mirror of
https://github.com/sjlongland/atinysynth.git
synced 2025-11-03 05:51:08 +10:00
Stuart Longland
44e2d937d6
I left this out because I thought the idea of modulus and division on a
MCU that lacks a hardware multiplier would be too much for it… and
indeed it was too much with my other project.
Thinking about it this afternoon, I had an idea. If I have 2^N samples,
then the modulus can be optimised to:
```
mod = sample & ((2**n)-1)
```
and the segment can be figured out by:
```
segment = sample >> n
```
The segment is two bits. A function that returns the scaled sine value
for a given scaled angle can be given as:
```
int8_t fp_sine(uint8_t angle) {
uint8_t segment = (angle >> POLY_SINE_SZ_BITS) & 3;
uint8_t offset = angle & ((1 << POLY_SINE_SZ_BITS)-1);
switch (segment) {
case 0:
return _poly_sine[offset];
case 1:
return _poly_sine[
POLY_SINE_SZ - offset];
case 2:
return -_poly_sine[offset];
case 3:
return -_poly_sine[
POLY_SINE_SZ - offset];
}
}
```
… or something like that. If `POLY_SINE_SZ_BITS=6`, then `angle=255`
represents 360°.
53 lines
1.2 KiB
Makefile
53 lines
1.2 KiB
Makefile
# Compiler definitions
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CC = $(CROSS_COMPILE)gcc
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AR = $(CROSS_COMPILE)ar
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OBJCOPY = $(CROSS_COMPILE)objcopy
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OBJDUMP = $(CROSS_COMPILE)objdump
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SIZE = $(CROSS_COMPILE)size
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INCLUDES ?=
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LIBS ?=
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PORT ?= pc
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BINDIR ?= bin/$(PORT)
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PORTDIR ?= ports/$(PORT)
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OBJDIR ?= obj/$(PORT)
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SRCDIR ?= $(PWD)
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.PHONY: setfuse all clean
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-include local.mk
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include $(PORTDIR)/Makefile
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$(BINDIR)/synth: $(OBJDIR)/main.o $(OBJDIR)/poly.a
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@[ -d $(BINDIR) ] || mkdir -p $(BINDIR)
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$(CC) -g -o $@ $(LDFLAGS) $(LIBS) $^
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$(OBJDIR)/poly.a: $(OBJDIR)/adsr.o $(OBJDIR)/waveform.o
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$(AR) rcs $@ $^
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$(OBJDIR)/%.o: $(SRCDIR)/%.c
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@[ -d $(OBJDIR) ] || mkdir -p $(OBJDIR)
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$(CC) -o $@ -c $(CPPFLAGS) $(INCLUDES) $(CFLAGS) $<
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$(CC) -MM $(CPPFLAGS) $(INCLUDES) $< \
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| sed -e '/^[^ ]\+:/ s:^:$(OBJDIR)/:g' > $@.dep
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$(OBJDIR)/%.o: $(PORTDIR)/%.c
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@[ -d $(OBJDIR) ] || mkdir -p $(OBJDIR)
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$(CC) -o $@ -c $(CPPFLAGS) $(INCLUDES) $(CFLAGS) $<
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$(CC) -MM $(CPPFLAGS) $(INCLUDES) $< \
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| sed -e '/^[^ ]\+:/ s:^:$(OBJDIR)/:g' > $@.dep
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$(SRCDIR)/sine.c: $(SRCDIR)/gensine.py
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python $^ --amplitude 127 --num-samples-bits \
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--num-samples 6 --data-type int8_t \
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> $@
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clean:
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-rm -fr $(OBJDIR) $(BINDIR)
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$(BINDIR)/%.ihex: $(BINDIR)/%
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$(OBJCOPY) -j .text -j .data -O ihex $^ $@
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-include $(OBJDIR)/*.dep
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