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Date:      Mon, 20 Aug 2018 07:16:15 -0700
From:      Mark Millard <marklmi26-fbsd@yahoo.com>
To:        Daniel Braniss <danny@cs.huji.ac.il>
Cc:        Ian Lepore <ian@freebsd.org>, Rajesh Kumar <rajfbsd@gmail.com>, Toomas Soome via freebsd-hackers <freebsd-hackers@freebsd.org>, freebsd-drivers@freebsd.org
Subject:   Re: Need a clarification regarding I2C bus frequency in FreeBSD
Message-ID:  <35F2C250-B4CB-4C53-BF8F-43C338022E34@yahoo.com>
In-Reply-To: <1534771095.27158.46.camel@freebsd.org>
References:  <CAAO%2BANOXwXAzJt%2BBZez6422jqKjrKPboSe_%2BudnOCWxYqE-=sQ@mail.gmail.com> <1534523216.27158.17.camel@freebsd.org> <CAAO%2BANOs_YVov-d21Em1EHzajQw7wHsxkzZCnsZwkfBr2=mEiA@mail.gmail.com> <1534702861.27158.36.camel@freebsd.org> <BF721728-B6F5-4214-9180-B911D32D9FCA@cs.huji.ac.il> <A8202939-328A-4564-9CF5-F5F66F68B7B0@cs.huji.ac.il> <1534771095.27158.46.camel@freebsd.org>

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On 2018-Aug-20, at 6:18 AM, Ian Lepore <ian at freebsd.org> wrote:

> On Mon, 2018-08-20 at 11:13 +0300, Daniel Braniss wrote:
>>=20
>>>=20
>>> On 20 Aug 2018, at 09:49, Daniel Braniss <danny@cs.huji.ac.il> =
wrote:
>>>=20
>>>> . . .
>>>=20
>>> hi,
>>> I have similar issues with the allwinner/twsi but I do have a Saleae =
Logic and here is a nice picture:
>> ah, maybe this is better:
>> 	=
https://cs.huji.ac.il/~danny/Screen%20Shot%202018-08-20%20at%2011.06.43.pn=
g
> . . .
> This has nothing to do with the twsi driver, this is about the ig4
> driver (found in sys/dev/ichiic).
>=20
> That screenshot seems to show a bus running at 100KHz like it should
> (although the 62:38 duty cycle is a bit suspicious).

Being a logic analyzer display, it my just be that the threshold
was off from the optimal value. The waveform shape is not really
visible.

The logic analyzer output also shows a thick "rising" edge without the
uparrow symbol. My guess would be that is a rising/falling/rising
sequence that on the scale in use does not show space between edges. In
other words: a glitch on the leading edge side of the intended pulse.
This too might be tied to the threshold used vs . the actual signal
properties: no way to tell from what is shown.

=3D=3D=3D
Mark Millard
marklmi at yahoo.com
( dsl-only.net went
away in early 2018-Mar)




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