From: balbi@ti.com (Felipe Balbi)
To: linux-arm-kernel@lists.infradead.org
Subject: [PATCH] i2c: omap: improve duty cycle on SCL
Date: Wed, 17 Jun 2015 10:38:12 -0500 [thread overview]
Message-ID: <20150617153812.GB18421@saruman.tx.rr.com> (raw)
In-Reply-To: <55815581.80807@gmx.de>
Hi,
On Wed, Jun 17, 2015 at 01:09:53PM +0200, Michael Lawnick wrote:
> Am 16.06.2015 um 21:17 schrieb Felipe Balbi:
> >With this patch we try to be as close to 50%
> >duty cycle as possible. The reason for this
> >is that some devices present an erratic behavior
> >with certain duty cycles.
> >
> >One such example is TPS65218 PMIC which fails
> >to change voltages when running @ 400kHz and
> >duty cycle is lower than 34%.
> >
> >The idea of the patch is simple:
> >
> >calculate desired scl_period from requested scl
> >and use 50% for tLow and 50% for tHigh.
> ...
> Hmm, and what's about Philips I2C specification 2.1, Jan 2000, Table 5?
>
> >PARAMETER SYMBOL STANDARD-MODE FAST-MODE UNIT
> > MIN. MAX. MIN. MAX.
> >LOW period of the SCL clock tLOW 4.7 ? 1.3 ? ?s
> >HIGH period of the SCL clock tHIGH 4.0 ? 0.6 ? ?s
>
> Your signal is in spec (0.85 ?s high, 1,65 low).
> Maybe your TPS65218 is just buggy or signals are bad?
yes, tps is buggy, it's written in the commit log itself.
--
balbi
-------------- next part --------------
A non-text attachment was scrubbed...
Name: signature.asc
Type: application/pgp-signature
Size: 819 bytes
Desc: Digital signature
URL: <http://lists.infradead.org/pipermail/linux-arm-kernel/attachments/20150617/0f2305fc/attachment.sig>
WARNING: multiple messages have this Message-ID (diff)
From: Felipe Balbi <balbi-l0cyMroinI0@public.gmane.org>
To: Michael Lawnick <ml.lawnick-Mmb7MZpHnFY@public.gmane.org>
Cc: Felipe Balbi <balbi-l0cyMroinI0@public.gmane.org>,
wsa-z923LK4zBo2bacvFa/9K2g@public.gmane.org,
Tony Lindgren <tony-4v6yS6AI5VpBDgjK7y7TUQ@public.gmane.org>,
Nishanth Menon <nm-l0cyMroinI0@public.gmane.org>,
Dave Gerlach <d-gerlach-l0cyMroinI0@public.gmane.org>,
linux-i2c-u79uwXL29TY76Z2rM5mHXA@public.gmane.org,
Linux OMAP Mailing List
<linux-omap-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>,
Linux ARM Kernel Mailing List
<linux-arm-kernel-IAPFreCvJWM7uuMidbF8XUB+6BGkLq7r@public.gmane.org>
Subject: Re: [PATCH] i2c: omap: improve duty cycle on SCL
Date: Wed, 17 Jun 2015 10:38:12 -0500 [thread overview]
Message-ID: <20150617153812.GB18421@saruman.tx.rr.com> (raw)
In-Reply-To: <55815581.80807-Mmb7MZpHnFY@public.gmane.org>
[-- Attachment #1: Type: text/plain, Size: 1171 bytes --]
Hi,
On Wed, Jun 17, 2015 at 01:09:53PM +0200, Michael Lawnick wrote:
> Am 16.06.2015 um 21:17 schrieb Felipe Balbi:
> >With this patch we try to be as close to 50%
> >duty cycle as possible. The reason for this
> >is that some devices present an erratic behavior
> >with certain duty cycles.
> >
> >One such example is TPS65218 PMIC which fails
> >to change voltages when running @ 400kHz and
> >duty cycle is lower than 34%.
> >
> >The idea of the patch is simple:
> >
> >calculate desired scl_period from requested scl
> >and use 50% for tLow and 50% for tHigh.
> ...
> Hmm, and what's about Philips I2C specification 2.1, Jan 2000, Table 5?
>
> >PARAMETER SYMBOL STANDARD-MODE FAST-MODE UNIT
> > MIN. MAX. MIN. MAX.
> >LOW period of the SCL clock tLOW 4.7 – 1.3 – µs
> >HIGH period of the SCL clock tHIGH 4.0 – 0.6 – µs
>
> Your signal is in spec (0.85 µs high, 1,65 low).
> Maybe your TPS65218 is just buggy or signals are bad?
yes, tps is buggy, it's written in the commit log itself.
--
balbi
[-- Attachment #2: Digital signature --]
[-- Type: application/pgp-signature, Size: 819 bytes --]
next prev parent reply other threads:[~2015-06-17 15:38 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-06-16 19:17 [PATCH] i2c: omap: improve duty cycle on SCL Felipe Balbi
2015-06-16 19:17 ` Felipe Balbi
2015-06-16 19:19 ` Felipe Balbi
2015-06-16 19:19 ` Felipe Balbi
2015-06-17 11:09 ` Michael Lawnick
2015-06-17 11:09 ` Michael Lawnick
2015-06-17 15:38 ` Felipe Balbi [this message]
2015-06-17 15:38 ` Felipe Balbi
2015-06-18 6:39 ` Michael Lawnick
2015-06-18 6:39 ` Michael Lawnick
2015-06-18 17:24 ` Felipe Balbi
2015-06-18 17:24 ` Felipe Balbi
2015-06-19 5:41 ` Michael Lawnick
2015-06-19 5:41 ` Michael Lawnick
2015-06-19 15:30 ` Felipe Balbi
2015-06-19 15:30 ` Felipe Balbi
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20150617153812.GB18421@saruman.tx.rr.com \
--to=balbi@ti.com \
--cc=linux-arm-kernel@lists.infradead.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.