Re: Re: CIA old/new?

This has been tested to fix the issue with a cap on the CS line? I'll have to try it. 
It seems like I've put HMOS VIC-II into an older board (fixing the voltage issue) and it had the dots, but that may not matter, as you mentioned.
I assume this is the line that goes from CS to the "VIC" pin on the new PLA on a 250469? Trace cut and put cap between them?
-Pete
On Mon, Jan 4, 2021 at 12:23 PM, Segher Boessenkool  wrote:
On Mon, Jan 04, 2021 at 05:43:13PM +0100, groepaz_at_gmx.net (mailto: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 (mailto:groepaz@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 (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 :-)

Segher