Modified default code gives "code violation"

[heydowns]

You probably get code errors because of your printf statements:

unsigned char joystick_input = 127;
 // ...
printf("Slow_Drive for pwm01 = %d",joystick_input); 
// ...
printf("Slow_Drive for pwm02 = %d",joystick_input);

You are asking printf to print an integer type (by using %d). But you are only passing it an "unsigned char" data type. In brief, this is in error -- details are below.
To fix, try passing it an unsigned integer explicitly by doing the following:

printf("Slow_Drive for pwm01 = %u", (unsigned int)joystick_input);

The %u says "print as unsigned". The cast to unsigned int will ensure that the arguments are decoded correctly within the printf function.

For those interested, the long explanation:
printf takes a variable number and type of arguments. This is contrary to most functions, which have a very specified number and type of arguments (void f(int x, int y) takes two ints, for example).

Printf relies on you supplying the correct format characters in the initial string argument to be able to decode the subsequent arguments. This is so that it can grab the right number of bytes off the block of memory representing the passed arguments. If you put a format character for int (%d), it will grab sizeof(int) bytes. If you put a format character for char (%c), it will grab sizeof(char) bytes. And so on.

The original poster's code specified %d as the format string, but passed a char. This means the printf code went to grab 2 bytes (sizeof int), but, in reality, the function was only passed 1 byte (sizeof unsigned char). This resulted in printf accessing memory outside the space allocated to the function's arguments.

In this case, it resulted in red light of doom..... But that isn't necessarily always the case. The results here really are undefined and unpredictable. There is a chance it would just run, probably printing out incorrect results for the passed unsigned char.

Another common mistake with printf is when printing long variables. You need to use %ld (for long) or %lu (for unsigned long). If you accidentally use %d for long, you'll likely just get wrong output, but not red light of death.