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Last Post 18 Mar 2014 05:58 AM by  Zile
I2C latency on the Torpedo Wireless and Linux
 2 Replies
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Zile
New Member
New Member
Posts:45


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15 Nov 2013 10:47 AM

     

    Hello,

    I have connected battery gauge on the i2c-2 bus of the Torpedo Wireless. I am able to read gauge registers from application with read/write to file or from console with i2cget command, but sometimes I got some kernel warnings like:

    omap_device: omap_i2c.2: new worst case deactivate latency 0: 122070
    user.warn kernel: [  420.015838] omap_device: omap_i2c.2: new worst case deactivate latency 0: 122070

    or,

    omap_device: omap_i2c.2: new worst case activate latency 0: 244140
    user.warn kernel: [  680.015106] omap_device: omap_i2c.2: new worst case activate latency 0: 244140

    And "new worst case (de)activate latency" each time got higher value.

    It seems like that Linux freezes, when this warning appear, because I have some streaming over WiFi, and in the same moment when this happen I lose couple of packets. 
    After some time (I suppose when  latency is set to large enough value) this warnings doesn't appear, and I don't lose packets.

    So, my questions are:
    Why this happens?
    How I can resolve this issue?
    Is there any way to read this latency value and set to some higher value?

    Regards,
    Dragan

     
    steven.eckhoff
    Basic Member
    Basic Member
    Posts:192


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    21 Nov 2013 08:54 AM
    Zile,

    The message originates from the following function. This has to do with wakeup latency.

    /**
    * _omap_device_activate - increase device readiness
    * @od: struct omap_device *
    * @ignore_lat: increase to latency target (0) or full readiness (1)?
    *
    * Increase readiness of omap_device @od (thus decreasing device
    * wakeup latency, but consuming more power). If @ignore_lat is
    * IGNORE_WAKEUP_LAT, make the omap_device fully active. Otherwise,
    * if @ignore_lat is USE_WAKEUP_LAT, and the device's maximum wakeup
    * latency is greater than the requested maximum wakeup latency, step
    * backwards in the omap_device_pm_latency table to ensure the
    * device's maximum wakeup latency is less than or equal to the
    * requested maximum wakeup latency. Returns 0.
    */
    static int _omap_device_activate(struct omap_device *od, u8 ignore_lat)

    Which CPU governor are you using? (i.e. cat /sys/devices/system/cpu/cpu0/cpufreq/scaling_governor)

    Try setting this to performance and see if these messages go away.
    Zile
    New Member
    New Member
    Posts:45


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    18 Mar 2014 05:58 AM
    Hello,

    Problem was because kernel freezes when messages with printk is printed from kernel. Everytime when some message from kernel is printed I lose couple of packets. I commented these warnings with device latency.

    Regards,
    Zile

    Forums Board Support Packages (BSP) Linux
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