How can we find the naming of available gpios in an arbitrary board that runs Linux and then to use the Linux commands echo "gpionumber" >/sys/class/gpio so then we can control this gpio?
Gpio and gpiocontrollers are numbered. Gpiocontrollers may have labels, but they may not be unique.
The linux kernel documentation on gpio sysfs driver can be found here and is a good read.
The linux kernel uses device tree file to know which gpiocontrollers are available to him. A gpiocontroller may have multiple gpios. Each board has it's own unique device tree compiled with the kernel or loaded at boot time.
Gpiocontrollers are identified by the register and register length they refer too, see here. You can specify the label of the gpiocontroller as described in device tree file format and you can query the gpiocontroller label using /sys/class/gpio/gpiochipN/label, they may be not unique and they don't let you identify the gpio. Also, they may change between device tree file versions.
There is no "naming", just numbering. You can query all gpios available on a particular board by just inspecting/adding the /sys/class/gpio/gpiochip*/ngpio Usually a board manufacturer/provider/seller/etc provides documentation with the kernel it ships with the board with explanation, which gpio has which number/address, like for Colibri VF61. For some popular boards it is just a matter of googling to find nice looking images with gpio numbers, like for RaspberryPi3 or
Related
In most example project for embedded system there is a system file in which we can find structures for different peripheral as well as the memory mapping of the peripheral register, in addition there is also a module per peripheral that contains basic function to manipulate the periheral like: periph_enable, periph_write, periph_read; this is the architecture i have in mind when i tackle a new project.
Actually i started to work with a BF609 but now with an embedded linux in it, my task consist in writing a communication driver with another device via UART, as usual i tried to look for the files i used to use but in vain, i can't find the mapping of the different peripheral.
I started to read this book, i undrestand that the kernel see each device like a file and that a driver is mainly the implementation of the open, close, read and writefunctions in these file but i still don't undrestand how these functions communicate with peripheral registers.
My questions:
1) How device drivers recognise the mapping of the peripheral is there sth i missed, is there any example that explain how to implement simple read and write functions via UART for example
2) Where can i find the mapping of the peripheral in the buildroot directory
Thanks in advance
So I have a Beaglebone black, and a servo/led controller http://www.adafruit.com/product/815. I'd like to control it from a C/C++ program running on the included Debian Linux.
I see there is a driver included in the kernel "pwm_pca9685", and it did create some items in the /sys directory, but nothing that seems to make any sense.
So I know that at least I need to tell the module what i2c address the chip has, so how would I do that, and then how to send various pwm commands to chip?
So I ended up forgoing the use of the driver, as I was unable to find any information on it. Instead I used various ioctl calls, such as is used in this code from Adafruit: https://github.com/adafruit/Adafruit-PWM-Servo-Driver-Library/blob/master/Adafruit_PWMServoDriver.cpp
I have booted a ubuntu on a ZedBoard. I want to transfer data between fpga and linux. For example, I want to write or read a register from linux. What is best way for doing it? I have not any idea.
Thanx.
First of all, you need to specifically say what you want to do, for example. if you want to access the IO signals on the FPGA, you need to first add the GPIO module to your system, synthesize and implement it.
Then you use the Linux GPIO Driver to access the port as it is explained in this page:
Linux GPIO Driver
The GPIO driver fits in the Linux GPIO framework which is not a char
mode driver. Yet it does provide access to the GPIO by user space
through the sysfs filesystem. This allows each GPIO signal to be read
and written in similar manner to a char mode device. The interface is
somewhat documented in the kernel tree at Documentation/gpio.txt. The
following text is aimed to augment, not replace the existing
documentation.
For other, more complex interfaces you need to create your own driver or use one of the drivers that are available and modify it to fit your needs.
I am using Ubuntu 11.10. I have written a driver for a GPIO chip which did not have its own driver in the kernel.
I want to place a restriction on users from setting output-only pins to inputs, and vice-versa when using /sys/class/gpio. This is because many of the GPIO's on my board are input only or output only.
I could scan for restricted GPIO numbers from within the functions gpio_direction_in(), gpio_direction_out() and gpio_request() but I think that's a bit of a hack-around.
Is there any function especially for this purpose? I looked through the documentation for GPIOs but I couldn't see anything.
Andrew
I have just ported uboot and the linux kernel to my imx31 based board. The kernel boots up because I can see the kernel messages in the ring buffer in ram, but I am not seeing and text on the serial port after ... decompressing kernel, done, booting kernel"
I am passing "console=ttySMX0,115200" on the kernel arguement line, but I am not seeing the serial device being probed by the kernel (the serial driver is being registered, but no probe is happening).
I don't understand the relationship between the serial console name "ttySMX" and what the kernel expects.
I have built the kernel under openembedded with support for the LogicPD liteboard and Freescale ADS31 board, as these are closest to my board.
Any help much appreciated ... I have been trying to get this going for two weeks.
Amongst other things need to have both CONFIG_SERIAL_IMX and CONFIG_SERIAL_IMX_CONSOLE selected in your kernel configuration.
It's possible these tags could have other names in your build. In the one I looked at, they were referenced in driver/tty/serial/imx.c - if there is a different file that embodies the driver in your build, look for similar options in its source and in the Makefile in that directory.