make imports less ugly

If code outside our main entry point, e.g. our examples, wanted
to use the src_to_binary function, it needed an ugly import of
esp32_ulp.__main__. With this change the import becomes cleaner,
e.g. `from esp32_ulp import src_to_binary`.

The original "main" method, which took a filename as input and
resulted in a ULP binary file as output, is now also more cleanly
available as assemble_file() inside the esp32_ulp module.

Fixes #39.

Author: wnienhaus

esp32_ulp/__init__.py

@@ -0,0 +1,32 @@
+from .util import garbage_collect
+
+from .preprocess import preprocess
+from .assemble import Assembler
+from .link import make_binary
+garbage_collect('after import')
+
+
+def src_to_binary(src):
+    assembler = Assembler()
+    src = preprocess(src)
+    assembler.assemble(src, remove_comments=False)  # comments already removed by preprocessor
+    garbage_collect('before symbols export')
+    addrs_syms = assembler.symbols.export()
+    for addr, sym in addrs_syms:
+        print('%04d %s' % (addr, sym))
+
+    text, data, bss_len = assembler.fetch()
+    return make_binary(text, data, bss_len)
+
+
+def assemble_file(filename):
+    with open(filename) as f:
+        src = f.read()
+
+    binary = src_to_binary(src)
+
+    if filename.endswith('.s') or filename.endswith('.S'):
+        filename = filename[:-2]
+    with open(filename + '.ulp', 'wb') as f:
+        f.write(binary)
+

esp32_ulp/__main__.py

@@ -1,36 +1,9 @@
 import sys
-
-from .util import garbage_collect
-
-from .preprocess import preprocess
-from .assemble import Assembler
-from .link import make_binary
-garbage_collect('after import')
-
-
-def src_to_binary(src):
-    assembler = Assembler()
-    src = preprocess(src)
-    assembler.assemble(src, remove_comments=False)  # comments already removed by preprocessor
-    garbage_collect('before symbols export')
-    addrs_syms = assembler.symbols.export()
-    for addr, sym in addrs_syms:
-        print('%04d %s' % (addr, sym))
-
-    text, data, bss_len = assembler.fetch()
-    return make_binary(text, data, bss_len)
+from . import assemble_file
 
 
 def main(fn):
-    with open(fn) as f:
-        src = f.read()
-
-    binary = src_to_binary(src)
-
-    if fn.endswith('.s') or fn.endswith('.S'):
-        fn = fn[:-2]
-    with open(fn + '.ulp', 'wb') as f:
-        f.write(binary)
+    assemble_file(fn)
 
 
 if __name__ == '__main__':

examples/counter.py

@@ -12,7 +12,7 @@
 from esp32 import ULP
 from machine import mem32
 
-from esp32_ulp.__main__ import src_to_binary
+from esp32_ulp import src_to_binary
 
 source = """\
 data:       .long 0