Note the structure here form this modified file( Modified from Charles S'
Universal IO overlay 'univ-all' ) This is for a single pin instead of all
pins.
https://github.com/beagleboard/bb.org-overlays/blob/master/src/arm/univ-all-00A0.dts
IN short here is what is required:
- /dts-v1/;
- /plugin/;
- / {
- compatible = "ti,beaglebone", "ti,beaglebone-black",
"ti,beaglebone-green";
- part-number = "univ-P8_07";
- version = "00A0";
Passed that exclusive-use = "P8.7"; ive seen in each overlay for pins
each uses. BUt if you examine this file closely it should become apparent
what is required to make a like overlay function. This specific file is
mean to offer the ability to change pin mux dynamically as the system is
running. So there are 5 possibilities from this file, but initially the pin
is configured as input.
I will tell you what helps me a good bit while editing device tree files.
You need a good editor that will allow you to arbitrarily set syntax
highlighting. Then, I personally set syntax highlighting to "C".
/dts-v1/;
/plugin/;
/ {
compatible = "ti,beaglebone", "ti,beaglebone-black",
"ti,beaglebone-green";
/* identification */
part-number = "univ-P8_07";
version = "00A0";
/* state the resources this cape uses */
exclusive-use = "P8.7";
/* P8_07 (ZCZ ball R7 ) */
P8_07_default_pin: pinmux_P8_07_default_pin {
pinctrl-single,pins = <0x090 0x37>; }; /* Mode 7, Pull-Up,
RxActive */
P8_07_gpio_pin: pinmux_P8_07_gpio_pin {
pinctrl-single,pins = <0x090 0x2F>; }; /* Mode 7, RxActive */
P8_07_gpio_pu_pin: pinmux_P8_07_gpio_pu_pin {
pinctrl-single,pins = <0x090 0x37>; }; /* Mode 7, Pull-Up,
RxActive */
P8_07_gpio_pd_pin: pinmux_P8_07_gpio_pd_pin {
pinctrl-single,pins = <0x090 0x27>; }; /* Mode 7, Pull-Down,
RxActive */
P8_07_timer_pin: pinmux_P8_07_timer_pin {
pinctrl-single,pins = <0x090 0x32>; }; /* Mode 2, Pull-Up,
RxActive */
fragment@1 {
target = <&ocp>;
__overlay__ {
P8_07_pinmux {
compatible = "bone-pinmux-helper";
status = "okay";
pinctrl-names = "default", "gpio", "gpio_pu", "gpio_pd",
"timer";
pinctrl-0 = <&P8_07_default_pin>;
pinctrl-1 = <&P8_07_gpio_pin>;
pinctrl-2 = <&P8_07_gpio_pu_pin>;
pinctrl-3 = <&P8_07_gpio_pd_pin>;
pinctrl-4 = <&P8_07_timer_pin>;
};
};
};
fragment@2 {
target = <&ocp>;
__overlay__ {
cape-universal {
compatible = "gpio-of-helper";
status = "okay";
pinctrl-names = "default";
pinctrl-0 = <>;
P8_07 {
gpio-name = "P8_07";
gpio = <&gpio2 2 0>;
input;
dir-changeable;
};
};
};
};
};
On Mon, Jul 25, 2016 at 10:53 AM, Raul Piper <[email protected]> wrote:
> Hi Greg,
> Thankyou for the elaborative post and the link you sent.My understanding
> is mainly theoretical and inlined with what you wrote..
>
> Yes,I have been scanning across many links on google and stack overflow
> but not able to find single one convincing.
>
> I came to conclusion that i will write a hello world gpio driver with lots
> of printk and build it along with the dts file by placing it in
> arch/arm/boot/dts and then loading that kernel image.According to
> R.Nelson's link i will copy the dtb files as well.
> Init--> probe-->register platform driver(.compatible string in the
> platform_device structure ) should throw something to go ahead with then.
>
> But still the loop holes in the understanding like why to copy all the dtb
> files,how to build only that dtb file and copy it in the lib/firmware and
> dynamically insmod the driver ....where does overlays come into the
> picture...can the drivers without dtb implementation be accepted in
> kernelmain line...
>
> Really looking for some example code here.
>
> On Monday 25 July 2016, Greg <[email protected]> wrote:
>
>> I'm not sure there is a one-stop shop for understanding the Device Tree
>> anywhere.
>>
>> There are at least 4 file types involved:
>>
>> 1. dts- This is the source code (text file) which is a data structure
>> to describe hardware.
>> 2. dtsi- A sub-chunk or "include" file which is used inside dts files.
>> It's somewhat similar to an "include" or "import" in programming languages.
>> 3. dtb- Device tree blob. This is the compiled version of the dts.
>> This is what gets loaded at boot time. It's the foundation of the system
>> used by the kernel.
>> 4. dtbo- Device tree overlay. This can be loaded after boot time.
>> This is how the Beaglebone adjusts itself when different "capes" are
>> plugged in. It does this by reading information stored in the EEPROM in
>> the cape. These "overlays" can also be loaded at the command line using
>> the "slots" in the sysfs virtual file system. Look for a substantial
>> collection of already done overlays in the directory /lib/firmware. If you
>> want to make your own overlay, /lib/firmware is where you want to place it.
>>
>> This topic is really confusing, and no doubt my notes above are full of
>> flaws.
>>
>> You can work through and understand all of the above. However, depending
>> on the complexity of what you are trying to do, this may be sufficient:
>>
>> https://github.com/cdsteinkuehler/beaglebone-universal-io
>>
>> Using the config-pin -f option and a simple text file you can use your
>> .profile or similar start-up configuration file to set the pins to your
>> requirements.
>> This is a relatively straight-forward solution to tacking the problem.
>>
>> In my opinion the device tree is a major hurdle to making progress with
>> the Beaglebones. If you google you will get a bunch of out-dated
>> information, so be careful what you read on the net. Perhaps someone will
>> suggest single source of accurate information on this topic.
>>
>> Regards,
>> Greg
>>
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