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fix README documentation for RoCC accelerators

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This commit is contained in:
Howard Mao
2019-02-15 15:30:22 -08:00
parent 51ca3dd1b9
commit e5cbf49bb4
1 changed files with 16 additions and 15 deletions
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31
README.md
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@@ -320,11 +320,13 @@ RoCC accelerators are lazy modules that extend the LazyRoCC class.
Their implementation should extends the LazyRoCCModule class.
```scala
class CustomAccelerator(implicit p: Parameters) extends LazyRoCC {
class CustomAccelerator(opcodes: OpcodeSet)
(implicit p: Parameters) extends LazyRoCC(opcodes) {
override lazy val module = new CustomAcceleratorModule(this)
}
class CustomAcceleratorModule(outer: CustomAccelerator) extends LazyRoCCModule(outer) {
class CustomAcceleratorModule(outer: CustomAccelerator)
extends LazyRoCCModuleImp(outer) {
val cmd = Queue(io.cmd)
// The parts of the command are as follows
// inst - the parts of the instruction itself
@@ -342,7 +344,11 @@ Their implementation should extends the LazyRoCCModule class.
}
```
The LazyRoCC class contains two TLOutputNode instances, `atlNode` and `tlNode`.
The `opcodes` parameter for `LazyRoCC` is
the set of custom opcodes that will map to this accelerator. More on this
in the next subsection.
The `LazyRoCC` class contains two TLOutputNode instances, `atlNode` and `tlNode`.
The former connects into a tile-local arbiter along with the backside of the
L1 instruction cache. The latter connects directly to the L1-L2 crossbar.
The corresponding Tilelink ports in the module implementation's IO bundle
@@ -358,26 +364,21 @@ detailed information on the different IOs.
### Adding RoCC accelerator to Config
RoCC accelerators can be added to a core by overriding the BuildRoCC parameter
in the configuration. This takes a sequence of RoccParameters objects, one
for each accelerator you wish to add. The two required fields for this
object are `opcodes` which determines which custom opcodes get routed to the
accelerator, and `generator` which specifies how to build the accelerator itself.
RoCC accelerators can be added to a core by overriding the `BuildRoCC` parameter
in the configuration. This takes a sequence of functions producing `LazyRoCC`
objects, one for each accelerator you wish to add.
For instance, if we wanted to add the previously defined accelerator and
route custom0 and custom1 instructions to it, we could do the following.
```scala
class WithCustomAccelerator extends Config((site, here, up) => {
case RocketTilesKey => up(RocketTilesKey, site).map { r =>
r.copy(rocc = Seq(
RoCCParams(
opcodes = OpcodeSet.custom0 | OpcodeSet.custom1,
generator = (p: Parameters) => LazyModule(new CustomAccelerator()(p)))))
}
case BuildRoCC => Seq((p: Parameters) => LazyModule(
new CustomAccelerator(OpcodeSet.custom0 | OpcodeSet.custom1)(p)))
})
class CustomAcceleratorConfig extends Config(
new WithCustomAccelerator ++ new BaseConfig)
new WithCustomAccelerator ++ new DefaultExampleConfig)
```
## Adding a submodule