vesas
Posts: 2
Joined: Tue May 09, 2017 7:00 am

w1-gpio and w1-gpio-pullup parasitic mode disabled

Tue May 09, 2017 7:48 am

I,m tryingin use w1-gpio and w1-gpio-pullup on parasitic mode, but it seems that current kernel do not support pullup=1 option. Both drivers gives on dmessage same info:

w1_add_master_device: set_pullup requires write_byte or touch_bit, disabling

When checking io-pin with scope, there is no sharp up edeges on DQ so dmesg gives right status, active pull up is disable. Also with w1-gpio-pullup there is no any activity on second gpio. Second gpio should drive external mosfet for pulling up DQ during data idle time for chargin parasitic capacitor on 1-wire sensor.

Proper functionality for w1-gpio-pullup second io-pin is explained on ds18b20 datasheet or any other 1-wire documents. With settings:
dtoverlay=w1-gpio-pullup,gpiopin=4,pullup=1,extpullup=5

gpio4 is for DQ data only and gpio5 is high during data trasmissin (mosfet not pulling DQ high) and low during DQ idle time(mosfet pulling DQ high).

Is there any plans to add support pullup=1 option for w1-gpio and w1-gpio-pullup driver?

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DMike92
Posts: 21
Joined: Mon Dec 29, 2014 12:52 am
Location: France
Contact: Website

Re: w1-gpio and w1-gpio-pullup parasitic mode disabled

Tue Jan 16, 2018 3:10 pm

gpio4 is for DQ data only and gpio5 is high during data trasmissin (mosfet not pulling DQ high) and low during DQ idle time(mosfet pulling DQ high).
Hi,
I'm not using parasitic modes on any of my probes but mosfet should not pull DQ high all the idle time otherwise probes could not pull DQ low.
This is why, in my opinion, another GPIO is used to control the mosfet and activate it a short time.

I agree this does not solve/answer your problem :-)
Le savoir ne vaut que quand il est partagé (c'est pas de moi mais j'adhère).

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