diff --git a/esp32_ulp/__init__.py b/esp32_ulp/__init__.py
index 634605d..e14cca3 100644
--- a/esp32_ulp/__init__.py
+++ b/esp32_ulp/__init__.py
@@ -13,17 +13,21 @@
 garbage_collect('after import')
 
 
-def src_to_binary(src, cpu):
+def src_to_binary_ext(src, cpu):
     assembler = Assembler(cpu)
     src = preprocess(src)
     assembler.assemble(src, remove_comments=False)  # comments already removed by preprocessor
     garbage_collect('before symbols export')
     addrs_syms = assembler.symbols.export()
+    text, data, bss_len = assembler.fetch()
+    return make_binary(text, data, bss_len), addrs_syms
+
+
+def src_to_binary(src, cpu):
+    binary, addrs_syms = src_to_binary_ext(src, cpu)
     for addr, sym in addrs_syms:
         print('%04d %s' % (addr, sym))
-
-    text, data, bss_len = assembler.fetch()
-    return make_binary(text, data, bss_len)
+    return binary
 
 
 def assemble_file(filename, cpu):