docs: recommend Sifive August 2020 toolchain

This gives us GCC 10.1 which produces faster code than 8.x. We can't use
the Sifive release of GCC 10.2 because it doesn't include rv32im.

Signed-off-by: Dan Callaghan <dcallagh@google.com>

docs/source/setup-guide.rst

@@ -35,19 +35,19 @@ Step 2: Install Vivado and Renode
 Step 3: Install RISCV toolchain
 -------------------------------
 
-1. Download the `April 2020`_ toolchain from freedom-tools and unpack the binaries to your home directory:
+1. Download the `August 2020`_ toolchain from freedom-tools and unpack the binaries to your home directory:
 
-.. _`April 2020`: https://github.com/sifive/freedom-tools/releases/tag/v2020.04.0-Toolchain.Only
+.. _`August 2020`: https://github.com/sifive/freedom-tools/releases/tag/v2020.08.0
 
 .. code-block:: bash
 
-   $ tar xvfz ~/Downloads/riscv64-unknown-elf-gcc-8.3.0-2020.04.1-x86_64-linux-ubuntu14.tar.gz
+   $ tar xvfz ~/Downloads/riscv64-unknown-elf-gcc-10.1.0-2020.08.2-x86_64-linux-ubuntu14.tar.gz
 
 2. Add the toolchain to your `PATH` in your ``.bashrc`` script:
 
 .. code-block:: bash
 
-   export PATH=$PATH:$HOME/riscv64-unknown-elf-gcc-8.3.0-2020.04.1-x86_64-linux-ubuntu14/bin
+   export PATH=$PATH:$HOME/riscv64-unknown-elf-gcc-10.1.0-2020.08.2-x86_64-linux-ubuntu14/bin
 
 
 Step 4: Clone the CFU-Playground Repository

scripts/setup

@@ -118,8 +118,8 @@ if ! which riscv64-unknown-elf-gcc >/dev/null; then
     echo "Error: RISCV GCC toolchain not found. Please install one, following the instructions at"
     echo "https://cfu-playground.readthedocs.io/en/latest/setup-guide.html#step-3-install-riscv-toolchain"
 
-elif ! riscv64-unknown-elf-gcc --version | grep 'SiFive GCC 8.3.0-2020.04.1.' >/dev/null; then
-    echo "Unsupported version of riscv64-unknown-elf-gcc. SiFive GCC 8.3.0-2020.04.1 is known to work." >&2
+elif ! riscv64-unknown-elf-gcc --version | grep 'SiFive GCC 10.1.' >/dev/null; then
+    echo "Unsupported version of riscv64-unknown-elf-gcc. SiFive GCC 10.1.0 is known to work." >&2
     echo "To install this version, follow the instructions at"
     echo "https://cfu-playground.readthedocs.io/en/latest/setup-guide.html#step-3-install-riscv-toolchain"
 fi