6 files changed, 144 insertions, 32 deletions

diff --git a/Makefile b/Makefile
index e464b75..0e5cf83 100644
--- a/Makefile
+++ b/Makefile
@@ -27,7 +27,7 @@ INC_FLAGS   := $(addprefix -I,$(INC_DIRS))
 INC_FLAGS   += -I$(LIBGBA_SRC)
 
 # Output library names and executables.
-TARGET         := STEPPER-v1.8
+TARGET         := STEPPER-v1.9-dev-2
 ELF            := $(BUILD_DIR)/$(TARGET).elf
 BIN            := $(BUILD_DIR)/$(TARGET).gba
 
diff --git a/src/gba/gba.h b/src/gba/gba.h
index 3f629fd..1bb3afd 100644
--- a/src/gba/gba.h
+++ b/src/gba/gba.h
@@ -534,6 +534,14 @@ void irs_set(IrqIndex idx, IrsFunc func);
 // assembly and enable interrupts.
 void irq_init(void);
 
+// Only should be used inside an IrsFunc to enable it being interrupted by the
+// given interrupt (nested IRS).
+static inline void
+irs_interruptible(IrqIndex idx) {
+    IRQ_ENABLE |= (1 << idx);
+    IRQ_CTRL = 1;
+}
+
 //
 // BIOS function declarations.
 //
diff --git a/src/gba/interrupts.s b/src/gba/interrupts.s
index 67b9fe9..1d3e001 100644
--- a/src/gba/interrupts.s
+++ b/src/gba/interrupts.s
@@ -67,6 +67,10 @@ irs_main_handle_irs:
     bx      r2
     ldmfd   sp!, {lr}
 
