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Arcom Embedded Linux Technical Manual Developing software for AEL

Common embedded software development tasks

Accessing the physical address space

When developing software for AEL, it is sometimes necessary to access the

processor’s physical address space from within your application. For example, you may

need to tweak memory mapped register settings within the CPU or to access some

external peripheral such as a GPIO pin.

A Linux application may only access the virtual address space that the Linux kernel has

created for it. This virtual address space normally does not contain mappings to the

physical regions that you want to use. An application can create a mapping to an

arbitrary physical address by opening the /dev/mem special device file, which provides

access to the entire physical address space, and then performing an mmap() operation

on the file handle.

For security reasons, the application must be running as root in order to do this.

Getting the specifics of this operation correct can be tricky, so we provide a library

(libdevmem) that handles this complexity for you. The library provides a number of

functions:

libdevmem_handle libdevmem_open(unsigned long base,

unsigned long length);

int libdevmem_close(libdevmem_handle handle);

TYPE

_t libdevmem_read_

TYPE

(libdevmem_handle handle,

unsigned long offset);

void libdevmem_write_

TYPE

(libdevmem_handle handle,

unsigned long offset,

TYPE

_t value);

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Eurotech ZEUS Bedienungsanleitung Seite 47