I need help with gpio pins states during boot. I know that 5V and 3.3V pins send this voltage once the board powers on. However I wish to know whether GPIO pins send by default 1/on or 0/off when the board is powered up. I might have seen somewhere that some pins outputs 1 by default and others 0 (most of them), but I don’t remember where I could see it.
Anyways, my goal here is: when I Nano receives energy, I need to send a ON/1 signal via GPIO and set it OFF when the boot is completed.
Actually, my solution might be easier. I’m wiring my gpio17 (pin 21) to the base of a BC558 transistor which is responsible by turn on/off my buzzer. Since it’s a PNP transistor, during boot it should be low according to schematics so my PNP transistor would have its base triggered, right?
However it isn’t happening. What I noticed is that ONLY when I export gpio17 after system is already up that low/off/0 is INDEED sent through gpio17. Can you help me with it? I’m not quite sure how to proceed here.
Many of the GPIOs are “input” rather than “output” when booting, and may or may not have a pull-up/down resistor (which, in turn, could be 18kOhm or 100kOhm depending on the pin.)
Since I’m not quite familiar with electrics, I have to ask: How can I check in which case each pin is? I’m not quite sure wheter is safe or not to just add a 100k resistor and check if it works. I don’t want to fry my nano hehe.
The default behavior of each pin is documented in the Tegra X1 Technical Reference Manual, which is downloadable from the documentation site for Jetson developers. I think chapter 9 is the one about GPIO pins, if I remember right.
Beware, though, that the manual is written with all the information an engineer needs to correctly use the devices, but it is not a tutorial in electronics or registered I/O device development. Those are assumed pre-requisites, that you’d have to learn elsewhere first.
