Re: Debugging i2c : i2cdetect cant detect a device on i2c line

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

 



On Thu, Sep 07, 2023 at 05:17:47PM +0100, Lucas Tanure wrote:
> On Thu, 7 Sept 2023, 14:56 Russell King (Oracle), <linux@xxxxxxxxxxxxxxx>
> wrote:
> 
> > 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 Arm
> > > > 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 time
> > > > , 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
> > success.
> > > > 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 joke.
> >
> > 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.
> >
> > 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.
> >
> > 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.
> >
> 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?

I assume you are replying to Bagas? Please me it clear in future.
Thanks.

-- 
RMK's Patch system: https://www.armlinux.org.uk/developer/patches/
FTTP is here! 80Mbps down 10Mbps up. Decent connectivity at last!

_______________________________________________
Kernelnewbies mailing list
Kernelnewbies@xxxxxxxxxxxxxxxxx
https://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies



[Index of Archives]     [Newbies FAQ]     [Linux Kernel Mentors]     [Linux Kernel Development]     [IETF Annouce]     [Git]     [Networking]     [Security]     [Bugtraq]     [Yosemite]     [MIPS Linux]     [ARM Linux]     [Linux RAID]     [Linux SCSI]     [Linux ACPI]

  Powered by Linux