m68k: add new "interrupt" example

I don't completely understand how the scsp timers work; "8192" is a
magic number I came up with by experimentation.

Makefile

@@ -84,7 +84,9 @@ m68k:
 m68k/%.bin: m68k
 	$(MAKE) -C m68k $(notdir $@)
 
-scsp/sound_cpu.elf: scsp/sound_cpu.o m68k/slot.bin.o
+scsp/sound_cpu__slot.elf: scsp/sound_cpu__slot.o m68k/slot.bin.o
+
+scsp/sound_cpu__interrupt.elf: scsp/sound_cpu__interrupt.o m68k/interrupt.bin.o
 
 # clean
 clean: clean-sh

m68k/Makefile

@@ -9,4 +9,6 @@ include $(LIB)/m68k/common.mk
 %.pcm.o: %.pcm
 	$(BUILD_BINARY_O)
 
-slot.elf: $(LIB)/m68k/vectors.o slot.o sine-44100-s16be-1ch.pcm.o
+slot.elf: $(LIB)/m68k/vectors.o $(LIB)/m68k/handlers.o slot.o sine-44100-s16be-1ch.pcm.o
+
+interrupt.elf: $(LIB)/m68k/vectors.o $(LIB)/m68k/handlers.o interrupt.o jojo-11025-s16be-1ch.pcm.o

m68k/interrupt.cpp

@@ -0,0 +1,88 @@
+#include <stdint.h>
+
+#include "scsp.h"
+
+extern void * _jojo_start __asm("_binary_jojo_11025_s16be_1ch_pcm_start");
+
+static volatile int32_t frame = 0;
+
+extern "C"
+void auto_vector_1(void) __attribute__ ((interrupt_handler));
+void auto_vector_1(void)
+{
+  // reset TIMER_A interrupt
+  scsp.reg.ctrl.SCIRE = INT__TIMER_A;
+
+  frame++;
+  //if (frame > 3962) frame = 0;
+  
+  const uint16_t * jojo_start = reinterpret_cast<uint16_t *>(&_jojo_start);
+  const uint32_t frame_addr = reinterpret_cast<uint32_t>(&jojo_start[frame * 8192]);
+  
+  scsp_slot& slot = scsp.reg.slot[frame % 32];
+  slot.LOOP = 0;
+  slot.LOOP |= LOOP__KYONEX;
+  
+  slot.LOOP = LOOP__KYONB | LOOP__SA(frame_addr); // kx kb sbctl[1:0] ssctl[1:0] lpctl[1:0] 8b sa[19:16]
+  slot.SA = SA__SA(frame_addr); // start address (bytes)
+  slot.LSA = 0; // loop start address (samples)
+  slot.LEA = 8192; // loop end address (samples)
+  slot.EG = EG__AR(0x1f) | EG__EGHOLD; // d2r d1r ho ar krs dl rr
+  slot.VOLUME = 0; // stwinh sdir tl
+  slot.FM = 0; // mdl mdxsl mdysl
+  slot.PITCH = PITCH__OCT(-2) | PITCH__FNS(0); // oct fns
+  slot.LFO = 0; // lfof plfows
+  slot.MIXER = MIXER__DISDL(0b101); // disdl dipan efsdl efpan
+
+  slot.LOOP |= LOOP__KYONEX;
+  
+  return;
+}
+
+void main()
+{
+  for (long i = 0; i < 807; i++) { asm volatile ("nop"); }   // wait for (way) more than 30µs
+  
+  scsp.reg.ctrl.MIXER = MIXER__MEM4MB | MIXER__MVOL(0xf);
+
+  scsp.reg.ctrl.TIMA = TIMA__TACTL(7);
+
+  // timer A is vector 1 (0b001)
+  scsp.reg.ctrl.SCILV2 = 0;
+  scsp.reg.ctrl.SCILV1 = 0;
+  scsp.reg.ctrl.SCILV0 = SCILV__TIMER_A;
+  
+  // enable TIMER_A
+  scsp.reg.ctrl.SCIRE = INT__TIMER_A;
+  scsp.reg.ctrl.SCIEB = INT__TIMER_A;
+  
+  asm volatile ("move.w #8192,%sr");
+
+  const uint16_t * jojo_start = reinterpret_cast<uint16_t *>(&_jojo_start);
+  const uint32_t frame_addr = reinterpret_cast<uint32_t>(&jojo_start[frame * 128]);
+  
+  scsp_slot& slot = scsp.reg.slot[0];
+  slot.LOOP = 0;
+  slot.LOOP |= LOOP__KYONEX;
+  
+  slot.LOOP = LOOP__KYONB | LOOP__SA(frame_addr); // kx kb sbctl[1:0] ssctl[1:0] lpctl[1:0] 8b sa[19:16]
+  slot.SA = SA__SA(frame_addr); // start address (bytes)
+  slot.LSA = 0; // loop start address (samples)
+  slot.LEA = 128; // loop end address (samples)
+  slot.EG = EG__AR(0x1f) | EG__EGHOLD; // d2r d1r ho ar krs dl rr
+  slot.VOLUME = 0; // stwinh sdir tl
+  slot.FM = 0; // mdl mdxsl mdysl
+  slot.PITCH = PITCH__OCT(-2) | PITCH__FNS(0); // oct fns
+  slot.LFO = 0; // lfof plfows
+  slot.MIXER = MIXER__DISDL(0b101); // disdl dipan efsdl efpan
+
+  slot.LOOP |= LOOP__KYONEX;  
+}
+
+extern "C"
+void start(void)
+{
+  main();
+  while (1);
+}
+

