CODEWITHSUNDEEP
linuxraspberry-pi3yoctoopenembedded
vsecades
vsecades

Reputation: 124

Dallas 1 Wire Protocol with Yocto/Raspberry Pi 3

I have been trying to get a custom Yocto build off the ground for some time now. The goal is to connect a DS18b20 thermometer to the GPIO pins and test that it is indeed working. I have gotten as far as building out the base image and adding on all of the software packages I needed to it. The problem presents itself when I try to connect and detect the thermometer with my custom firmware image. It boots fine, networking works, wifi works, have not tried BT yet as I don't need it, but the GPIO pins are the ones that are not proving to be of help.

I am using a 4.9.x Linux Kernel on it. Is it recommended I downgrade to a 4.4.x Linux Kernel? I've pretty much run out of ideas at this point, just need some help to figure it out. f

Upvotes: 0

Views: 646

Answers (1)

TundraMan
TundraMan

Reputation: 51

This device is supported by the kernel, no need to mess with searching or writing your own w1 driver.You will need to ensure the CONFIG_W1_SLAVE_THERM, CONFIG_W1_MASTER_GPIO and CONFIG_W1 are set in you kernel config (consult the Yocto kernel documentation for setting this one-time or in a way that will persist over several builds).

This usually leaves the only remaining gap being which GPIO pin is used for w1. Without knowing which device you are using I can only provide some pointers. The connection is defined via a platform data. This can be defined in the device tree, for example with a c.h.i.p.

    onewire {
            compatible = "w1-gpio";
            gpios = <&pio 3 2 GPIO_ACTIVE_HIGH>; /* PD2 */
            pinctrl-names = "default";
            pinctrl-0 = <&chip_w1_pin>;
    };

Where PD2 == LCD-D2 on the header.

Alternatively it can be defined in the mach-* in the kernel, for example

static struct w1_gpio_platform_data w1_gpio_platform_data = {
        .pin                    = GPIO_ONE_WIRE,
        .is_open_drain          = 0,
};

static struct platform_device raumfeld_w1_gpio_device = {
        .name   = "w1-gpio",
        .dev    = {
                .platform_data = &w1_gpio_platform_data
        }
};

A google search of 'w1-gpio map gpio' should return more and better details. If you can use the device tree approach, that is what they are made for. Just know that the kernel code doesn't cycle through the GPIO pins looking for connected w1 devices, this mapping has to be set.

If the device is attached and working you will be able to get its value by doing 'cat /sys/bus/w1/devices/28*/w1_slave'. If you are using python you can use https://github.com/timofurrer/w1thermsensor to make reading the temperature easy. Or use equivalent libraries for your preferred language.

Upvotes: 1

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