines would not guarantee sufficient DRAM refresh. Marko Message was sent through the cbm-hackers mailing listReceived on 2016-10-13 20:00:02
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