<<<
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== Software Toolchain Setup

To compile (and debug) executables for the NEORV32 a RISC-V toolchain is required.
There are two possibilities to get this:

1. Download and _build_ the official RISC-V GNU toolchain yourself.
2. Download and install a prebuilt version of the toolchain; this might also done via the package manager / app store of your OS

[NOTE]
The default toolchain prefix (`RISCV_PREFIX` variable) for this project is **`riscv32-unknown-elf-`**. Of course you can use any other RISC-V
toolchain (like `riscv64-unknown-elf-`) that is capable to emit code for a `rv32` architecture. Just change `RISCV_PREFIX`
according to your needs.


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=== Building the Toolchain from Scratch

To build the toolchain by yourself you can follow the guide from the official https://github.com/riscv-collab/riscv-gnu-toolchain GitHub page.
You need to make sure the generated toolchain fits the architecture of the NEORV32 core. To get a toolchain that even supports minimal
ISA extension configurations, it is recommend to compile for `rv32i` only. Please note that this minimal ISA also provides further ISA
extensions like `m` or `c`. Of course you can use a _multilib_ approach to generate toolchains for several target ISAs at once.

.Configuring GCC build for `rv32i` (minimal ISA)
[source,bash]
----
riscv-gnu-toolchain$ ./configure --prefix=/opt/riscv --with-arch=rv32i --with-abi=ilp32
riscv-gnu-toolchain$ make
----

[IMPORTANT]
Keep in mind that - for instance - a toolchain build with `--with-arch=rv32imc` only provides library code compiled with
compressed (`C`) and `mul`/`div` instructions (`M`)! Hence, this code cannot be executed (without
emulation) on an architecture without these extensions!

[IMPORTANT]
Make sure to use "newlib" as C standard library as the NEORV32 has no native support for Linus-like operating systems.


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=== Downloading and Installing a Prebuilt Toolchain

Alternatively, you can download a prebuilt toolchain.

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==== Use The Toolchain I have Build

I have compiled a GCC toolchain on a 64-bit x86 Ubuntu (Ubuntu on Windows, actually) and uploaded it to
GitHub. You can directly download the according toolchain archive as single _zip-file_ within a packed
release from https://github.com/stnolting/riscv-gcc-prebuilt.

Unpack the downloaded toolchain archive and copy the content to a location in your file system (e.g.
`/opt/riscv`). More information about downloading and installing my prebuilt toolchains can be found in
the repository's README.


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==== Use a Third Party Toolchain

Of course you can also use any other prebuilt version of the toolchain. There are a lot  RISC-V GCC packages out there -
even for Windows. On Linux system you might even be able to fetch a toolchain via your distribution's package manager.

[IMPORTANT]
Make sure the toolchain can (also) emit code for a `rv32i` architecture, uses the `ilp32` or `ilp32e` ABI and **was not build** using
CPU extensions that are not supported by the NEORV32 (like `D`).


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=== Installation

Now you have the toolchain binaries. The last step is to add them to your `PATH` environment variable (if you have not
already done so): make sure to add the _binaries_ folder (`bin`) of your toolchain.

[source,bash]
----
$ export PATH=$PATH:/opt/riscv/bin
----

You should add this command to your `.bashrc` (if you are using bash) to automatically add the RISC-V
toolchain at every console start.

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=== Testing the Installation

To make sure everything works fine, navigate to an example project in the NEORV32 example folder and
execute the following command:

[source,bash]
----
neorv32/sw/example/blink_led$ make check
----

This will test all the tools required for generating NEORV32 executables.
Everything is working fine if `Toolchain check OK` appears at the end.
