From: Michael Lawnick <ml.lawnick@gmx.de>
To: Felipe Balbi <balbi@ti.com>, wsa@the-dreams.de
Cc: Tony Lindgren <tony@atomide.com>, Nishanth Menon <nm@ti.com>,
Dave Gerlach <d-gerlach@ti.com>,
linux-i2c@vger.kernel.org,
Linux OMAP Mailing List <linux-omap@vger.kernel.org>,
Linux ARM Kernel Mailing List
<linux-arm-kernel@lists.infradead.org>
Subject: Re: [PATCH] i2c: omap: improve duty cycle on SCL
Date: Wed, 17 Jun 2015 13:09:53 +0200 [thread overview]
Message-ID: <55815581.80807@gmx.de> (raw)
In-Reply-To: <1434482276-1210-1-git-send-email-balbi@ti.com>
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?
--
KR
Michael
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WARNING: multiple messages have this Message-ID (diff)
From: ml.lawnick@gmx.de (Michael Lawnick)
To: linux-arm-kernel@lists.infradead.org
Subject: [PATCH] i2c: omap: improve duty cycle on SCL
Date: Wed, 17 Jun 2015 13:09:53 +0200 [thread overview]
Message-ID: <55815581.80807@gmx.de> (raw)
In-Reply-To: <1434482276-1210-1-git-send-email-balbi@ti.com>
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?
--
KR
Michael
next prev parent reply other threads:[~2015-06-17 11:09 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 [this message]
2015-06-17 11:09 ` Michael Lawnick
[not found] ` <55815581.80807-Mmb7MZpHnFY@public.gmane.org>
2015-06-17 15:38 ` Felipe Balbi
2015-06-17 15:38 ` Felipe Balbi
[not found] ` <20150617153812.GB18421-HgARHv6XitJaoMGHk7MhZQC/G2K4zDHf@public.gmane.org>
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
[not found] ` <20150618172428.GB27790-HgARHv6XitJaoMGHk7MhZQC/G2K4zDHf@public.gmane.org>
2015-06-19 5:41 ` Michael Lawnick
2015-06-19 5:41 ` Michael Lawnick
[not found] ` <5583AB9D.6090805-Mmb7MZpHnFY@public.gmane.org>
2015-06-19 15:30 ` Felipe Balbi
2015-06-19 15:30 ` Felipe Balbi
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