m68k/slot.cpp

@@ -1,8 +1,6 @@
 #include <stdint.h>
-#include "smpc.h"
-#include "scsp.h"
 
-#include "../common/copy.hpp"
+#include "scsp.h"
 
 extern void * _sine_start __asm("_binary_sine_44100_s16be_1ch_pcm_start");
 
@@ -15,6 +13,9 @@ void main()
   const uint32_t sine_start = reinterpret_cast<uint32_t>(&_sine_start);
 
   scsp_slot& slot = scsp.reg.slot[0];
+  slot.LOOP = 0;
+  slot.LOOP |= LOOP__KYONEX;
+  
   slot.LOOP = LOOP__KYONB | LOOP__LPCTL__NORMAL | LOOP__SA(sine_start); // kx kb sbctl[1:0] ssctl[1:0] lpctl[1:0] 8b sa[19:16]
   slot.SA = SA__SA(sine_start); // start address (bytes)
   slot.LSA = 0; // loop start address (samples)

scsp/sound_cpu__interrupt.cpp

@@ -5,8 +5,8 @@
 
 #include "../common/copy.hpp"
 
-extern void * _binary_m68k_slot_bin_start __asm("_binary_m68k_slot_bin_start");
+extern void * _m68k_start __asm("_binary_m68k_interrupt_bin_start");
-extern void * _binary_m68k_slot_bin_size __asm("_binary_m68k_slot_bin_size");
+extern void * _m68k_size __asm("_binary_m68k_interrupt_bin_size");
 
 void main()
 {
@@ -23,8 +23,8 @@ void main()
 
   scsp.reg.ctrl.MIXER = MIXER__MEM4MB;
   
-  uint32_t * m68k_main_start = (uint32_t *)&_binary_m68k_slot_bin_start;
+  uint32_t * m68k_main_start = reinterpret_cast<uint32_t*>(&_m68k_start);
-  uint32_t m68k_main_size = (uint32_t)&_binary_m68k_slot_bin_size;
+  uint32_t m68k_main_size = reinterpret_cast<uint32_t>(&_m68k_size);
   copy<uint32_t>(&scsp.ram.u32[0], m68k_main_start, m68k_main_size);
   
   while ((smpc.reg.SF & 1) != 0);

scsp/sound_cpu__slot.cpp

@@ -0,0 +1,43 @@
+#include <stdint.h>
+
+#include "smpc.h"
+#include "scsp.h"
+
+#include "../common/copy.hpp"
+
+extern void * _m68k_start __asm("_binary_m68k_slot_bin_start");
+extern void * _m68k_size __asm("_binary_m68k_slot_bin_size");
+
+void main()
+{
+  /* SEGA SATURN TECHNICAL BULLETIN # 51
+
+     The document suggests that Sound RAM is (somewhat) preserved
+     during SNDOFF.
+   */
+  
+  while ((smpc.reg.SF & 1) != 0);
+  smpc.reg.SF = 1;
+  smpc.reg.COMREG = COMREG__SNDOFF;
+  while (smpc.reg.oreg[31] != OREG31__SNDOFF);
+
+  scsp.reg.ctrl.MIXER = MIXER__MEM4MB;
+  
+  uint32_t * m68k_main_start = reinterpret_cast<uint32_t*>(&_m68k_start);
+  uint32_t m68k_main_size = reinterpret_cast<uint32_t>(&_m68k_size);
+  copy<uint32_t>(&scsp.ram.u32[0], m68k_main_start, m68k_main_size);
+  
+  while ((smpc.reg.SF & 1) != 0);
+  smpc.reg.SF = 1;
+  smpc.reg.COMREG = COMREG__SNDON;
+  while (smpc.reg.oreg[31] != OREG31__SNDON);
+  
+  // do nothing while the sound CPU manipulates the SCSP
+}
+
+extern "C"
+void start(void)
+{
+  main();
+  while (1);
+}