After I finalised my case design, I shifted attention towards getting the Raspberry Pi configured to run games in the way I wanted. I basically wanted to be able to run existing python/pygame games on the device, making sure that the screen, audio and input from buttons via GPIO would all be working smoothly.
I started with the 27-05-2016 build of Raspbian, standard config for expanding the boot partition and configuring for a 104 key keyboard. I followed this guide for installing the kernel modules for the PiTFT 2.8 support. I wanted to use pygame and have support for the touchscreen, so I followed this guide to ensure the SDL version underneath pygame would support the screen (apparently needs to be SDL 1.2, there are reports of issues with SDL 2.0). I wrote a simple pygame app to test the touchscreen and test pre-installed gpio-connected buttons that came with the screen. I added a line at the top of the script before pygame.init() to ensure the SDL output was set to the framebuffer:
os.putenv('SDL_FBDEV', '/dev/fb1')
The touchscreen was working great, and very conveniently linked straight into the mouse drivers, such that touches come up as mouse click events in pygame. I added these lines in to get this happening:
os.putenv('SDL_MOUSEDRV', 'TSLIB')
os.putenv('SDL_MOUSEDEV', '/dev/input/touchscreen')
I used the python RPi.GPIO package, that came pre-insalled, to try and read button presses and at this point discovered the performance was fairly underwhelming: I was using event detection, and tried a combination of logic rules to read whether the pin was high or low, to detect short presses and long button holds, also tried playing with the bouncetime argument: all to no avail. I ended up realising that Adafruit had actually written a really nice c-based daemon, "Adafruit-Retrogame" which would map gpio events to key strokes: exactly what I wanted! And it worked perfectly: configured it to the keys I wanted, compiled it and added it to /etc/rc.local to run in the background on boot up.
Wireless: I setup my RPi to connect automatically to my wireless access point using this guide. I really wanted to get wireless working, as I knew from the case shell I wanted, it would be hard to feed one of the USB ports to the side for a keyboard or usb drive etc. (the other alternative for debugging would be a Bluetooth keyboard, but I still also wanted to be able to copy games on/off the device). I found the wireless would drop out constantly: turned off the pre-installed wireless power management: single line "sudo iwconfig wlan0 power off" added to /etc/rc.local to turn off every time on boot: wireless then working perfectly.
The last thing I did was to test the performance of one of my previous pyweek entries to see how it would go on the pi. The first thing I noticed was considerable audio lag for sounds (music was ok, but sounds would play at least 300-400 ms after being triggered) ... Found out I could fix this by reducing the buffer size using the following pre initialisation line in all python/pygame code:
pygame.mixer.pre_init(44100,-16,1,512)
More details on this here. The game was set to run at 30 fps, but I was only getting about 22-23 fps and the graphics were pretty choppy. I tweaked the PiTFT frame rate and SPI frequency by editing the settings in /boot/config.txt editing the relevant line to:
dtoverlay=pitft28r,rotate=90,speed=42000000,fps=30
After a bit of experimentation, these settings seemed the best balance for a not too choppy graphics and enough CPU left over to run the game smoothly.
Now that the Pi was setup, it was time to start putting all the hardware together!
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