Re: Debugging i2c : i2cdetect cant detect a device on i2c line
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. -- RMK's Patch system: https://www.armlinux.org.uk/developer/patches/ FTTP is here! 80Mbps down 10Mbps up. Decent connectivity at last!
On Thu, 7 Sept 2023, 14:56 Russell King (Oracle), <linux@armlinux.org.uk> 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? --
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@kernelnewbies.org https://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
On Thu, Sep 7, 2023 at 9:47 PM Lucas Tanure <tanure@linux.com> wrote:
On Thu, 7 Sept 2023, 14:56 Russell King (Oracle), <linux@armlinux.org.uk> 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.
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.
-- 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@kernelnewbies.org https://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
On Thu, 7 Sept 2023, 18:08 Raul Piper, <raulpblooper@gmail.com> wrote:
On Thu, Sep 7, 2023 at 9:47 PM Lucas Tanure <tanure@linux.com> wrote:
On Thu, 7 Sept 2023, 14:56 Russell King (Oracle), <linux@armlinux.org.uk>
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.
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 lines. 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.
-- 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@kernelnewbies.org https://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
On Thu, Sep 07, 2023 at 10:38:10PM +0530, Raul Piper wrote:
On Thu, Sep 7, 2023 at 9:47 PM Lucas Tanure <tanure@linux.com> wrote:
On Thu, 7 Sept 2023, 14:56 Russell King (Oracle), <linux@armlinux.org.uk> 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.
Where can I change this time? Can you please provide example of some device/device tree?
You can't directly. The rise time is a function of the capacitive loading on the lines and the pull-up resistor. It's not a software parameter.
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.
This makes me convinced that you're not familiar with electronics. Vil is a pretty standard parameter in all digital logic for "Voltage, input, low" - the voltage at which it is guaranteed that the device will see a logic 0 signal on its input. If I draw a diagram illustrating the voltage levels on an input, top is the supply voltage, bottom is ground, then most are: +------+ <--- Vcc (supply voltage) | | <--- Within this region, it is guaranteed that | | the device will see a logic 1 +------+ <--- Vih (input high) |//////| |\\\\\\| <--- Within this region, the value that the |//////| device sees is indeterminant |\\\\\\| +------+ <--- Vil (input low) | | | | +------+ <--- Ground (0V) So, if the voltage on the SDA and SCL pins does not reach Vil or below, there is no guarantee that the device will see a logic 0 on its input, and it either won't work, it may sporadically work. Basically, Vil is the threshold voltage at which the manufacturer _guarantees_ that the device will see a logic 0, and Vih is the threshold voltage at which the manufacturer _guarantees_ that the device will see a logic 1. Both these parameters will be specified in the data sheet, possibly as a function of supply voltage.
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.
Which means either the device is not seeing the logic levels necessary to receive the address, or maybe if this is a prototype I2C device, maybe it has a bug in its address matching logic, or the address is incorrectly set. I'd first be checking that the Vih and Vil for this device are being achieved by putting an oscilloscope on its input pin and comparing that with the device specification. -- RMK's Patch system: https://www.armlinux.org.uk/developer/patches/ FTTP is here! 80Mbps down 10Mbps up. Decent connectivity at last!
On Thu, Sep 07, 2023 at 05:17:47PM +0100, Lucas Tanure wrote:
On Thu, 7 Sept 2023, 14:56 Russell King (Oracle), <linux@armlinux.org.uk> 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!
participants (3)
-
Lucas Tanure -
Raul Piper -
Russell King (Oracle)