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Cross-compiling ScummVM on for Raspberry Pi

Installing the official Raspberry Pi cross-compiler on PC

We will clone the Raspberry Pi tools repository which includes the cross-compiler we need:

git clone https://github.com/raspberrypi/tools.git

It will get cloned to a directory called tools at our current location.

Add it to the PATH environment variable so that we have the cross-compiler binaries available from our ScummVM building directory. For example, if the Raspberry Pi tools repository was cloned in tools under our user's home directory, we would do:

export PATH=$PATH:$HOME/tools/arm-bcm2708/arm-linux-gnueabihf/bin

After adding the cross-compiler executables directory to PATH, we should be able to run arm-linux-gnueabihf-gcc, arm-linux-gnueabihf-g++, etc. They should yield an error because we pass them no input files, but that's expected. This is just a test so we know we have the cross-compiler installed and accessible.

Installing the needed Raspberry Pi headers and libraries on PC

We need to copy over the /usr, /lib and /opt directories from the Raspbian SD Card to the host PC (the computer where we will do the cross-compilation) for the needed headers and libraries to be available.

Of course, first we'll have to install any additional libraries from Raspbian running on the Pi before expecting them to be available so, eg. if we want to compile ScummVM with FLAC support, we should have installed the libflac development libraries on the Pi in advance.

As an example, on the Raspberry Pi running Raspbian (Buster) OS 3.2 (January 2020) we can execute the following to install third party libraries that ScummVM needs for its features and various game engines:

sudo apt-get update
sudo apt-get upgrade
sudo apt-get install -y --no-install-recommends \
             libsdl2-dev \
             liba52-0.7.4-dev \
             libjpeg62-turbo-dev \
             libmpeg2-4-dev \
             libogg-dev \
             libvorbis-dev \
             libflac-dev \
             libmad0-dev \
             libpng-dev \
             libtheora-dev \
             libfaad-dev \
             libfluidsynth-dev \
             libfreetype6-dev \
             libcurl4-openssl-dev  \
             libsdl2-net-dev \
             libspeechd-dev \
             zlib1g-dev

On the host PC we first export the path where we will copy these into, and then we manually copy them. One option (shown in the example commands below) is to copy the Raspberry Pi headers and libraries to /opt/rpi_root, but any other path with the right permissions for our user (within common sense) should be ok:

mkdir -p /opt/rpi_root
export RPI_ROOT=/opt/rpi_root
cd <Raspbian_SD_card_mountpoint_directory>
cp -R usr lib opt $RPI_ROOT

The above copying of files has the unfortunate side-effect that many symbolic links that were copied over are now invalid, particularly those linking to absolute paths. Fortunately, we can remedy this situation by downloading and running a python script that will fix those links:

wget https://raw.githubusercontent.com/riscv/riscv-poky/master/scripts/sysroot-relativelinks.py
chmod +x sysroot-relativelinks.py
./sysroot-relativelinks.py $RPI_ROOT

Finally, update the PATH variable to be preceded by the RPI_ROOT path, since this is required for proper detection of libcurl related files by ScummVM's configure script.

export PATH=$RPI_ROOT:$PATH

Configuring ScummVM

First, we should make sure have the latest version of the ScummVM code locally (using git clone or git pull appropriately).

Then, navigate inside the local scummvm source code folder.

Now we can configure the ScummVM build system so it knows what backend we target and where our Raspberry Pi local sysroot is located, containing the Raspberry Pi headers and libraries the cross-compiler and linker will need. In this example configuration, we disable debug symbols since it's intended for final users.

PKG_CONFIG_SYSROOT_DIR=$RPI_ROOT PKG_CONFIG_LIBDIR=$RPI_ROOT/usr/lib/arm-linux-gnueabihf/pkgconfig ./configure --host=raspberrypi --with-sdl-prefix=$RPI_ROOT/usr --with-png-prefix=$RPI_ROOT/usr --disable-debug --enable-release

Remember that we have already exported the RPI_ROOT environment variable previously and updated the PATH environment variable to be preceded by the RPI_ROOT path and succeeded by the path to the Raspberry Pi toolchain bin folder (as shown in the previous steps).

On the Raspberry Pi, SDL2 will always be used, since it provides graphics acceleration.

Unfortunately, the official toolchain for cross-compiling for Pi is, as of yet, using an old gcc version (4.3.9) and hence, the configure script may fail to detect the FluidSynth library specifically. FluidSynth and MT-32 emulation are features that are very demanding on CPU processing power so it should be ok to skip them entirely. Alternatively, one could seek out a more up-to-date armhf toolchain for the cross-compilation, such as this Raspberry Pi toolchain by Stefan Profanter (Pro) which, in its 1.0.1 version, uses gcc version 8.3.0 and reportedly "supports all new Raspberry PIs (ARMv7), and the older ones, including Zero, A, B, B+ (ARMv6) with newer GCCs."

Note 1: If installing the Raspberry Pi toolchain by Stefan Profanter (Pro), it's important to read the instructions from the README file (also available from the main page of the repository). Specifically, this toolchain needs to be installed in /opt/cross-pi-gcc since it's not location independent.

Note 2: If building ScummVM directly on the Raspberry Pi / Raspbian itself, it's possible to run out of memory during the final linking process of the build. If GNU ld is used for compiling, then execute the following before running configure:

export LDFLAGS="-Wl,--no-keep-memory"

This tells GNU ld to optimize the linking for memory usage.

Compiling ScummVM

Provided that the configure step was executed successfully, we can proceed to run the following commands in order to build ScummVM:

make clean
make -j$(nproc)

Installing ScummVM on the Raspberry Pi

In this step we simply have to copy over the resulting scummvm executable to our Raspberry Pi (Raspbian OS) SD Card. A good idea is to create a scummvm folder in our /home/pi directory on the Raspian OS SD Card, and put the executable there along with any games we want to use with it.

In order to have the text-to-speech feature available for ScummVM we should also install the speech-dispatcher package and a text-to-speech engine (as per the instructions in this pertinent Pull Request)

For example we'd need to execute the following on our Raspbian OS on the Pi in order to use the espeak-ng text-to-speech engine:

sudo apt-get install --no-install-recommends speech-dispatcher speech-dispatcher-espeak-ng

Note 1: There's a number of optional additional files that can be copied in the ScummVM directory along with the scummvm executable, which ScummVM uses for themes, GUI translations and as auxilliary data files for some of the game engines. Such list of files is shown here.

Note 2: As of yet, there are some known issues with the ALSA sound driver especially in conjunction with the PulseAudio system on Raspbian OS (3.2). Having PulseAudio installed (by default it is not installed) may result to bad sound output in ScummVM (and other apps).

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