fix(c1): flush FPS pipeline + mute output to remove FPS on/off pop

FPS buffer (dsp_fps_out_buf) and algorithm delay-line state held stale samples across FPS-off periods, causing an occasional pop on re-enable. On CLOCKED_DOWN->ACTIVE, request fps1 to flush (zero buffers, reset positions, re-init library) before g_tile1_audio_ready=1, via a new FLUSHING state with req/ack handshake. Also arm a ~30ms proactive output mute in UserBufferManagement on every FPS toggle (g_fps_switch_mute) to mask the path-switch discontinuity in both directions. All C1_DFS_EN-guarded; factory unaffected.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

sw_usb_audio/app_usb_aud_fosi_c1/src/extensions/audiohw.xc

@@ -21,6 +21,9 @@
 #include "xua_hid_report.h"
 #include "nau88c21.h"
 #include "tile1_clk.h"
+#if C1_DFS_EN
+extern unsigned g_fps_switch_mute;   /* tile1_clk.xc: proactive mute on FPS toggle */
+#endif
 #include "dfu_upgrade.h"
 #if MQA_EN
 #include "MQA_XMOS.h"
@@ -219,6 +222,11 @@ void switch_mode_by_c1_mode(unsigned c1_mode, unsigned force_reboot)
     (void)force_reboot;
     {
         unsigned fps_val = (c1_mode == 4) ? 1u : 0u;
+        /* Mute the output around the path switch so neither the stale FPS
+         * buffer/algorithm tail (off->on) nor the FPS<->bypass discontinuity
+         * (on<->off) is audible. UserBufferManagement clears the mute after
+         * ~C1_SWITCH_MUTE_SAMPLES. */
+        SET_SHARED_GLOBAL(g_fps_switch_mute, 1);
         SET_SHARED_GLOBAL(g_3d_fps, fps_val);
         debug_printf("switch_mode_by_c1_mode: c1_mode=%d -> g_3d_fps=%d (no reboot)\n", c1_mode, fps_val);
     }

sw_usb_audio/app_usb_aud_fosi_c1/src/extensions/extra_i2s.xc

@@ -44,6 +44,7 @@ extern unsigned g_dnr_enable;
 extern unsigned g_adc_loop;
 #if C1_DFS_EN
 extern unsigned g_tile1_audio_ready;   /* tile1_clk.xc: state-machine output */
+extern unsigned g_fps_switch_mute;     /* tile1_clk.xc: proactive mute on FPS toggle */
 #endif
 #if UAC1
 #pragma unsafe arrays
@@ -74,6 +75,30 @@ void UserBufferManagement(unsigned sampsFromUsbToAudio[], unsigned sampsFromAudi
                 buffer_exchange((chanend)uc_br_data, sampsFromUsbToAudio, sampsFromAudioToUsb, 2);
         }
 
+#if C1_DFS_EN
+        /* Proactive output mute around FPS on/off: zeroes the playback path for
+         * ~C1_SWITCH_MUTE_SAMPLES after each toggle, masking the path-switch pop
+         * and the stale FPS data tail until the flushed pipeline refills. */
+        {
+            static unsigned sw_mute_samps = 0;
+            static unsigned prev_sw_mute = 0;
+            unsigned sw_mute;
+            GET_SHARED_GLOBAL(sw_mute, g_fps_switch_mute);
+            if (sw_mute)
+            {
+                if (!prev_sw_mute) sw_mute_samps = 0;   /* re-armed: restart count */
+                sampsFromUsbToAudio[0] = 0;
+                sampsFromUsbToAudio[1] = 0;
+                if (++sw_mute_samps >= C1_SWITCH_MUTE_SAMPLES)
+                {
+                    SET_SHARED_GLOBAL(g_fps_switch_mute, 0);
+                    sw_mute_samps = 0;
+                }
+            }
+            prev_sw_mute = sw_mute;
+        }
+#endif
+
         if (dnr_enable)
         {
             dnr_exchange_buffer((int32_t *)&sampsFromAudioToUsb[0]);

sw_usb_audio/app_usb_aud_fosi_c1/src/extensions/fps_wrapper.c

@@ -29,6 +29,10 @@ short __attribute__((aligned (4))) dsp_fps_out_buf[FPS_SLOT_NUM][FPS_PLANAR_SAMP
 unsigned fps_buf_ready = 0;
 unsigned fps_write_pos = 0;
 unsigned fps_process_pos = 0;
+/* Flush handshake (tile0 -> tile1): tile0 requests a flush before resuming audio
+ * after FPS re-enable; fps1 clears stale buffer + algorithm state, then acks. */
+unsigned g_fps_flush_req = 0;
+unsigned g_fps_flush_ack = 0;
 /* 改动原因：tile0/tile1 内存不共享；game/level/使能/fps_eq 须经 channel sync 写入 tile1 副本 */
 unsigned g_fps_game_select = 1;
 unsigned g_fps_level_select = 2;
@@ -239,12 +243,36 @@ static void fps_xmos_modules_init(void)
     fps_apply_module_enable();
 }
 
