Add dsp

With:
- LED control
- UART
- PDM out
- square wave generator (DMA to PDM out (was it really necessary?))
- sample program that plays a square wave from UART values

dsp/makefile

@@ -0,0 +1,39 @@
+all: sim rom
+sim: dsp_test.ghw
+rom: boot_rom.gen.vhdl
+
+CC = ../bin/cc
+LD = ../bin/ld
+
+CFLAGS = -I../wave -I../uart
+
+boot_rom.gen.vhdl: main.o ../uart/uart.o
+
+sim_sources = dsp_test.vhdl
+sources = boot_rom.gen.vhdl dsp.vhdl      \
+	  ../cpu/cpu.vhdl ../cpu/reg.vhdl \
+	  $(wildcard ../wave/*.vhdl)      \
+	  $(wildcard ../sysbus/*.vhdl)    \
+	  ../uart/uart.vhdl               \
+	  ../first/ram.vhdl
+
+
+%.gen.vhdl:
+	$(LD) -o $@ --vhdl $*.vhdl.in $^
+
+
+%.ghw: work-obj93.cf
+	ghdl -r $* --wave=$@ --assert-level=error
+
+
+work-obj93.cf: $(sim_sources) $(sources)
+	ghdl -a $^
+
+PHONY: sim clean
+
+clean:
+	rm -rf *.o *.gen.vhdl *.ghw work-obj93.cf
+
+.DELETE_ON_ERROR:
+
+.PRECIOUS: %.ghw