[PATCH] i2c: omap: improve duty cycle on SCL
Felipe Balbi
balbi at ti.com
Wed Jun 17 08:38:12 PDT 2015
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
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