GPIO bias-pull-up electrical observation

Tachyon
1

We've observed the kernel debug logs show "no pull", or "pull down" on input pins but input value is high, for instance...
sudo grep "gpio147" /sys/kernel/debug/gpio

gpio147 : in high func0 2mA pull down(note the in high is with nothing external connected)

GPIO147 according to the Input/Output section Input / Output | Particle Developer is muxed to LPI_MI2S_DATA1, however the live device tree does not mention gpio147.

We measured the voltage across a 5kohm resistor between gpio147 and ground and got ~.3V

5000ohm × ( 3.3V ÷ 0.382V - 1 ) = 38,193.717ohms (~47kohms)

We adjusted our pull down from 10k to 4.7k to overcome this pull-up resistance.

Is this external pull-up resistance expected on Tachyon input gpios? Is there another way to set the bias to remove this resistance?

{
"distro": {
"board": "formfactor_dvt",
"distribution": "ubuntu",
"distribution_version": "24.04",
"region": "NA",
"stack": "ubuntu-desktop-24.04",
"variant": "desktop",
"version": "1.1.43"
},
"src": {
"overlays": "HEAD",
"tachyon_composer": "1.1.43",
"u_boot": "1.0.30",
"ubuntu_20_04": "1.0.180",
"ubuntu_24_04": "22-938ac1d"
}
}

2

I don't know this for sure, but I suspect it has to do with the TXS0108E bi-directional level translators. The QCM6490 runs at 1.8V but the HAT connector is 3.3V I/O with 5V tolerance. Because the direction is auto-sensing, it's possible to confuse it, especially in open-drain mode.

3

Thanks for this info @rickkas7!!! The pin in question gpio147, among others on the 40-pin ( e.g. gpios 32, 61, and 146 ) show high in the kernel debug gpio file even if they are set to pull-down or no-pull bias. And they are definitively high, like no fluctuation 3.3v all day long.

I do find your reference to the TXS0108E enlightening, so thank you. I'll have to look at the datasheet and figure out if it supports biases of its own, and if so how could one control those from the Tachyon...
gpio32: in high func0 2mA pull down
gpio61: in high func0 6mA no pull

gpio146 : in high func0 2mA pull down