[PATCH] i2c: omap: improve duty cycle on SCL
ml.lawnick at gmx.de
Wed Jun 17 04:09:53 PDT 2015
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?
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