i.MX ProcessorsのトピックRe: i.MX6: Using GPIO1_IO19

i.MX6: Using GPIO1_IO19

lynix — Mon, 03 Aug 2015 12:57:08 GMT

My intent is to configure the WDOG1 pin on the i.MX6 as GPIO output (to trigger a custom power-off circuit). The i.MX6 Reference Manual states that this is achievable by setting the Pad Mux Register (IOMUXC_SW_MUX_CTL_PAD_SD1_DATA2) MUX_MODE to ALT5, which selects the signal GPIO1_IO19.

In order to implement this, I have added the following lines to the iomuxc-block in the Linux Kernel device tree:

gpio19 {

pinctrl_gpio19_1: gpio19grp-1 {

fsl,pins = <

MX6QDL_PAD_SD1_DAT2__GPIO1_IO19 0x80000000

};

From userspace I am now able to configure and use the GPIO like this:

$ echo 19 > /sys/class/gpio/export

$ echo out > /sys/class/gpio/gpio19/direction

$ echo 1 > /sys/class/gpio/gpio19/active_low

$ echo 1 > /sys/class/gpio/gpio19/value

(unfortunately I don't have a scope so I can't verify that the output value actually changes)

My question now is how to do this initialization in the device tree, so that I have the GPIO properly set up on system boot without using userland scripts?

My understanding is that I'd have to create a "gpio19" device in the tree that makes use of the pinctrl block I have defined, but I don't know how to declare such a device. This document describes properties for such a device that I don't know which values I'd have to assign to, e.g. the interrupt number.

I'm using a TQMa6S board with the latest BSP 0105.

Thanks in advance for any feedback! :smileyhappy:

Re: i.MX6: Using GPIO1_IO19

frankba — Mon, 03 Aug 2015 15:21:07 GMT

Hi Alexander,

not sure if I got your question right. A common trick is to use the GPIO as a LED. In the device tree, insert a block like:

/ {
...
    leds {
        compatible = "gpio-leds";
        my_led {
            gpios = <&gpio1 19 GPIO_ACTIVE_LOW>;
        };
    };
...

which will automatically create a LED that can be switched on and off:

echo 1 > /sys/class/leds/my_led/brightness
echo 0 > /sys/class/leds/my_led/brightness

Frank

Re: i.MX6: Using GPIO1_IO19

BiyongSUN — Tue, 04 Aug 2015 10:20:59 GMT

Please check the base and lable to indetify the number of gpio in linux.

GPIO1_19 should be the GPIO1 base + 19.

for example:

root@imx6qdlsolo:~# cat /sys/class/gpio/gpiochip32/base

root@imx6qdlsolo:~# cat /sys/class/gpio/gpiochip32/label

20a0000.gpio

Re: i.MX6: Using GPIO1_IO19

lynix — Tue, 04 Aug 2015 11:02:46 GMT

Exactly what I was looking for, thanks! :smileyhappy:

Re: i.MX6: Using GPIO1_IO19

lynix — Tue, 04 Aug 2015 11:04:38 GMT

Thank you for the hint; I was naive and assumed it to be 19.

Check according your hint confirmed that:

root@MBa6x:~ cat /sys/class/gpio/gpiochip0/base

(There is no /sys/class/gpio/gpiochip1, I think they are just indexed by 0)

Re: i.MX6: Using GPIO1_IO19

BiyongSUN — Wed, 05 Aug 2015 04:56:01 GMT

what is the lable?

It is the value to indentify the gpio, which is in the device tree.

In that way, you can figure out which is the base for.