apu: Add sound support about peanut-gb

[deltabeard]

WIP on apu branch. Currently passes dmg_sound/01-registers.gb test.
Next is length counters.

[deltabeard]

A test build with blarrgs audio library is working. It did crash on a failed assertion though (lost three hours of gameplay because of it). It uses C++, so compiling everything and linking it all together was a pain. Not interested in using it.

[deltabeard]

SDL2 example now uses blarrgs audio library for sound since commit 0ba5996.
As a workaround to the many asserts in blarrgs audio library, the SDL2 example now records the save file every minute.

I do not want to continue using blarrgs audio library due to the following issues:

• It's not a single file header library like peanut_gb.h
• It doesn't recover from certain issues, instead it uses asserts which abort the emulator.
• It uses separate timing to the emulator. If this timing is only marginally off, then the sound will not be good. A feature like automatic sample rate change would be nice.
• It's written in C++, and I only know C fluently.

So I'll keep this issue open.

[deltabeard]

Got a segfault caused by blarrgs APU:

#0  0x0000557402a98ff7 in Blip_Synth<3, 210>::offset_resampled(unsigned long, int, Blip_Buffer*) const ()
#1  0x0000557402a98ed6 in Gb_Square::run(long, long) ()
#2  0x0000557402a98407 in Gb_Apu::run_until(long) ()
#3  0x0000557402a984b0 in Gb_Apu::end_frame(long) ()
#4  0x0000557402a975df in Basic_Gb_Apu::end_frame() ()
#5  0x0000557402a97123 in main (argc=2, argv=<optimized out>) at peanut_sdl.c:665

[deltabeard]

Look at whether peanut_apu resolves this issue, or at least describe any changes required.

[deltabeard]

Work being done on a 16-bit APU at https://github.com/deltabeard/Peanut-GB/tree/apu_s16

[deltabeard]

Branch merged. f501adc

[deltabeard]

The APU will remain separate to Peanut-GB. The 16-bit APU can be found in https://github.com/deltabeard/Peanut-GB/tree/master/examples/sdl2/minigb_apu .