Enhance views to [sometimes] support dynamic indexing and implement FlatIO (backport #2476) (#2479)

* Capture 1:1 mappings of Aggregates inside of views

This is implemented by including any corresponding Aggregates from the
DataView.mapping in the AggregateViewBinding.childMap (which is now of
type Map[Data, Data]).

This enables dynamically indexing Vecs that are themselves elements of
larger Aggregates in views when the corresponding element of the view is
a Vec of the same type. It also increases the number of cases where a
single Target can represent part of a view.

(cherry picked from commit 1f6b1ca14ccf86918065073c3f6f3626dd83a68e)

* Add FlatIO API for creating ports from Bundles without a prefix

(cherry picked from commit 772a3a1fe3b9372b7c2d7cd2d424b2adcd633cdb)

* [docs] Add FlatIO to the general cookbook

(cherry picked from commit b4159641350f238f0f899b69954142ce8ee11544)

Co-authored-by: Jack Koenig <koenig@sifive.com>

1 files changed, 45 insertions, 0 deletions

diff --git a/docs/src/cookbooks/cookbook.md b/docs/src/cookbooks/cookbook.md
index ae7c7bf6..b9e5db38 100644
--- a/docs/src/cookbooks/cookbook.md
+++ b/docs/src/cookbooks/cookbook.md
@@ -26,6 +26,7 @@ Please note that these examples make use of [Chisel's scala-style printing](../e
 * [How do I unpack a value ("reverse concatenation") like in Verilog?](#how-do-i-unpack-a-value-reverse-concatenation-like-in-verilog)
 * [How do I do subword assignment (assign to some bits in a UInt)?](#how-do-i-do-subword-assignment-assign-to-some-bits-in-a-uint)
 * [How do I create an optional I/O?](#how-do-i-create-an-optional-io)
+* [How do I create I/O without a prefix?](#how-do-i-create-io-without-a-prefix)
 * [How do I minimize the number of bits used in an output vector](#how-do-i-minimize-the-number-of-bits-used-in-an-output-vector)
 * Predictable Naming
   * [How do I get Chisel to name signals properly in blocks like when/withClockAndReset?](#how-do-i-get-chisel-to-name-signals-properly-in-blocks-like-whenwithclockandreset)
@@ -546,6 +547,50 @@ class ModuleWithOptionalIO(flag: Boolean) extends Module {
 }
 ```
 
+### How do I create I/O without a prefix?
+
+In most cases, you can simply call `IO` multiple times:
+
+```scala mdoc:silent:reset
+import chisel3._
+
+class MyModule extends Module {
+  val in = IO(Input(UInt(8.W)))
+  val out = IO(Output(UInt(8.W)))
+
+  out := in +% 1.U
+}
+```
+
+```scala mdoc:verilog
+getVerilogString(new MyModule)
+```
+
+If you have a `Bundle` from which you would like to create ports without the
+normal `val` prefix, you can use `FlatIO`:
+
+```scala mdoc:silent:reset
+import chisel3._
+import chisel3.experimental.FlatIO
+
+class MyBundle extends Bundle {
+  val foo = Input(UInt(8.W))
+  val bar = Output(UInt(8.W))
+}
+
+class MyModule extends Module {
+  val io = FlatIO(new MyBundle)
+
+  io.bar := io.foo +% 1.U
+}
+```
+
+Note that `io_` is nowhere to be seen!
+
+```scala mdoc:verilog
+getVerilogString(new MyModule)
+```
+
 ### How do I minimize the number of bits used in an output vector?
 
 Use inferred width and a `Seq` instead of a `Vec`: