Am 19.09.2016 um 10:42 schrieb Colin Law:
> On 4 September 2016 at 19:59, Jan Kandziora <j...@gmx.de> wrote:
>> Am 04.09.2016 um 19:08 schrieb Colin Law:
>>> To summarize then, for parasitic mode I should not need an external
>>> strong pullup and should be able to use just a 1.5k pullup and to
>>> sudo modprobe w1-gpio pullup=1
>>> With in addition the 3.3 to 5V level shifter as in your first post if
>>> any devices on the bus need 5V
> Sorry, I need yet further clarification on this. I have been trying
> to get to grips with device tree and (on pi with raspbian jessie) in
> /boot/overlays/README it says
> "Device Tree makes it possible
> to support many hardware configurations with a single kernel and without the
> need to explicitly load or blacklist kernel modules."
> which I think means that it should not be necessary to use modprobe
> w1-gpio or to put the module in /etc/modules.
This is a misunderstanding.
If you don't modprobe the module, someone else has to do. It depends on
your udev setup whether udev does it for you. The kernel doesn't load
modules automatically just because a device is listed in the loaded
Before device trees, hardware layout has been hardcoded in the driver
modules or have to be specified by module options. That's what is no
> Also for w1-gpio it has
> "Name: w1-gpio
> Info: Configures the w1-gpio Onewire interface module.
> Use this overlay if you *don't* need a GPIO to drive an external
> Load: dtoverlay=w1-gpio,<param>=<val>
> Params: gpiopin GPIO for I/O (default "4")
> pullup Non-zero, "on", or "y" to enable the parasitic
> power (2-wire, power-on-data) feature
> Does this mean I can (should?) use
Haven't checked yet. Technically it is possible to use the internal push
transistor of the GPIO port to act as a strong pullup.
HOWEVER, you should use a series resistor outside the GPIO port then.
Because, overcurrent from shorting the Onewire too long may kill the
GPIO4 push transistor inside the BCM2835 SoC.
> and remove the modprobe command?
Check with lsmod whether the module gets loaded automatically by udev.
Owfs-developers mailing list