Update gpio.md

jamescadd · Sep 20, 2020 · 36b9158 · 36b9158
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diff --git a/pages/gpio.md b/pages/gpio.md
@@ -153,10 +153,14 @@ The driver `gpio` provides access to regular GPIO pins with input and output mod
 
 You can use the [interactive scheme](https://pinout.xyz/) when selecting the pins to use. Please note that when selecting a pin for a channel, you need to use a logical number instead of a physical number. That is, if you want to use a physical pin with the number 40, the channel must have the number 21 corresponding to the logical GPIO21.
 
+Channels should not use duplicate pins. You can also not use already used pins. To see which pins are currently used, run the command `gpioinfo`.
+
 ### USB HID Relay
 The driver `hidrelay` provides access to cheap managed [USB HID relays](http://vusb.wikidot.com/project:driver-less-usb-relays-hid-interface) that can be found on AliExpress. This driver does not support input mode, only output. To use it, you need to specify the path to the device file (like `/dev/hidraw0`) using the `device` parameter.
 
 Additionally, we recommend to configure access rights and static device name using [UDEV rules](https://wiki.archlinux.org/index.php/udev). For example, create `/etc/udev/rules.d/99-kvmd-extra.rules`:
 ```
 SUBSYSTEM=="usb", ATTR{idVendor}=="16c0", ATTR{idProduct}=="05df", MODE="666"
 ```
+
+Channels should not use duplicate physical numbers.