This approach should be used for all boards that use a fixed device type. This ensures a safe operation, portability and easier handling of the underlying hardware. A user-space application should therefore first read the entire file, modify it and then write the entire buffer back. Thus it is possible to emulate parts of a keyboard or to create your own input device. The specified partitions are tied to parts. Therefore these values have to be provided in the board setup code. This may not be necessary if you already have build the kernel for your board.

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Adding support for a custom board makes it easier to maintain changes across kernel releases.

To be able to control a LED with this class, the board setup code must be modified, if not already done on Atmel boards e. A read will only succeed if new data is available. This is achieved through reading out the pin state in a distinct time period scan interval.

The configfs must then be mounted to a dedicated mountpoint. This means only if a GPIO has changed its status since the last read.

Use the —n flag to set the non-blocking method. The datasheet lists available external interrupt lines.


An entry like the following is needed: To get input states of a pin to user-space, use the gpio-keys driver. Valid device types are listed in the same file. The following command does the trick: This may not be necessary if you already have build the kernel for your board. An event is described by the following structure: This chapter is here because many use this interface already and maybe do not want to switch to another solution.

The configfs is a filesystem-based manager of kernel objects. The rest of the flash can be used to store the root file system or other data.

To fit this all together two more structures are needed.

For example an adaptation is necessary if the pin multiplexing should be different or unused peripheral pins should be used for other things. It will also be used to print the boot messages.

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The configuration of the SMC for a flash device needs three steps. For the above partitions the structure would be initialized like this: Use 0 for the first line, 1 for the second … G;io last parameter is a data structure that is defined as follows: To build the LED functionality into the kernel or as module, following options should be enabled in the kernel configuration Device Drivers LED devices: Also the path should point to the correct board.


Time in milliseconds during which the LED should be turned on? A kernel-space access to a GPIO is fast and short interrupt response times can be achieved, thus it is best to implement a protocol here. Run the program with the flag —h to get all available options.

This is the standard method when opening files on Linux. The pin number can be calculated by using the macros in the file at32ap Unless specifically provided otherwise, Atmel products are not suitable for, and shall not be used in, automotive applications.

View detail for AVR32744: 32-bit AVR AP7 Linux Custom Board Support

These parameters should be set in the board setup code if needed. The hexdump program will print out the four bytes as a nice hexadecimal value. Also if modules have dependencies within linuc other the initialization sequence is important. If the board has its own configuration options an additional entry is needed. Take a look at chapter 3 on how to configure GPIOs. Here, we have full control of all the pin settings.