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!
