From f2a20887b57ccad5286ee22d0fe6f8342df1750a Mon Sep 17 00:00:00 2001
From: Bad Diode <bd@badd10de.dev>
Date: Fri, 10 May 2024 22:32:21 +0200
Subject: Add a more accurate LSDJ sync method, including SO out

---
 src/sequencer.c | 116 +++++++++++++++++++++++---------------------------------
 src/settings.h  |   2 +
 2 files changed, 50 insertions(+), 68 deletions(-)

(limited to 'src')

diff --git a/src/sequencer.c b/src/sequencer.c
index 9e39cc7..4f57ec8 100644
--- a/src/sequencer.c
+++ b/src/sequencer.c
@@ -35,30 +35,6 @@ gate_set(u8 sc, u8 so) {
         | SIO_SI(0);
 }
 
-int pulses_sent = 0;
-int gate_status = 0;
-
-void
-gate_lsdj(void) {
-    gate_status ^= 1;
-    if (pulses_sent >= 7) {
-        gate_set(0, 0);
-        return;
-    }
-    if (gate_status == 1) {
-        gate_set(0, 0);
-    } else {
-        pulses_sent++;
-        gate_set(1, 0);
-    }
-    int n_ticks = -80 / 8 / 2; // 5ms
-    irs_set(IRQ_TIMER_3, gate_lsdj);
-    TIMER_DATA_3 = n_ticks;
-    TIMER_CTRL_3 = TIMER_CTRL_IRQ | TIMER_CTRL_ENABLE | TIMER_CTRL_FREQ_3;
-}
-
-// TODO: LSDJ sync pulse?
-
 //void
 //gate_on(void) {
 //    // SYNC24 NOTES
@@ -106,60 +82,56 @@ gate_lsdj(void) {
 //    // }
 //}
 
-bool first_pulse = true;
-int so_status = 1;
-
-void
-lsdj_toggle(void) {
-    gate_status ^= 1;
-    if (pulses_sent >= 7) {
-        TIMER_CTRL_3 = 0;
-        gate_set(1, so_status);
-        return;
-    }
-    if (gate_status == 1) {
-        gate_set(1, so_status);
-    } else {
-        pulses_sent++;
-        gate_set(0, so_status);
-    }
-    TIMER_CTRL_3 = 0;
-    // int n_ticks = -80 / 8 / 2; // 5ms
-    // irs_set(IRQ_TIMER_3, lsdj_toggle);
-    // TIMER_DATA_3 = n_ticks;
-    // TIMER_CTRL_3 = TIMER_CTRL_IRQ | TIMER_CTRL_ENABLE | TIMER_CTRL_FREQ_3;
-    int n_ticks = -9; // 122/2 = 61us; 61 / 3.8 = 16
-    irs_set(IRQ_TIMER_3, lsdj_toggle);
-    TIMER_DATA_3 = n_ticks;
-    TIMER_CTRL_3 = TIMER_CTRL_IRQ | TIMER_CTRL_ENABLE | TIMER_CTRL_FREQ_1;
-}
+int pulse_count = 0;
+int pulse_value = 0;
+int gate_status = 0;
 
 void
-lsdj_pulse(void) {
-    // LSDJ expects a pulse train on the SC pin (active low?). For the song
-    // start, the first pulse and until the start of the second one it should
-    // set SO to low as follows:
+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) --_______________________________-------------------------------
+    // OUT (SO) --__________----_________________-------------------------------
+    //
+    // Additionally, in LSDJ sync mode, at the start of each bar, SO should send
+    // the 0x01 byte (active low).
     //
-    // Additionally, in LSDJ sync mode, SO will go low at the start of each bar.
+    // 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).
-    if (first_pulse) {
-        first_pulse = false;
-        so_status = 0;
+    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 {
-        so_status = 1;
+        pulse_value = 0;
+        pulse_count = 0;
     }
+}
+
+void
+send_lsdj_pulse(u8 out_byte) {
+    pulse_value = out_byte;
+
+    // Reset timer.
     TIMER_DATA_3 = 0;
-    pulses_sent = 0;
+    pulse_value = out_byte;
+    pulse_count = 0;
     gate_status = 0;
-    gate_set(0, so_status);
     int n_ticks = -9; // 122/2 = 61us; 61 / 3.8 = 16
-    irs_set(IRQ_TIMER_3, lsdj_toggle);
+    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;
 }
@@ -607,10 +579,19 @@ sequencer_tick(void) {
     //     case SYNC_OUT_LINK_AUDIO_2BPQ: { if (sync_ticks++ % 48 == 0) { gate_on(); audio_sync_click = true; } } break;
     //     default: break;
     // }
+    // TODO: case sync_out_lsdj
+    if (sync_ticks++ % 4 == 0) {
+        u8 val = 0xff;
+        if ((sync_ticks - 1) == 0) {
+            val = 7; // DEBUG: Depends on pattern + bank.
+        } else if ((sync_ticks - 1) % 384 == 0) {
+            val = 253;
+        }
+        send_lsdj_pulse(val);
+    }
     if (nseq_ticks++ == 0) {
         play_step();
     }
-    if (sync_ticks++ % 4 == 0) { lsdj_pulse(); }
     if (nseq_ticks == 24) {
         nseq_ticks = 0;
     }
@@ -800,10 +781,9 @@ stop_sound(void) {
 
 void
 reset_sequencer(void) {
-    first_pulse = true;
-    so_status = 1;
+    TIMER_CTRL_3 = 0;
+    gate_set(1, 1);
     gate_status = 0;
-    pulses_sent = 0;
     step_counter = 0;
     nseq_ticks = 0;
     sync_ticks = 0;
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)",
-- 
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