Application Examples • 183
Example of Reading and Writing from the NVRAM
WAGO-I/O-SYSTEM 750
Linux Fieldbus Coupler
8.5 Example of Reading and Writing from the NVRAM
The NVRAM (Non Volatile Random Access Memory) is a non-volatile
memory that retains its information even after the Linux fieldbus coupler has
been switched off.
Benefit of the NVRAM:
•
Short access times similar to RAM.
•
Can be written to like a RAM
•
Storage of data in the event of power loss similar to flash memory.
Access to the NVRAM
Access to the NVRAM is done via the
nvram
device file which is located in
the
dev
directory of the Linux fieldbus coupler. The NVRAM can be written
and read byte by byte. The following functions allow user space access to the
NVRAM:
•
int open (const char *
pathname
, int
flags
);
This function opens the indicated file and returns the file descriptor. The
file descriptor is a reference to the open file.
pathname:
Path of the device file:
/dev/nvram
flags:
O_WRONLY, O_RDONLY, O_RDWR
•
ssize_t read(int
fd
, void *
buf
, size_t
count
);
This function reads a specified number of bytes from the referenced file
and returns the number of bytes read.
fd:
File descriptor returned by the
open
function.
buf:
A pointer to the buffer into which to read the data.
count:
Number of bytes to be moved to the target buffer.
•
ssize_t write(int
fd
, const char *
buf
, size_t
count
);
This function writes a specified number of bytes to the referenced file and
returns the number of bytes written.
fd:
File descriptor returned by the
open
function.
buf:
A pointer to the buffer from which to write the data to the memory.
count:
Number of bytes to be written.
