gameboy_inspiration.md

Inspiration

register-like behaviour of waveform generators

e.g. in gameboy:

	       Square 1
	NR10 FF10 -PPP NSSS Sweep period, negate, shift
	NR11 FF11 DDLL LLLL Duty, Length load (64-L)
	NR12 FF12 VVVV APPP Starting volume, Envelope add mode, period
	NR13 FF13 FFFF FFFF Frequency LSB
	NR14 FF14 TL-- -FFF Trigger, Length enable, Frequency MSB

A timer generates an output clock every N input clocks --> gb frequency = 4194304 (4.19MHz) a timer's rate is given as a frequency, its period is 4194304/frequency in Hz

Ts = (2048-frequency)*4 //square wave period. T1 = N/4194304 //Timer1 period. Tfreq =

Square waves use this clock as input. Translating to PWM in avr

###Sequencer Steps at 512Hz

Step   Length Ctr  Vol Env     Sweep
---------------------------------------
0      Clock       -           -
1      -           -           -
2      Clock       -           Clock
3      -           -           -
4      Clock       -           -
5      -           -           -
6      Clock       -           Clock
7      -           Clock       -
---------------------------------------
Rate   256 Hz      64 Hz       128 Hz

###Code //Runs at 512 Hz volatile byte GBT1Counter; //Tie ocr0b frequency to gameboy frequency //Period F_CPU SequencerISR{ counterLength++; counterVolumeEnvelope++; counterSweep

clockLength();
clockVolume();
clockSweep();

}

GBSPlay

Use gbsplay -o iodumper to check the cycles-diff and the instruction to which registers. Modified iodumper to output raw bytes. Progmem read

./gbsplay -o iodumper song.gbs  > song.hex
#limit xxd output to n bytes
xxd -i -len 16000 song.hex song.h 

Instruction written in byte format;

typedef struct {
            long    elapsed;
            uint8_t addr;
            uint8_t val;
} gbs_instr;