Re: CIA old/new?

> On 2021-01-07, at 19:30, Segher Boessenkool <segher_at_kernel.crashing.org> wrote:
> 
>> As I mentioned already in this thread - only (some) of the HMOS-II chips expose the problem.
> 
> And yet, everything that matters on those chips is identical, and timing
> difference on the chip (different process) cannot be anywhere near 40ns
> (half a dot clock is 60ns!)

I am not sure I understand you. IF everything that matters was identical, we wouldn't see the difference, would we? If we exclude on-chip propagation times then there has to be something else that "matters" because with the same external timing, still only (some) HMOS-II chips expose the problem.

>> Among those which do, it may depend on the chip's temperature (problem fades with temperature rising). OTOH no single NMOS based VIC expose the issue even with the same board timing. Yes, you can patch the _CS line with a cap and crudely work the problem around this way
> 
> Which I said is not a good solution, only a simple way to show the
> origin of the problem.

Again I am unsure I understand. How do you define "origin" of the problem? Did you conclude that the board's timing is the "origin"?If yes, then after testing lots of combinations my opinion is that the "origin" of the problem lies in the chip. And I give my reasoning.

>> but I say it once again: with the very same _CS timing no NMOS VIC produces the annoying sparkles. So it is up to whoever reads this to decide whether this is a bug of the board/PLA/replacement or the actual HMOS-II VIC. For me it's the latter.
> 
> My position is it is not a bug at all, it is as designed.  And it
> wouldn't even be noticed until very many years later :-)

That "many years later" boil down to actually a few weeks after the narrow boards started to ship in quantities - people quickly started to ask to "fix" their computers. Mostly due to the "faulty" SID, which "couldn't play samples" but also due to the sparkles on the screen. Back then the only thing I could tell them was "if that annoys you - get an older model". I didn't know I could put a cap to make them happy ;-)

-- 
SD!