diff options
| author | Schuyler Eldridge | 2021-08-02 16:35:00 -0400 |
|---|---|---|
| committer | GitHub | 2021-08-02 20:35:00 +0000 |
| commit | ff1cd28202fb423956a6803a889c3632487d8872 (patch) | |
| tree | 80067c965e2b8255474fe57b11c2f4ab7dc688fc | |
| parent | 04210ee30acd437bccfe694ddd895e5f450ba01f (diff) | |
Update spec to disallow 0-bit mux sel (#2305)
Change the FIRRTL spec to disallow a zero-width multiplexer select.
Clarify that the select line can be either one-bit or zero-bit, but will
infer to one-bit.
Signed-off-by: Schuyler Eldridge <schuyler.eldridge@sifive.com>
Co-authored-by: mergify[bot] <37929162+mergify[bot]@users.noreply.github.com>
| -rw-r--r-- | spec/spec.pdf | bin | 363498 -> 339523 bytes | |||
| -rw-r--r-- | spec/spec.tex | 3 |
2 files changed, 1 insertions, 2 deletions
diff --git a/spec/spec.pdf b/spec/spec.pdf Binary files differindex d961a28d..b92c62e3 100644 --- a/spec/spec.pdf +++ b/spec/spec.pdf diff --git a/spec/spec.tex b/spec/spec.tex index d41d0562..a876aca9 100644 --- a/spec/spec.tex +++ b/spec/spec.tex @@ -1307,9 +1307,8 @@ A multiplexer expression is legal only if the following holds. \item The type of the selection signal is an unsigned integer. \item The width of the selection signal is any of: \begin{enumerate} - \item Unspecified - \item Zero-bit\footnote{A zero-bit width selection signal will be treated as a one-bit, zero-valued selection signal. \emph{This means that a multiplexer expression with a zero-bit selection signal will always take the false path and will likely be optimized away by a FIRRTL compiler.}} \item One-bit + \item Unspecified, but will infer to one-bit \end{enumerate} \item The types of the two input expressions are equivalent. \item The types of the two input expressions are passive (see section \ref{passive_types}). |