add special handling for the BIT macro used in the esp-idf framework

The functions the preprocessor supports (WRITE_RTC_*/READ_RTC_*) do not need the
value returned by the BIT macro. Instead, they use the bit number specified to the
BIT macro, i.e. for BIT(x) they need x. So this change handles BIT by simply
replacing it with an empty string, and BIT(x) results in (x) in the preprocessor
output.

Author: wnienhaus

esp32_ulp/preprocess.py

@@ -70,6 +70,15 @@ def expand_defines(self, line):
                 lu = self._defines.get(t, t)
                 if lu == t and self._defines_db:
                     lu = self._defines_db.get(t, t)
+                if lu == t and t == 'BIT':
+                    # Special hack: BIT(..) translates to a 32-bit mask where only the specified bit is set.
+                    # But the reg_wr and reg_rd opcodes expect actual bit numbers for argument 2 and 3.
+                    # While the real READ_RTC_*/WRITE_RTC_* macros take in the output of BIT(x), they
+                    # ultimately convert these back (via helper macros) to the bit number (x). And since this
+                    # preprocessor does not (aim to) implement "proper" macro-processing, we can simply
+                    # short-circuit this round-trip via macros and replace "BIT" with nothing so that
+                    # "BIT(x)" gets mapped to "(x)".
+                    continue
                 if lu != t:
                     found = True
                 line += lu

tests/preprocess.py

@@ -185,6 +185,21 @@ def test_expand_rtc_macros():
     assert p.expand_rtc_macros("READ_RTC_FIELD(1, 2)") == "\treg_rd 1, 2 + 1 - 1, 2"
 
 
+@test
+def preprocess_should_replace_BIT_with_empty_string_unless_defined():
+    # by default replace BIT with empty string (see description for why in the code)
+    src = " move r1, 0x123 << BIT(24)"
+    assert "move r1, 0x123 << (24)" in Preprocessor().preprocess(src)
+
+    # but if BIT is defined, use that
+    src = """\
+    #define BIT 12
+
+    move r1, BIT"""
+
+    assert "move r1, 12" in Preprocessor().preprocess(src)
+
+
 @test
 def test_process_include_file():
     p = Preprocessor()