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ccompilationi2craspberry-pi4smbus
mjarvas
mjarvas

Reputation: 11

Can't compile i2c_smbus_write_byte on Raspberry Pi 4

Has anybody tried using the i2c_smbus_write_byte or any similar function on Raspberry Pi 4?

I can't get it to compile; it fails at the linking with not finding it. I'm using it as described here: http://synfare.com/599N105E/hwdocs/rpi/rpii2c.html

All the headers recommended are there is and also the -li2c in the Makefile. What might the problem can be?

Upvotes: 0

Views: 3067

Answers (2)

Jari Jokinen
Jari Jokinen

Reputation: 770

The page you are linking to says:

With the Buster version, as of june 2019, the necessary details for using i2c_smbus_write_byte_data() and siblings, require the following include statements:

#include <unistd.h>
#include <fcntl.h>
#include <sys/ioctl.h>
#include <linux/i2c-dev.h>
#include <i2c/smbus.h>

Using fgrep you can confirm that the function is declared in the /usr/include/i2c/smbus.h:

# cd /usr/include; fgrep -R i2c_smbus_write_byte *
i2c/smbus.h:extern __s32 i2c_smbus_write_byte(int file, __u8 value);
i2c/smbus.h:extern __s32 i2c_smbus_write_byte_data(int file, __u8 command, __u8 value);

So this should work:

#include <unistd.h>
#include <fcntl.h>
#include <sys/ioctl.h>
#include <linux/i2c-dev.h>
#include <i2c/smbus.h>

int main(void) {
  int i2c = open("/dev/i2c-1", O_RDWR);
  i2c_smbus_write_byte(i2c, 1);
  close(i2c);
  return 0;
}

I tested that this example compiles successfully in the latest Raspbian Buster Lite:

gcc test.c -otest -li2c

If you are using g++ instead of gcc, then you should wrap the include directives with extern "C":

extern "C" {
  #include <linux/i2c-dev.h>
  #include <i2c/smbus.h>
}

Upvotes: 1

nivpeled
nivpeled

Reputation: 1838

Might be worth checking to see if libi2c-dev is present on your system.

sudo apt-get install libi2c-dev

may be all that you need.

Upvotes: 1

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