py/viper: Allow casting of Python integers to viper pointers.

This allows you to pass a number (being an address) to a viper function
that expects a pointer, and also allows casting of integers to pointers
within viper functions.

This was actually the original behaviour, but it regressed due to native
type identifiers being promoted to 4 bits in width.

py/nativeglue.c

@@ -50,10 +50,14 @@ mp_uint_t mp_convert_obj_to_native(mp_obj_t obj, mp_uint_t type) {
         case MP_NATIVE_TYPE_BOOL:
         case MP_NATIVE_TYPE_INT:
         case MP_NATIVE_TYPE_UINT: return mp_obj_get_int_truncated(obj);
-        default: { // a pointer
+        default: { // cast obj to a pointer
             mp_buffer_info_t bufinfo;
-            mp_get_buffer_raise(obj, &bufinfo, MP_BUFFER_RW);
+            if (mp_get_buffer(obj, &bufinfo, MP_BUFFER_RW)) {
                 return (mp_uint_t)bufinfo.buf;
+            } else {
+                // assume obj is an integer that represents an address
+                return mp_obj_get_int_truncated(obj);
+            }
         }
     }
 }

tests/micropython/viper_addr.py

+# test passing addresses to viper
+
+@micropython.viper
+def get_addr(x:ptr) -> ptr:
+    return x
+
+@micropython.viper
+def memset(dest:ptr8, c:int, n:int):
+    for i in range(n):
+        dest[i] = c
+
+# create array and get its address
+ar = bytearray('0000')
+addr = get_addr(ar)
+print(type(ar))
+print(type(addr))
+print(ar)
+
+# pass array as an object
+memset(ar, ord('1'), len(ar))
+print(ar)
+
+# pass direct pointer to array buffer
+memset(addr, ord('2'), len(ar))
+print(ar)
+
+# pass direct pointer to array buffer, with offset
+memset(addr + 2, ord('3'), len(ar) - 2)
+print(ar)

tests/micropython/viper_addr.py.exp

+<class 'bytearray'>
+<class 'int'>
+bytearray(b'0000')
+bytearray(b'1111')
+bytearray(b'2222')
+bytearray(b'2233')