From 486b225bb34467c109dc9d69c0334736a461dcf1 Mon Sep 17 00:00:00 2001
From: zouhaitao <zhongxuanzhen@xtell.cn>
Date: Wed, 8 Jul 2026 13:21:32 +0800
Subject: [PATCH] feat: implement 4-bit SPI encoding at 3.0 MHz to align with
 byte boundaries and prevent gap stretching

---
 App/main.c | 48 ++++++++++++++----------------------------------
 1 file changed, 14 insertions(+), 34 deletions(-)

diff --git a/App/main.c b/App/main.c
index 39e5aa1..ce93606 100644
--- a/App/main.c
+++ b/App/main.c
@@ -128,29 +128,25 @@ void UI_ShowSosPage(void);
  * WS2812B 幻彩 LED 单线驱动函数 (24MHz 1T 模式下精准时序控制)
  * ========================================================================= */
 
-const u16 code SPI_LUT[16] = {
-    0x924, 0x926, 0x934, 0x936, 0x9A4, 0x9A6, 0x9B4, 0x9B6,
-    0xD24, 0xD26, 0xD34, 0xD36, 0xDA4, 0xDA6, 0xDB4, 0xDB6
-};
-
-void WS2812_EncodeByte(u8 v, u8 *buf)
+void WS2812_EncodeByte4(u8 v, u8 *buf)
 {
-    u16 p1 = SPI_LUT[v >> 4];
-    u16 p2 = SPI_LUT[v & 0x0F];
-    buf[0] = p1 >> 4;
-    buf[1] = ((p1 & 0x0F) << 4) | (p2 >> 8);
-    buf[2] = p2;
+    // Encode 8 FCOB bits into 4 SPI bytes (2 FCOB bits per byte)
+    // 0-code -> 1000 (binary), 1-code -> 1100 (binary)
+    buf[0] = ((v & 0x80) ? 0xC0 : 0x80) | ((v & 0x40) ? 0x0C : 0x08);
+    buf[1] = ((v & 0x20) ? 0xC0 : 0x80) | ((v & 0x10) ? 0x0C : 0x08);
+    buf[2] = ((v & 0x08) ? 0xC0 : 0x80) | ((v & 0x04) ? 0x0C : 0x08);
+    buf[3] = ((v & 0x02) ? 0xC0 : 0x80) | ((v & 0x01) ? 0x0C : 0x08);
 }
 
 void WS2812_Write24Bit(u8 g, u8 r, u8 b)
 {
-    u8 xdata buf[9];
+    u8 xdata buf[12];
     u8 i;
     u16 timeout;
     
-    WS2812_EncodeByte(g, &buf[0]);
-    WS2812_EncodeByte(r, &buf[3]);
-    WS2812_EncodeByte(b, &buf[6]);
+    WS2812_EncodeByte4(g, &buf[0]);
+    WS2812_EncodeByte4(r, &buf[4]);
+    WS2812_EncodeByte4(b, &buf[8]);
     
     EA = 0;
     
@@ -161,30 +157,14 @@ void WS2812_Write24Bit(u8 g, u8 r, u8 b)
     SPCTL = 0xD0; // Enable SPI at SYSCLK/4 (3.0 MHz actual clock on board)
     SPSTAT = 0xC0; // Clear flags
     
-    SPDAT = buf[0]; // Goes to shift register immediately
-    // Wait about 20 system cycles to avoid WCOL
-    _nop_(); _nop_(); _nop_(); _nop_(); _nop_(); 
-    _nop_(); _nop_(); _nop_(); _nop_(); _nop_(); 
-    _nop_(); _nop_(); _nop_(); _nop_(); _nop_(); 
-    _nop_(); _nop_(); _nop_(); _nop_(); _nop_(); 
-    SPDAT = buf[1]; // Goes to transmit buffer
-    
-    for (i = 2; i < 9; i++)
+    for (i = 0; i < 12; i++)
     {
+        SPDAT = buf[i];
         timeout = 2000;
-        while (!(SPSTAT & 0x80) && --timeout); // Wait with timeout
+        while (!(SPSTAT & 0x80) && --timeout); // Safe wait with timeout
         SPSTAT = 0xC0;
-        SPDAT = buf[i];          // Write buf[i] to transmit buffer (zero gap!)
     }
     
-    timeout = 2000;
-    while (!(SPSTAT & 0x80) && --timeout); // Wait for buf[7]
-    SPSTAT = 0xC0;
-    
-    timeout = 2000;
-    while (!(SPSTAT & 0x80) && --timeout); // Wait for buf[8]
-    SPSTAT = 0xC0;
-    
     SPCTL = 0x90; // Disable SPI
     WS2812_DI = 0;
     MOTOR = 0;   // Ensure motor is off