return r[field_slice(msb0_start, msb0_end, field_width)]
-def sel(r, sel_bits, field_width=None):
- """Forms a subfield from a selection of bits of the signal `r`
- ("register").
-
- :param r: signal containing the field from which to select the subfield
- :param sel_bits: bit indices of the subfield, in "MSB 0" convention,
- from most significant to least significant. Note that
- the indices are allowed to be non-contiguous and
- out-of-order.
- :param field_width: field width. If absent, use the signal `r` own width.
- """
- # find the MSB index in LSB0 numbering
- if field_width is None:
- msb = len(r) - 1
- else:
- msb = field_width - 1
- # extract the selected bits
- sig_list = []
- for idx in sel_bits:
- sig_list.append(r[msb - idx])
- # place the LSB at the front of the list,
- # since, in nMigen, Cat starts from the LSB
- sig_list.reverse()
- return Cat(*sig_list)
-
-
# Listed in V3.0B Book III Chap 4.2.1
# MSR bit numbers, *bigendian* order (PowerISA format)
# use this in the simulator