From 5f19697618b7f42e4c0df54bfc9a4030c83b4f01 Mon Sep 17 00:00:00 2001 From: abejgonzalez Date: Fri, 31 May 2019 17:51:05 -0700 Subject: [PATCH] first attempt at explaining heter systems --- docs/Advanced-Usage/Heterogeneous-SoCs.rst | 127 +++++++++++++++++++++ docs/Advanced-Usage/index.rst | 11 ++ docs/index.rst | 4 + 3 files changed, 142 insertions(+) create mode 100644 docs/Advanced-Usage/Heterogeneous-SoCs.rst create mode 100644 docs/Advanced-Usage/index.rst diff --git a/docs/Advanced-Usage/Heterogeneous-SoCs.rst b/docs/Advanced-Usage/Heterogeneous-SoCs.rst new file mode 100644 index 00000000..2ee9cba4 --- /dev/null +++ b/docs/Advanced-Usage/Heterogeneous-SoCs.rst @@ -0,0 +1,127 @@ +Heterogeneous SoCs +=============================== + +The REBAR framework involves multiple cores and accelerators that can be composed in arbitrary ways. +This discussion will focus on how you combine Rocket, BOOM and Hwacha in particular ways to create a unique SoC. + +Creating a Rocket and BOOM System +------------------------------------------- + +Instantiating an SoC with Rocket and BOOM cores is all done with the configuration system and two specific mixins. +Both BOOM and Rocket have mixins labelled ``WithNBoomCores(X)`` and ``WithNBigCores(X)`` that automatically create ``X`` copies of the core. +When used together you can create a heterogeneous system. +The following example shows a dual core BOOM with a single Rocket. + +.. code-block:: scala + + class DualCoreBoomAndRocketConfig extends Config( + new WithNormalBoomRocketTop ++ + new WithBootROM ++ + new boom.system.WithRenumberHarts ++ + new boom.common.WithRVC ++ + new boom.common.DefaultBoomConfig ++ + new boom.system.WithNBoomCores(2) ++ + new freechips.rocketchip.subsystem.WithoutTLMonitors ++ + new freechips.rocketchip.subsystem.WithNBigCores(1) ++ + new freechips.rocketchip.system.BaseConfig) + +In this example, the ``WithN...Cores(X)`` mixins set up particular parameters for the duplicated core. +For example, the Rocket tiles will be "BigCores" while BOOM has some generic parameters set in its mixin. +In BOOMs case, we override these base core parameters to create multiple "DefaultBoom"s with calling ``DefaultBoomConfig`` after the multi-core instantiation. +This mixin applies to all the BOOM cores in the system and sets up the parameters for each. + +Great! Now you have a heterogeneous setup with BOOMs and Rockets. +The final thing you need to make this system work is to renumber the ``hartId``'s of the cores so that each core has a unique ``hartId``. +This is done with ``WithRenumberHarts`` (which can label the Rocket cores first or the BOOM cores first). +The reason this is needed is because by default the ``WithN...Cores(X)`` mixin assumes that there are only that type of core in the system. +Thus, without the renumber mixin, each set of cores is labeled starting from zero. + +Another option to create a multi heterogeneous core system is to override the parameters yourself so you can specify the core parameters per core. +The mixin to add to your system would look something like the following. + +.. code-block:: scala + + // create 6 cores (4 boom and 2 rocket) + class WithHeterCoresSetup extends Config((site, here, up) => { + case BoomTilesKey => { + val boomTile0 = BoomTileParams(...) // params for boom core 0 + val boomTile1 = BoomTileParams(...) // params for boom core 1 + val boomTile2 = BoomTileParams(...) // params for boom core 2 + val boomTile3 = BoomTileParams(...) // params for boom core 3 + boomTile0 ++ boomTile1 ++ boomTile2 ++ boomTile3 + } + + case RocketTilesKey => { + val rocketTile0 = RocketTileParams(...) // params for rocket core 0 + val rocketTile1 = RocketTileParams(...) // params for rocket core 1 + rocketTile0 ++ rocketTile1 + } + }) + +Then you could use this new mixin like the following. + +.. code-block:: scala + + class SixCoreConfig extends Config( + new WithNormalBoomRocketTop ++ + new WithBootROM ++ + new WithHeterCoresSetup ++ + new freechips.rocketchip.system.BaseConfig) + +Note, in this setup you most likely dont need the ``WithRenumberHarts`` mixin since you have to assign the ``hartId`` of each tile in the params yourself. + +Adding Hwachas +------------------------------------------- + +Adding a Hwacha accelerator is as easy as adding the ``DefaultHwachaConfig`` so that it can setup the Hwacha parameters and add itself to the ``BuildRoCC`` parameter. +An example of adding a Hwacha to all tiles in the system is below. + +.. code-block:: scala + + class DualCoreBoomAndRocketWithHwachasConfig extends Config( + new WithNormalBoomRocketTop ++ + new WithBootROM ++ + new hwacha.DefaultHwachaConfig ++ + new boom.system.WithRenumberHarts ++ + new boom.common.WithRVC ++ + new boom.common.DefaultBoomConfig ++ + new boom.system.WithNBoomCores(2) ++ + new freechips.rocketchip.subsystem.WithoutTLMonitors ++ + new freechips.rocketchip.subsystem.WithNBigCores(1) ++ + new freechips.rocketchip.system.BaseConfig) + +In this example, Hwachas are added to both BOOM's and to the Rocket tile. +All with the same Hwacha parameters. + +Assigning Accelerators to Specific Tiles with MultiRoCC +------------------------------------------------------- + +Located in ``generators/example/src/main/scala/ConfigMixins.scala`` is a Mixin that provides support for adding RoCC accelerators to specific tiles in your SoC. +Named ``MultiRoCCKey``, this key allows you to attach RoCC accelerators based on the ``hartId`` of the tile. +For example, using this allows you to create a 8 tile system with a RoCC accelerator on only a subset of the tiles. +An example is shown below with two BOOM cores, and one Rocket attached to a Hwacha. + +.. code-block:: scala + + class DualCoreBoomAndOneHwachaRocketConfig extends Config( + new WithNormalBoomRocketTop ++ + new WithBootROM ++ + new WithMultiRoCC ++ + new WithMultiRoCCHwacha(0) ++ // put Hwacha just on hart0 which was renumbered to Rocket + new boom.system.WithRenumberHarts ++ + new hwacha.DefaultHwachaConfig ++ + new boom.common.WithRVC ++ + new boom.common.DefaultBoomConfig ++ + new boom.system.WithNBoomCores(2) ++ + new freechips.rocketchip.subsystem.WithoutTLMonitors ++ + new freechips.rocketchip.subsystem.WithNBigCores(1) ++ + new freechips.rocketchip.system.BaseConfig) + +In this example, the ``WithRenumberHarts`` relabels the ``hartId``'s of all the BOOM/Rocket cores. +Then after that is applied to the parameters, the ``WithMultiRoCCHwacha(0)`` is used to assign to ``hartId`` zero a Hwacha (in this case ``hartId`` zero is Rocket). +Finally, the ``WithMultiRoCC`` mixin is called. +This mixin sets the ``BuildRoCC`` key to use the ``MultiRoCCKey`` instead of the default. +This must be used after all the RoCC parameters are set because it needs to override the ``BuildRoCC`` parameter. +If this is used earlier in the configuration sequence, then MultiRoCC does not work. + +This mixin can be changed to put more accelerators on more cores by changing the arguments to cover more ``hartId``'s (i.e. ``WithMultiRoCCHwacha(0,1,3,6,...)``). diff --git a/docs/Advanced-Usage/index.rst b/docs/Advanced-Usage/index.rst new file mode 100644 index 00000000..6aa2a195 --- /dev/null +++ b/docs/Advanced-Usage/index.rst @@ -0,0 +1,11 @@ +Advanced Usage +================================ + +The following sections are advanced topics about how to use REBAR and special features of the framework. +They expect you to know about Chisel, Parameters, Configs, etc. + +.. toctree:: + :maxdepth: 2 + :caption: Getting Started: + + Heterogeneous-SoCs diff --git a/docs/index.rst b/docs/index.rst index ce083f2c..019a6991 100644 --- a/docs/index.rst +++ b/docs/index.rst @@ -37,6 +37,10 @@ New to Chipyard? Jump to the :ref:`Getting Started` page for more info. :numbered: VLSI/index + :maxdepth: 3 + :caption: Advanced Usage: + :numbered: + Advanced-Usage/index Indices and tables ==================