+/* Clear stale FPS pipeline state (zero the triple-buffer, reset positions, and
+ * re-initialise the algorithm library to flush its delay-line state). Called by
+ * fps1 on a flush request from tile0 so old samples/state are not played out. */
+static void fps_flush_pipeline(void)
+{
+    memset(dsp_fps_input_buf, 0, sizeof(dsp_fps_input_buf));
+    memset(dsp_fps_out_buf, 0, sizeof(dsp_fps_out_buf));
+    SET_SHARED_GLOBAL(fps_write_pos, 0);
+    SET_SHARED_GLOBAL(fps_process_pos, 0);
+    SET_SHARED_GLOBAL(fps_buf_ready, 0);
+    fps_xmos_modules_init();   /* reset algorithm library (delay lines etc.) */
+}
+
 void fps1_dsp_proc_task()
 {
     fps_xmos_modules_init();
 
     while (1)
     {
+        /* Service a flush request from tile0 (FPS re-enable): clear stale data
+         * before audio resumes, so old samples/state are not played out. */
+        unsigned flush_req;
+        GET_SHARED_GLOBAL(flush_req, g_fps_flush_req);
+        if (flush_req)
+        {
+            fps_flush_pipeline();
+            SET_SHARED_GLOBAL(g_fps_flush_req, 0);
+            SET_SHARED_GLOBAL(g_fps_flush_ack, 1);
+        }
+
         unsigned ready;
 
         GET_SHARED_GLOBAL(ready, fps_buf_ready);

sw_usb_audio/app_usb_aud_fosi_c1/src/extensions/tile1_clk.h

@@ -55,6 +55,12 @@
 #define C1_TILE1_ACTIVE            0
 #define C1_TILE1_PENDING_SHUTDOWN  1
 #define C1_TILE1_CLOCKED_DOWN      2
+#define C1_TILE1_FLUSHING          3  /* waiting for FPS pipeline flush before audio resume */
+
+/* Duration of the proactive output mute around an FPS on/off toggle, in audio
+ * samples (@ 48 kHz). Masks the path-switch discontinuity and covers the FPS
+ * pipeline flush + 1-frame refill. 2880 ~= 60 ms. */
+#define C1_SWITCH_MUTE_SAMPLES     2880
 
 /* One-time enable of the tile[1] core divider output path. MUST run on tile[1]. */
 void c1_tile1_clk_enable(void);

sw_usb_audio/app_usb_aud_fosi_c1/src/extensions/tile1_clk.xc

@@ -16,8 +16,11 @@
 unsigned g_audio_streaming   = 0;   /* 1 while USB audio is streaming */
 unsigned g_tile1_audio_ready = 0;   /* state-machine output: 1 => tile[0] may send to tile[1] */
 unsigned g_tile1_lp_div      = C1_TILE1_LP_XCORE_DIV_DEFAULT;
+unsigned g_fps_switch_mute   = 0;   /* set on FPS toggle: UserBufferManagement zeroes output for C1_SWITCH_MUTE_SAMPLES */
 
 extern unsigned g_3d_fps;           /* defined in extra_i2s.xc: 0=bypass, 1=FPS */
+extern unsigned g_fps_flush_req;    /* defined in fps_wrapper.c: flush FPS pipeline before audio resume */
+extern unsigned g_fps_flush_ack;    /* defined in fps_wrapper.c: ack flush complete */
 
 /* ---- state (tile[0]) ---- */
 static unsigned c1_tile1_state = C1_TILE1_ACTIVE;
@@ -152,8 +155,10 @@ void c1_tile1_power_tick(void)
                 c1_tile1_clock_up();                          /* restore-before-send */
                 unsigned t; c1_tile1_tmr :> t;
                 c1_tile1_tmr when timerafter(t + C1_TILE1_CLK_SETTLE_TICKS) :> void;
-                SET_SHARED_GLOBAL(g_tile1_audio_ready, 1);
+                /* Request FPS pipeline flush (clear stale buffer + algorithm)
-                c1_tile1_state = C1_TILE1_ACTIVE;
+                 * BEFORE audio resumes, so old samples are not played out. */
+                SET_SHARED_GLOBAL(g_fps_flush_req, 1);
+                c1_tile1_state = C1_TILE1_FLUSHING;
             }
             else
             {
@@ -161,6 +166,20 @@ void c1_tile1_power_tick(void)
                 c1_tile1_clock_down(g_tile1_lp_div);
             }
             break;
+
+        case C1_TILE1_FLUSHING:
+        {
+            /* Wait for fps1 to finish flushing the FPS pipeline, then resume audio. */
+            unsigned ack;
+            GET_SHARED_GLOBAL(ack, g_fps_flush_ack);
+            if (ack)
+            {
+                SET_SHARED_GLOBAL(g_fps_flush_ack, 0);
+                SET_SHARED_GLOBAL(g_tile1_audio_ready, 1);
+                c1_tile1_state = C1_TILE1_ACTIVE;
+            }
+        }
+        break;
     }
 }