Types of addressing modes

There are three kinds of addressing modes - virtual addressing, physical addressing and system bus addressing. To learn the details, turn to Page 6 of the datasheet.

The macro __io_address implemented in the probe function of the driver returns the virtual address of the physical address passed as an argument. For GPIO, the physical address is 0x20200000(0x20000000 + 0x200000), where 0x20000000 is the base address and 0x200000 is the peripheral offset. Turn to Page 5 of the datasheet for more details. Any guesses on which address the macro __io_ address would return? The address returned by this macro can then be used for accessing (reading or writing) the concerned peripheral registers.

The GPIO control application is analogous to a simple C program with an additional ioctl call. This call is capable of passing data from the application layer to the driver layer with an appropriate command. I have restricted the use of other GPIOs as they are not exposed to headers like others. So, modify the application as per your requirements. More information is available on this peripheral from Page 89 of the datasheet. In this code, I have just added functionality for setting or clearing a GPIO. Another interesting feature is that by configuring the appropriate registers, you can configure GPIOs as interrupt pins. So whenever a pulse is routed to that pin, the processor, i.e., ARM, is interrupted and the corresponding handler registered for that interrupt is invoked to handle and process it. This interesting aspect will be taken up in later articles.