+    @ Clear IRQ enable again just in case it was enabled from within the IRS.
+    mov r3, #0                      @ r3 = 0
+    strh r3, [ip, #8]               @ *(ip + 0x8) = r3
+
     @ Set CPU to irq mode
     mrs     r3, cpsr
     bic     r3, r3, #0xDF
diff --git a/src/sequencer.c b/src/sequencer.c
index 9efd506..64e0e49 100644
--- a/src/sequencer.c
+++ b/src/sequencer.c
@@ -22,35 +22,110 @@ clear_pattern(size_t idx) {
     redraw_bpm = true;
     redraw_params = true;
 }
-
-void
-gate_off(void) {
+INLINE void
+gate_set(u8 sc, u8 so) {
     SIO_MODE = SIO_MODE_GP
         | SIO_SC_OUT(1)
-        | SIO_SD_OUT(1)
-        | SIO_SI_OUT(0)
         | SIO_SO_OUT(1)
-        | SIO_SC(0)
+        | SIO_SD_OUT(0)
+        | SIO_SI_OUT(0)
+        | SIO_SC(sc)
+        | SIO_SO(so)
         | SIO_SD(0)
-        | SIO_SO(0);
+        | SIO_SI(0);
+}
+
+void
+gate_off(void) {
+     TIMER_CTRL_3 = 0;
+     gate_set(0, 0);
+}
+
+void
+gate_on(SyncSetting sync_mode) {
+     // SYNC24 NOTES
+     // (from https://e-rm.de/data/E-RM_report_HowToDinSync_10_14_EN.pdf)
+     //
+     // "Moreover, a duty cycle of 50% doesn't seem to be necessary, all tested
+     // machines were able to sync properly to clock ticks with a positive width
+     // of 5 ms to up to 300 BPM" @ 24bpq
+     //
+     // Since we want to use a 96bpq timer, we need to go 4 times faster (1.25ms
+     // per gate), though we could tailor the timing to the selected sync mode
+     // for less lenient machines.
+     gate_off();
+     gate_set(1, 1);
+     int n_ticks = 0;
+     switch (sync_mode) {
+         case SYNC_OUT_LINK_96BPQ: { n_ticks = -80 / 4; } break;
+         case SYNC_OUT_LINK_48BPQ: { n_ticks = -80 / 2; } break;
+         case SYNC_OUT_LINK_24BPQ: { n_ticks = -80; } break;
+         case SYNC_OUT_LINK_12BPQ: { n_ticks = -80 * 2; } break;
+         case SYNC_OUT_LINK_6BPQ:  { n_ticks = -80 * 4; } break;
+         case SYNC_OUT_LINK_4BPQ:  { n_ticks = -80 * 6; } break;
+         case SYNC_OUT_LINK_2BPQ:  { n_ticks = -80 * 12; } break;
+         default: break;
+     }
+     irs_set(IRQ_TIMER_3, gate_off);
+     TIMER_DATA_3 = n_ticks;
+     TIMER_CTRL_3 = TIMER_CTRL_IRQ | TIMER_CTRL_ENABLE | TIMER_CTRL_FREQ_3;
+}
+
+int pulse_count = 0;
+int pulse_value = 0;
+int gate_status = 0;
+
+void
+send_pulse(void) {
+    // LSDJ expects a pulse train on the SC pin (active low). For the song
+    // start, the first pulse indicates the starting row, for example, for row
+    // 0x06:
+    //
+    // CLK (SC) --_-_-_-_-_-_-_-_----------------_-_-_-_-_-_-_-_----------------
+    // OUT (SO) --__________----_________________-------------------------------
+    //
+    // Additionally, in LSDJ sync mode, at the start of each bar, SO should send
+    // the 0x01 byte (active low).
+    //
+    // CLK (SC) --_-_-_-_-_-_-_-_----------------_-_-_-_-_-_-_-_----------------
+    // OUT (SO) --____________--_________________-------------------------------
+    //
+    // The width of the pulse is approximately 915-916us (122us per pulse at 50%
+    // duty cycle of 61us). This sync method is based on sync24, so it should
+    // receive 6 pulses each 1/16th step (96 pulses in a 16 step sequence).
     TIMER_CTRL_3 = 0;
+    gate_set(gate_status, (pulse_value >> (7 - pulse_count)) & 0x1);
+    gate_status ^= 1;
+    if (gate_status == 0) {
+        pulse_count++;
+    }
+    if (pulse_count <= 7) {
+        int n_ticks = -9; // 122/2 = 61us; 61 / 3.8 = 16
+        irs_set(IRQ_TIMER_3, send_pulse);
+        TIMER_DATA_3 = n_ticks;
+        TIMER_CTRL_3 = TIMER_CTRL_IRQ | TIMER_CTRL_ENABLE | TIMER_CTRL_FREQ_1;
+    } else {
+        pulse_value = 0;
+        pulse_count = 0;
+    }
 }
 
 void
-gate_on(void) {
-    gate_off();
-    SIO_MODE = SIO_MODE_GP
-        | SIO_SC_OUT(1)
-        | SIO_SD_OUT(1)
-        | SIO_SI_OUT(0)
-        | SIO_SO_OUT(1)
-        | SIO_SC(1)
-        | SIO_SD(0)
-        | SIO_SO(1);
-    int n_ticks = -244181 / 600;
-    irs_set(IRQ_TIMER_3, gate_off);
+send_lsdj_pulse(u8 out_byte) {
+    // Reset timer.
+    TIMER_DATA_3 = 0;
+
+    // Set starting values.
+    gate_set(1, 1);
+    pulse_value = out_byte;
+    pulse_count = 0;
+    gate_status = 0;
+
+    // Start pulse message.
+    int n_ticks = -9; // 122/2 = 61us; 61 / 3.8 = 16
+    irs_set(IRQ_TIMER_3, send_pulse);
     TIMER_DATA_3 = n_ticks;
-    TIMER_CTRL_3 = TIMER_CTRL_IRQ | TIMER_CTRL_ENABLE | TIMER_CTRL_FREQ_3;
+    TIMER_CTRL_3 = TIMER_CTRL_IRQ | TIMER_CTRL_ENABLE | TIMER_CTRL_FREQ_1;
 }
 
