Messages in this thread | | | Date | Tue, 5 Apr 2022 17:11:18 +0200 | Subject | Re: [PATCH 0/3] Ensure Low period of SCL is correct | From | Neil Armstrong <> |
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Hi,
On 28/03/2022 23:51, Lucas Tanure wrote: > > > On Mon, 28 Mar 2022, 21:37 Kevin Hilman, <khilman@baylibre.com <mailto:khilman@baylibre.com>> wrote: > > Hi Lucas, > > Lucas Tanure <tanure@linux.com <mailto:tanure@linux.com>> writes: > > > The default duty cycle of 33% is less than the required > > by the I2C specs for the LOW period of the SCL clock. > > > > So, for 100Khz or less, use 50%H/50%L duty cycle, and > > for the clock above 100Khz, use 40%H/60%L duty cycle. > > That ensures the low period of SCL is always more than > > the minimum required by the specs at any given frequency. > > Thanks for the fixes! > > This is going to affect all SoCs, so ould you please summarize how your > changes were tested, and on which SoCs & boards? > > Thanks, > > Kevin > > > Hi, > > I only tested against vim3 board, measured the bus with an saleae logic pro 16. > The measurements were with 100k, 400k and a few in between frequencies. > > Is that enough?
I did a few measures on the Libre Computer Le Potato S905X board:
i2c_AO:
Before the patchset, I got: - 100KHz: 1.66uS HIGH, 6.75uS LOW, 20%/80%, Freq 118KHz /!\ - 400KHz: Unable to decode, clock line is invalid, Data line is also invalid
With the patchset - 100KHz: 4.25uS HIGH, 6.58uS LOW, 40%/60%, Freq 92KHz - 400KHz: 0.33uS HIGH, 3.00uS LOW, 10%/90%, Freq 300KHz
i2c_B:
Before the patchset, I got: - 100KHz: 2.25uS HIGH, 5.41uS LOW, 29%/71%, Freq 130KHz /!\ - 400KHz: 0.42uS HIGH, 1.66uS LOW, 20%/80%, Freq 480KHz /!\
With the patchset - 100KHz: 4.75uS HIGH, 5.42uS LOW, 46%/54%, Freq 98KHz - 400KHz: 0.66uS HIGH, 2.00uS LOW, 24%/75%, Freq 375KHz
So this fixes the frequency, before they were invalid. And it fixes 400KHz on i2c_AO...
I do not understand why behavior is different between i2c_AO & i2c_B, they are feed with the same clock so it should be the same.
Did you check on both i2c interfaces ? can you share your results ?
Neil
> > Thanks > Lucas > > >
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