Supervisory circuit (APX823-31W5)

Discussion in 'General Discussion' started by raphui, Feb 12, 2014.

  1. raphui

    raphui New Member

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    Nov 22, 2013
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    Hello,

    I see in the schematics, that there is a supervisory circuit handle by the APX823-31W5 ( U117 ) chip.

    By reading the datasheet of this chip, it's written that the WDI signal ( in udoo case it's WDT_TRG ) has to be periodically triggered by a positive or negative transition to avoid the reset of the system ( because the RESET# pin is connected to the IMX_PORB of the imx6 ).

    I wonder how this is handle in u-boot ? I've seen this function :

    Code:
    
    static iomux_v3_cfg_t const wdog_pads[] = {
    	MX6_PAD_EIM_A24__GPIO_5_4 | MUX_PAD_CTRL(NO_PAD_CTRL),
    	MX6_PAD_EIM_D19__GPIO_3_19,
    };
    
    static void setup_iomux_wdog(void)
    {
    	imx_iomux_v3_setup_multiple_pads(wdog_pads, ARRAY_SIZE(wdog_pads));
    	gpio_direction_output(WDT_TRG, 0);
    	gpio_direction_output(WDT_EN, 1);
    	gpio_direction_input(WDT_TRG);
    }
    
    But i don't understand why WDT_TRG is in input and how u-boot trigger WDT_TRG periodically...

    Someone can explain me ?

    Thanks :)
     
  2. Abdelrahman

    Abdelrahman New Member

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    Jul 21, 2015
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    Hello raphui,

    I think that's due to that "Leaving WDI unconnected disables the watchdog" (source: the chip datasheet).
    So when this pin becomes an input it acts as it's unconnected.
    I hope that to be helpful.

    Regards,
    Abdelrahman
     

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