 u8
@@ -475,22 +550,37 @@ env_start:
 
 void
 sequencer_tick(void) {
+    irs_interruptible(IRQ_VBLANK);  // Audio mix.
+    irs_interruptible(IRQ_TIMER_1); // Audio click sync.
+    irs_interruptible(IRQ_TIMER_3); // Link cable sync out.
+    irs_interruptible(IRQ_SERIAL); // Linc cable sync in.
     switch (settings.sync) {
-        case SYNC_OUT_LINK_96BPQ: { gate_on(); } break;
-        case SYNC_OUT_LINK_48BPQ: { if (sync_ticks++ % 2 == 0) { gate_on(); } } break;
-        case SYNC_OUT_LINK_24BPQ: { if (sync_ticks++ % 4 == 0) { gate_on(); } } break;
-        case SYNC_OUT_LINK_12BPQ: { if (sync_ticks++ % 8 == 0) { gate_on(); } } break;
-        case SYNC_OUT_LINK_6BPQ: { if (sync_ticks++ % 16 == 0) { gate_on(); } } break;
-        case SYNC_OUT_LINK_4BPQ: { if (sync_ticks++ % 24 == 0) { gate_on(); } } break;
-        case SYNC_OUT_LINK_2BPQ: { if (sync_ticks++ % 48 == 0) { gate_on(); } } break;
+        case SYNC_OUT_LINK_96BPQ: { gate_on(SYNC_OUT_LINK_96BPQ); } break;
+        case SYNC_OUT_LINK_48BPQ: { if (sync_ticks++ % 2 == 0) { gate_on(SYNC_OUT_LINK_48BPQ); } } break;
+        case SYNC_OUT_LINK_24BPQ: { if (sync_ticks++ % 4 == 0) { gate_on(SYNC_OUT_LINK_24BPQ); } } break;
+        case SYNC_OUT_LINK_12BPQ: { if (sync_ticks++ % 8 == 0) { gate_on(SYNC_OUT_LINK_12BPQ); } } break;
+        case SYNC_OUT_LINK_6BPQ: { if (sync_ticks++ % 16 == 0) { gate_on(SYNC_OUT_LINK_6BPQ); } } break;
+        case SYNC_OUT_LINK_4BPQ: { if (sync_ticks++ % 24 == 0) { gate_on(SYNC_OUT_LINK_4BPQ); } } break;
+        case SYNC_OUT_LINK_2BPQ: { if (sync_ticks++ % 48 == 0) { gate_on(SYNC_OUT_LINK_2BPQ); } } break;
         case SYNC_OUT_AUDIO_12BPQ: { if (sync_ticks++ % 8 == 0) { audio_sync_click = true; } } break;
         case SYNC_OUT_AUDIO_6BPQ: { if (sync_ticks++ % 16 == 0) { audio_sync_click = true; } } break;
         case SYNC_OUT_AUDIO_4BPQ: { if (sync_ticks++ % 24 == 0) { audio_sync_click = true; } } break;
         case SYNC_OUT_AUDIO_2BPQ: { if (sync_ticks++ % 48 == 0) { audio_sync_click = true; } } break;
-        case SYNC_OUT_LINK_AUDIO_12BPQ: { if (sync_ticks++ % 8 == 0) { gate_on(); audio_sync_click = true; } } break;
-        case SYNC_OUT_LINK_AUDIO_6BPQ: { if (sync_ticks++ % 16 == 0) { gate_on(); audio_sync_click = true; } } break;
-        case SYNC_OUT_LINK_AUDIO_4BPQ: { if (sync_ticks++ % 24 == 0) { gate_on(); audio_sync_click = true; } } break;
-        case SYNC_OUT_LINK_AUDIO_2BPQ: { if (sync_ticks++ % 48 == 0) { gate_on(); audio_sync_click = true; } } break;
+        case SYNC_OUT_LINK_AUDIO_12BPQ: { if (sync_ticks++ % 8 == 0) { gate_on(SYNC_OUT_LINK_12BPQ); audio_sync_click = true; } } break;
+        case SYNC_OUT_LINK_AUDIO_6BPQ: { if (sync_ticks++ % 16 == 0) { gate_on(SYNC_OUT_LINK_6BPQ); audio_sync_click = true; } } break;
+        case SYNC_OUT_LINK_AUDIO_4BPQ: { if (sync_ticks++ % 24 == 0) { gate_on(SYNC_OUT_LINK_4BPQ); audio_sync_click = true; } } break;
+        case SYNC_OUT_LINK_AUDIO_2BPQ: { if (sync_ticks++ % 48 == 0) { gate_on(SYNC_OUT_LINK_2BPQ); audio_sync_click = true; } } break;
+        case SYNC_OUT_LSDJ: {
+            if (sync_ticks++ % 4 == 0) {
+                u8 val = 0xff;
+                if ((sync_ticks - 1) == 0) {
+                    val = current_bank * 8 + current_pattern;
+                } else if ((sync_ticks - 1) % 384 == 0) {
+                    val = 253;
+                }
+                send_lsdj_pulse(val);
+            }
+        } break;
         default: break;
     }
     if (nseq_ticks++ == 0) {
@@ -684,6 +774,7 @@ stop_sound(void) {
 
