[Util] add comments to npy/rtlsim conv functions

src/finn/backend/fpgadataflow/utils.py

@@ -6,7 +6,7 @@ import numpy as np
 from finn.core.datatype import DataType
 from finn.core.utils import (
     pack_innermost_dim_as_hex_string,
-    unpack_innermost_dim_from_hex_string
+    unpack_innermost_dim_from_hex_string,
 )
 
 
@@ -63,6 +63,12 @@ def numpy_to_hls_code(
 
 
 def npy_to_rtlsim_input(input_file, input_dtype, pad_to_nbits):
+    """Convert the multidimensional NumPy array of integers (stored as floats)
+    from input_file into a flattened sequence of Python arbitrary-precision
+    integers, packing the innermost dimension. See
+    finn.core.utils.pack_innermost_dim_as_hex_string() for more info on how the
+    packing works."""
+
     inp = np.load(input_file)
     ishape = inp.shape
     inp = inp.flatten()
@@ -79,6 +85,11 @@ def npy_to_rtlsim_input(input_file, input_dtype, pad_to_nbits):
 
 
 def rtlsim_output_to_npy(output, path, dtype, shape, packedBits, targetBits):
+    """Convert a flattened sequence of Python arbitrary-precision integers
+    output into a NumPy array. Each arbitrary-precision integer is assumed to
+    be a packed array of targetBits-bit elements, which will be unpacked
+    as the innermost dimension of the NumPy array."""
+
     output = [hex(int(x)) for x in output]
     out_array = unpack_innermost_dim_from_hex_string(
         output, dtype, shape, packedBits, targetBits, True