Debugging i2c : i2cdetect cant detect a device on i2c line
tanure at linux.com
Thu Sep 7 13:23:33 EDT 2023
On Thu, 7 Sept 2023, 18:08 Raul Piper, <raulpblooper at gmail.com> wrote:
> On Thu, Sep 7, 2023 at 9:47 PM Lucas Tanure <tanure at linux.com> wrote:
> > On Thu, 7 Sept 2023, 14:56 Russell King (Oracle), <linux at armlinux.org.uk>
> >> On Thu, Sep 07, 2023 at 08:36:32PM +0700, Bagas Sanjaya wrote:
> >> > [also Cc: devicetree and ARM folks]
> >> >
> >> > On Thu, Sep 07, 2023 at 08:21:44AM +0530, Raul Piper wrote:
> >> > > Hello ,
> >> > > I am trying to detect an i2c device A on i2c1 line on one of the
> >> > > Cortex A7 platform but not able to see any device on a given
> address (
> >> > > 0x3d) .
> >> > >
> >> > > Is there any parameters of i2c which i can change like rise/fall
> >> > > , timeout etc in a device tree or kernel source and re test it?
> >> > > I have tried changing the i2c speed from 100KHz to 400 KHz but no
> >> > > I have even tried removing the 1.5K pull ups on the i2c lines but
> no result.
> >> Honestly, from this description, I'm wondering if this posting is a
> >> I2C is entirely _reliant_ on pull-ups. It's a wire-or bus, and the
> >> logic 1 state is created by no device pulling the signal low, thereby
> >> allowing the pull-up resistor to pull the line to the logic 1 state.
> >> The pull-up must be the correct strength for the devices on the bus.
> >> If it is too strong, then a driver may not be able to pull the signal
> >> sufficiently low for other devices to register it as a logic 0.
> >> Conversely, the pull-up must be strong enough so that the rise-time
> >> of the signal is sufficient to register as a logic 1.
> >> If it's a problem with the rise time, then increasing the clock rate
> >> will just make the situation worse.
> Where can I change this time? Can you please provide example of some
> device/device tree?
> >> So, if other devices work on the bus, it could be that the Vil
> >> threshold of this device is not being achieved, whereas the other
> >> devices are happy. Therefore, I would suggest you study the data
> >> sheets of the device that isn't being detected.
> What Vil threshold? I checked the power supply to this device and it
> is ~3.3 V as expected.
> >> Lastly, if the undetectable device has a reset line, it's possible
> >> that the device isn't responding because it's being held in reset.
> The device is fine, I am sure about it. As the device provides data on
> USART as well and I am getting it.
> > Please try to use an logic analyser like saleae logic.
> > Probe the i2c bus, reset line, power lines, pins that set the i2c
> address for the device.
> > Can tell us which device it is?
> Its a GPS sensor(still under development) .Logic Analyser gives NACK
> on the given address.
> I may be using the wrong pull ups value which i am checking.But from
> software point of view is there a Device tree setting to enable the
> internal pull ups or adjust the rise/fall time as said above.
Read a little about the i2c protocol and check the signal levels of the i2c
In my experience you can understand the problem by just looking at the
signal levels if understand a little bit of i2c protocol.
Use the digital and analogue parts of you logic analyser.
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