You do not have two programs. You have one program that requires compiling two C source files and linking them together into one executable object file.

What is minicom? If it works with minicom what are you using when it fails?

What operating system are you using?

What compiler are you using? What command line are you using to compile and link the various pieces of this program.

So, why is the inclusion of termios.h commented out when you are clearly getting warnings because you haven't included that header? And, why are you including asm/termios.h?

You declare that scale9() will return a floating point value, but there are no return statements in scale9() (so it can't possibly return a value).

There is clearly other code in what you have shown us that would generate compilation errors (not just warnings). (strip the first character, which is a carriage return is not a valid C statement.) Please show us your real code; not code that has been modified to spread comments across multiple lines.

The way you are setting options.c_cflag is clearly wrong, but I'm not sure how to correct it since I'm not sure what you're trying to do. What terminal characteristics does the scale connected to /dev/ttyS0 expect?

Please show us the output you get from the command:

Code:

od -bc < /tmp/testfile.txt

after you run your program.