 void
 reset_sequencer(void) {
+    TIMER_CTRL_3 = 0;
     step_counter = 0;
     nseq_ticks = 0;
     sync_ticks = 0;
@@ -1984,4 +2075,6 @@ sequencer_init(void) {
     SOUND_STATUS = SOUND_ENABLE;
     init_dsound();
     set_audio_settings();
+    // TODO: Set the gate to expected value depending on sync mode selected.
+    // Also applies to the reset_sequencer function.
 }
diff --git a/src/settings.c b/src/settings.c
index 8b4c3b1..e6f07f4 100644
--- a/src/settings.c
+++ b/src/settings.c
@@ -17,6 +17,7 @@ void sync_in_4(void);
 void reset_sequencer(void);
 void toggle_playing(void);
 void stop_playing(void);
+void gate_set(u8, u8);
 
 static int sync_ticks = 0;
 
@@ -65,6 +66,10 @@ set_audio_settings(void) {
                     | SOUND_DSOUND_RATIO_A
                     | SOUND_DSOUND_LEFT_A
                     | SOUND_DSOUND_RESET_A;
+            gate_set(0, 0);
+        } break;
+        case SYNC_OUT_LSDJ: {
+            gate_set(1, 1);
         } break;
         default: {
             SOUND_DMG_MASTER = sound_volume(SOUND_SQUARE1
diff --git a/src/settings.h b/src/settings.h
index bbfdfd2..73da88f 100644
--- a/src/settings.h
+++ b/src/settings.h
@@ -28,6 +28,7 @@ typedef enum SyncSetting {
     SYNC_OUT_LINK_AUDIO_6BPQ,
     SYNC_OUT_LINK_AUDIO_4BPQ,
     SYNC_OUT_LINK_AUDIO_2BPQ,
+    SYNC_OUT_LSDJ,
     SYNC_IN_LINK_96BPQ,
     SYNC_IN_LINK_48BPQ,
     SYNC_IN_LINK_24BPQ,
@@ -54,6 +55,7 @@ char * sync_setting_str[] = {
     "LINK+AUDIO OUT (6BPQ)",
     "LINK+AUDIO OUT (4BPQ)",
     "LINK+AUDIO OUT (2BPQ)",
+    "LSDJ OUT",
     "LINK IN (96BPQ)",
     "LINK IN (48BPQ)",
     "LINK IN (24BPQ)",