mp_obj_int_get_truncated is used as a "fast path" int accessor that
doesn't check for overflow and returns the int truncated to the machine
word size, ie mp_int_t.
Use mp_obj_int_get_truncated to fix struct.pack when packing maximum word
sized values.
Addresses issues #779 and #998.
Before, sizeof() could be applied to a structure field only if that field
was itself a structure. Now it can be applied to PTR and ARRAY fields too.
It's not possible to apply it to scalar fields though, because as soon as
scalar field (int or float) is dereferenced, its value is converted into
Python int/float value, and all original type info is lost. Moreover, we
allow sizeof of type definitions too, and there int is used to represent
(scalar) types. So, we have ambiguity what int may be - either dereferenced
scalar structure field, or encoded scalar type. So, rather throw an error
if user tries to apply sizeof() to int.
Teensy doesn't need to worry about overflows since all of
its timers are only 16-bit.
For PWM, the pulse width needs to be able to vary from 0..period+1
(pulse-width == period+1 corresponds to 100% PWM)
I couldn't test the 0xffffffff cases since we can't currently get a
period that big in python. With a prescaler of 0, that corresponds
to a freq of 0.039 (i.e. cycle every 25.56 seconds), and we can't
set that using freq or period.
I also tested both stmhal and teensy with floats disabled, which
required a few other code changes to compile.
