1 # PartitionedSignal nmigen-aware eq (assign)
3 * <https://bugs.libre-soc.org/show_bug.cgi?id=709>
5 For copying (assigning) PartitionedSignal to PartitionedSignal
6 of equal size there is no issue. However if the source has a
7 greater width than the target, *partition-aware* truncation
8 must occur. For the opposite, sign/zero extension must occur.
9 Finally for a Signal or Const, duplication across all Partitions
10 must occur, again, following the rules of zero, sign or unsigned.
12 Take two PartitionedSignals (source a, dest b) of 32 bit:
14 partition: p p p (3 bits)
15 a : AAA3 AAA2 AAA1 AAA0 (32 bits)
16 b : BBB3 BBB2 BBB1 BBB0 (32 bits)
18 For all partition settings this copies verbatim. Also,
19 when A is longer, a truncated version of A is always
20 copied verbatim, regardless of partition settings.
24 partition: p p p (3 bits)
25 a : A7A6 A5A4 A3A2 A1A0 (8 bits)
26 b : BBB3 BBB2 BBB1 BBB0 (16 bits)
28 then it matters what the partition settings are:
30 | partition | o3 | o2 | o1 | o0 |
31 | --------- | -- | -- | -- | -- |
32 | 000 | [A7A7A7A7] | [A7A7A7A7] | A7A6A5A4 | A3A2A1A0 |
33 | 001 | [A7A7A7A7] | [A7A7]A7A6 | A5A4A3A2 | [A1A1]A1A0 |
34 | 010 | [A7A7A7A7] | A7A6A5A4 | [A3A3A3A3] | A3A2A1A0 |
35 | 011 | [A7A7A7A7] | A7A6A5A4 | [A3A3]A3A2 | [A1A1]A1A0 |
36 | 100 | [A7A7]A7A6 | [A5A5A5A5] | [A5A5]A5A4 | A3A2A1A0 |
37 | 101 | [A7A7]A7A6 | [A5A5A5A5] | A5A4A3A2 | [A1A1]A1A0 |
38 | 110 | [A7A7]A7A6 | [A5A5]A5A4 | [A3A3A3A3] | A3A2A1A0 |
39 | 111 | [A7A7]A7A6 | [A5A5]A5A4 | [A3A3]A3A2 | [A1A1]A1A0 |
41 where square brackets are zero if A is unsigned, and contains
42 the specified bits if signed. Here, each partition copies the
43 smaller value (A) into the larger partition (B) then, depending
44 on whether A is signed or unsigned, sign-extends or zero-extends
45 *on a per-partition basis*.
47 When the source A is scalar and is equal or larger than
48 the destination it requires copying across multiple
51 partition: p p p (3 bits)
52 a : AAAA AAAA AAAA AAAA (16 bits)
53 b : B7B6 B5B4 B3B2 B1B0 (8 bits)
55 The partition options are:
57 | partition | o3 | o2 | o1 | o0 |
58 | --------- | -- | -- | -- | -- |
59 | 000 | A7A6 | A5A4 | A3A2 | A1A0 |
60 | 001 | A5A4 | A3A2 | A1A0 | A1A0 |
61 | 010 | A3A2 | A1A0 | A3A2 | A1A0 |
62 | 100 | A1A0 | A5A4 | A3A2 | A1A0 |
63 | 111 | A1A0 | A1A0 | A1A0 | A1A0 |