On Mon, Jan 04, 2021 at 05:43:13PM +0100, groepaz_at_gmx.net wrote: > Am Montag, 4. Januar 2021, 17:19:04 CET schrieb Segher Boessenkool: > > On Sun, Jan 03, 2021 at 09:45:39PM +0100, groepaz_at_gmx.net wrote: > > > Not every detail in the design is clocked, some delays just happen because > > > of gate propagation delays - and when the process changes, those delays > > > may change as well. > > > > Yup, exactly. > > > > > The well known "grey dot" the new VICII produces are related > > > to exactly the same thing. > > > > But this isn't true at all. You get the grey dot if *external* timing > > is off! The difference isn't between VIC-II versions, the difference is > > between boards (and what PLA or PLA replacement is used on that). > > ehrm, no. what you mean is the "sparkle bug" that appeared on very early > boards, that is a totally different thing. > > the "grey dot" only shows on "new" VICII when any color register is being > written, and is clearly related to internal timing. (the color coming from the > pixel pipeline is not valid yet, and the VICII produces "0x0f" color for a > fraction of a pixel). No, this is exactly what I am talking about. You get it because an internal bus still holds the precharged value (which causes the light grey: all ones). On older systems this did not happen. It can be "fixed" by adding a small cap to the #CS line. http://segher.wiibrew.org/c64/plots/vic.html You are right that this is Yet Another example of race conditions. But this one is *not* exposed by the new chip, by new external circuitry instead :-) SegherReceived on 2021-01-04 19:00:02
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