Disabling/Enabling USB Host Power

[AndrewTaneGlen]

Hello,

With my BBB I've been using a usb wifi device that that appears to crash unrecoverably occasionally, but always works again if I simply unplug it and plug it back in.

With this in mind I've been looking for ways to disable the USB host power output and re-enable it, in order to programmatically reset any usb device I have connected.

Looking at the BBB schematic there is a 'USB1_DRVVBUS' output from the uC which controls the USB host 5V output. Does anyone know if it is possible manipulate this pin as a gpio in order to disable/re-enable the 5V USB output, or is this necessarily controlled by the USB phy, with any manual control breaking the USB functionality.

The document spruh73h.pdf describes how after asserting the 'USB1_DRVVBUS' output the USB phy looks for the 5V to come up, and if not detected within 100ms it flags a fault - possibly once this has been faultlessly enabled this problem is no longer looked for - soed anyone have any idea before I possibly start breaking things?

Regards,

Andrew Glen.

[AndrewTaneGlen]

To answer my own question, here are the steps to take control of the USB1_DRVVBUS signal from user space:

Note: I am using Debian Wheezy (7.2) and Kernel 3.12

1) Ensure you have the device tree compiler patched/built. Do not use the apt-get package, instead, follow steps here:

http://www.embedded-things.com/bbb/patching-the-device-tree-compiler-for-ubuntu/

2) Create a .dts file (called 'USBCONTROL-Test.dts' in this example), with something like the following contents:

/* Information: 

*/

/dts-v1/;
/plugin/;

/{
    compatible = "ti,beaglebone", "ti,beaglebone-black";
    part-number = "USBCONTROL-Test";
    version = "00A0";

    fragment@0 {
        target = <&am33xx_pinmux>;

        __overlay__ {
            usb_drvvbus_pin: usb_drvvbus_pin_mux {
                pinctrl-single,pins = <
                    0x234 0x07 /* Pin 131 - gpio3.13 */
                >;
            };
        };
    };

    fragment@1 {
        target = <&baseboard_beaglebone_black>;

        __overlay__ {
            usb_power_signals {
                pinctrl-names = "default";
                pinctrl-0 = <&usb_drvvbus_pin>;

                compatible = "gpio-leds";

                led@8 {
                        label = "usb1_drvvbus";
                        gpios = <&gpio3 13 0>;
                        linux,default-trigger = "none";
                        default-state = "on";
                        status = "okay";
                };
            };
        };
    };
};

3) Compile the dts file to a blob with the following command:

dtc -O dtb -o USBCONTROL-Test-00A0.dtbo -b 0 -@ USBCONTROL-Test.dts

4) Copy the output .dtbo file to /lib/firmware:

cp USBCONTROL-Test-00A0.dtbo /lib/firmware

5) Now we're ready to take control of this signal. First, unbind the usb driver; this disables all connected devices - this prevents instability when cutting the power:
echo '2-1' | tee /sys/bus/usb/drivers/usb/unbind

6) No load the device tree file - this immediately changes the mux settings, changing the function of pin usb1_drvvbus to gpio3_13, and allowing control of this pin via the led driver:
echo USBCONTROL-Test:00A0 > /sys/devices/bone_capemgr.6/slots

7) Now set the signal to ON (re-enabling the USB Host 5V supply):
echo 1 > /sys/devices/usb_power_signals.8/leds/usb1_drvvbus/brightness

8) Reload the USB Driver for USB1 - this will cause all connected drivers to be reloaded from scratch:
echo '2-1' | tee /sys/bus/usb/drivers/usb/bind