In working through my Linux/Raspberry Pi eBook(Yes – the second eBook!), I’m up to the chapter where sounds are introduced using the SDL_mixer library. And I’ve hit two sets of problems.

It sometimes refuses to initialize the sound code.  This code below hits the LogError line:

	int success=Mix_OpenAudio(22050, AUDIO_S16LSB, 2, 8192);
	if (success==-1 ) {
		LogError("InitSetup failed to init audio");
	}

The other day it was working but not today. Now I have updated the Pi’s code (sudo apt update etc) but I wouldn’t have expected that to break it. I’ve been looking on the internet and find the whole thing a bit complicated.

I’ve got my Pi running 64-bit Raspberry Pi OS. I’ve changed the output device to headphones which plug into the headphone socket. If I run the VLC media player and tell it to play into the headphones, it will happily play the .wav files I’ve got for the asteroids game.

But if I run speaker-test, a terminal application with this command line

speaker-test -c2 -twav -l7 plughw:1,0

I get

speaker-test 1.2.4

Playback device is default
Stream parameters are 48000Hz, S16_LE, 2 channels
WAV file(s)
Setting of hwparams failed: Invalid argument

By running this command:

aplay -L

I got 71 lines of output but of these these below are the most important

output
hw:CARD=Headphones,DEV=0
    bcm2835 Headphones, bcm2835 Headphones

and the speaker-test command using the device parameter –Dhw:Headphones now worked. I’ve highlighted the bits in the aplay output needed to identify the device.

The new command  is

speaker-test -c2 -twav -l7 -Dhw:Headphones

I can now hear a female voice saying front left then front right a few times in my headphones.

So my Pi’s sound device is working; I just have to figure why SDL_mixer isn’t always. I’ll keep looking.

And the second problem which only occurs when the mixer is working, is when you play a lot of sounds. The PlayASound() function checks the result. On Windows it never had a problem but on Raspberry Pi, when you blow up a lot of asteroids say at one time, it plays a number of explosions then returns an error for each explosion after that. I think there’s only so many channels; that’s an easy fix; just ignore the error and return as if it succeeded.

So I’m reworking my original eBook for the Raspberry Pi, using software running on the Pi and developing a 2nd ebook. Along the way I’ll publish longer excerpts from it here. Probably one a week.

Silly me completely forgot that Raspberry Pis have a different CPU architecture compared to my PC. You just get used to something working on Linux and it was only after copying and it didn’t run that I realised my mistake. So I now have to recompile Asteroids (from Chapter-48.zip).

I’ve had a Raspberry-Pi 3 B+ for a year and wanted to run the Linux asteroids on it, now that I have it working on Ubuntu.

To do that I had to setup  Pi, running Raspbian downloaded from the Raspberry Pi website onto my Windows PC and then I used Win32 DiskImager (free Windows software) to burn the Raspbian OS onto a SD Card. Raspberry-Pis boot from SD Cards and the better and faster the SD card, the quicker the OS runs. Get a class 10 with A1 SD Card if you can.

After the Pi booted and Raspbian was installed and configured I had to enable SSH on the Pi; it’s disabled by default.

So now my PC was talking to the Pi using the excellent free WinSCP.  I copied all the files over, including the masks, sounds and images folders and all the source code and my exe built on Ubuntu which was the wrong file type. (Trying to run Intel code on an ARM- good luck with that!)

Now it turns out that the Raspbian version I installed (I’d gone for the Raspbian Buster with desktop and recommended software-2.5 GB download) included the non-dev version of SDL2. But as I needed to recompile the whole program, I had to install Visual Studio Code, Clang and the dev versions of SDL2, image and mixer.

Visual Studio Code on Arm?

Microsoft don’t do an official version for Raspberry-Pi or other ARM boards. However I discovered that a developer called Jay Rodgers has taken their source code (VS Code is open source) and  you can get a version from his site. It’s very usable on the Pi. Almost but not quite identical.

After installing the dev versions of libsdl2, image and mixer, I was almost able to compile it. I’d installed Clang but unlike the version on Ubuntu which was Clang-6, the version on Raspbian (based on Debian Buster) is Clang-7.

This means you have to edit the tasks.json file in the hidden .vscode folder. On line 25 where it says “command”: change the path to “/usr/bin/clang-7”.

That built ok, but when I ran it, it stopped with an error in the errorlog.txt file. For some reason, it failed loading the file “masks/am2.msk”.  Now I’d had no errors copying files from Windows to the Pi. This had been a very intermittent problem when copying several files in one go from Windows 10 to Ubuntu running under Hyper-V. Occasionally it would come up with some weird error but usually copied OK on the second go.

Despite several attempts, I could not get it to load that mask so as a temp fix I commented the line out. This means that one of the four asteroids sizes can never collide with anything. But it now ran.

However, I’m only getting about 25-27 fps with it in the early levels, not the 60 fps that I get on Ubuntu on other hardware. Given that the bulk of the work is blitting graphics, I suspect the GPU is just a bit under powered. Apparently on the Raspberry Pi 4, the GPU is newer and twice as fast as on the 3B+ so I’ll have to try it on a 4 when I get one. But the game works and is just about playable.

Now I’ll have to try and figure out why it won’t load that one mask. This has the makings of an interesting bug…