Add support for selecting pin alternate functions from python.

Converts generted pins to use qstrs instead of string pointers.

This patch also adds the following functions:
pyb.Pin.names()
pyb.Pin.af_list()
pyb.Pin.gpio()

dir(pyb.Pin.board) and dir(pyb.Pin.cpu) also produce useful results.

pyb.Pin now takes kw args.

pyb.Pin.__str__ now prints more useful information about the pin
configuration.

I found the following functions in my boot.py to be useful:
```python
def pins():
    for pin_name in dir(pyb.Pin.board):
        pin = pyb.Pin(pin_name)
        print('{:10s} {:s}'.format(pin_name, str(pin)))

def af():
    for pin_name in dir(pyb.Pin.board):
        pin = pyb.Pin(pin_name)
        print('{:10s} {:s}'.format(pin_name, str(pin.af_list())))
```

2 files changed, 65 insertions, 4 deletions

diff --git a/stmhal/boards/make-pins.py b/stmhal/boards/make-pins.py
index e3a3f583a..f3d1dee48 100755
--- a/stmhal/boards/make-pins.py
+++ b/stmhal/boards/make-pins.py
@@ -72,6 +72,9 @@ class AlternateFunction(object):
             return self.func
         return '{:s}{:d}'.format(self.func, self.fn_num)
 
+    def mux_name(self):
+        return 'AF{:d}_{:s}'.format(self.idx, self.ptr())
+
     def print(self):
         """Prints the C representation of this AF."""
         if self.supported:
@@ -84,6 +87,9 @@ class AlternateFunction(object):
         print('({:2d}, {:8s}, {:2d}, {:10s}, {:8s}), // {:s}'.format(self.idx,
               self.func, fn_num, self.pin_type, self.ptr(), self.af_str))
 
+    def qstr_list(self):
+        return [self.mux_name()]
+
 
 class Pin(object):
     """Holds the information associated with a pin."""
@@ -170,6 +176,14 @@ class Pin(object):
             hdr_file.write('extern const pin_af_obj_t pin_{:s}_af[];\n'.
                            format(self.cpu_pin_name()))
 
+    def qstr_list(self):
+        result = []
+        for alt_fn in self.alt_fn:
+            if alt_fn.is_supported():
+                result += alt_fn.qstr_list()
+        return result
+
+
 class NamedPin(object):
 
     def __init__(self, name, pin):
@@ -225,13 +239,13 @@ class Pins(object):
                     self.board_pins.append(NamedPin(row[0], pin))
 
     def print_named(self, label, named_pins):
-        print('const pin_named_pin_t pin_{:s}_pins[] = {{'.format(label))
+        print('STATIC const mp_map_elem_t pin_{:s}_pins_locals_dict_table[] = {{'.format(label))
         for named_pin in named_pins:
             pin = named_pin.pin()
             if pin.is_board_pin():
-                print('  {{ "{:s}", &pin_{:s} }},'.format(named_pin.name(),  pin.cpu_pin_name()))
-        print('  { NULL, NULL }')
+                print('  {{ MP_OBJ_NEW_QSTR(MP_QSTR_{:s}), (mp_obj_t)&pin_{:s} }},'.format(named_pin.name(),  pin.cpu_pin_name()))
         print('};')
+        print('MP_DEFINE_CONST_DICT(pin_{:s}_pins_locals_dict, pin_{:s}_pins_locals_dict_table);'.format(label, label));
 
     def print(self):
         for named_pin in self.cpu_pins:
@@ -269,6 +283,38 @@ class Pins(object):
             hdr_file.write('extern const pin_obj_t * const pin_adc2[];\n')
             hdr_file.write('extern const pin_obj_t * const pin_adc3[];\n')
 
+    def print_qstr(self, qstr_filename):
+        with open(qstr_filename, 'wt') as qstr_file:
+            qstr_set = set([])
+            for named_pin in self.cpu_pins:
+                pin = named_pin.pin()
+                if pin.is_board_pin():
+                    qstr_set |= set(pin.qstr_list())
+                    qstr_set |= set([named_pin.name()])
+            for named_pin in self.board_pins:
+                qstr_set |= set([named_pin.name()])
+            for qstr in sorted(qstr_set):
+                print('Q({})'.format(qstr), file=qstr_file)
+
+    def print_af_hdr(self, af_const_filename):
+        with open(af_const_filename,  'wt') as af_const_file:
+            af_hdr_set = set([])
+            mux_name_width = 0
+            for named_pin in self.cpu_pins:
+                pin = named_pin.pin()
+                if pin.is_board_pin():
+                    for af in pin.alt_fn:
+                        if af.is_supported():
+                            mux_name = af.mux_name()
+                            af_hdr_set |= set([mux_name])
+                            if len(mux_name) > mux_name_width:
+                                mux_name_width = len(mux_name)
+            for mux_name in sorted(af_hdr_set):
+                key = 'MP_OBJ_NEW_QSTR(MP_QSTR_{}),'.format(mux_name)
+                val = 'MP_OBJ_NEW_SMALL_INT(GPIO_{})'.format(mux_name)
+                print('    { %-*s %s },' % (mux_name_width + 26, key, val),
+                      file=af_const_file)
+
 
 def main():
     parser = argparse.ArgumentParser(
@@ -283,6 +329,12 @@ def main():
         default="stm32f4xx-af.csv"
     )
     parser.add_argument(
+        "--af-const",
+        dest="af_const_filename",
+        help="Specifies header file for alternate function constants.",
+        default="build/pins-af-const.h"
+    )
+    parser.add_argument(
         "-b", "--board",
         dest="board_filename",
         help="Specifies the board file",
@@ -294,6 +346,12 @@ def main():
         default="stm32f4xx-prefix.c"
     )
     parser.add_argument(
+        "-q", "--qstr",
+        dest="qstr_filename",
+        help="Specifies name of generated qstr header file",
+        default="build/pins-qstr.h"
+    )
+    parser.add_argument(
         "-r", "--hdr",
         dest="hdr_filename",
         help="Specifies name of generated pin header file",
@@ -323,6 +381,8 @@ def main():
     pins.print_adc(2)
     pins.print_adc(3)
     pins.print_header(args.hdr_filename)
+    pins.print_qstr(args.qstr_filename)
+    pins.print_af_hdr(args.af_const_filename)
 
 
 if __name__ == "__main__":
diff --git a/stmhal/boards/stm32f4xx-prefix.c b/stmhal/boards/stm32f4xx-prefix.c
index 3bbb6bda0..45bcc0b65 100644
--- a/stmhal/boards/stm32f4xx-prefix.c
+++ b/stmhal/boards/stm32f4xx-prefix.c
@@ -14,6 +14,7 @@
 #define AF(af_idx, af_fn, af_unit, af_type, af_ptr) \
 { \
     { &pin_af_type }, \
+    .name = MP_QSTR_AF ## af_idx ## _ ## af_fn ## af_unit, \
     .idx = (af_idx), \
     .fn = AF_FN_ ## af_fn, \
     .unit = (af_unit), \
@@ -24,7 +25,7 @@
 #define PIN(p_port, p_pin, p_num_af, p_af, p_adc_num, p_adc_channel) \
 { \
     { &pin_type }, \
-    .name = #p_port #p_pin, \
+    .name = MP_QSTR_ ## p_port ## p_pin, \
     .port = PORT_ ## p_port, \
     .pin = (p_pin), \
     .num_af = (p_num_af), \