Re: [PATCH] i2c: omap: improve duty cycle on SCL

[Felipe Balbi <balbi-l0cyMroinI0@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 --]