Globals go like this:

hwconf.c

int global_x = 123;

hwconf.h

extern int global_x;

Now you've got one copy of global_x, notionally stored in hwconf.c, but accessible to everyone who includes hwconf.h.
You must not use the identifier global_x for a different global in the same program, or you will get a collision. For this reason most people would call it something like hwconf_x.