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feat: prepend dummy byte 0x00 to SPI stream to absorb hardware startup glitch and keep first bit clean

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zouhaitao
2026-07-08 15:20:26 +08:00
parent d4513504d7
commit fdbb165dc7
1 changed files with 21 additions and 49 deletions
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70
App/main.c
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@@ -144,22 +144,17 @@ void WS2812_EncodeByte(u8 v, u8 *buf)
void WS2812_Write24Bit(u8 g, u8 r, u8 b)
{
u8 data buf[9];
u8 b0, b1, b2, b3, b4, b5, b6, b7, b8;
u8 data buf[10];
u8 b0, b1, b2, b3, b4, b5, b6, b7, b8, b9;
WS2812_EncodeByte(g, &buf[0]);
WS2812_EncodeByte(r, &buf[3]);
WS2812_EncodeByte(b, &buf[6]);
buf[0] = 0x00; // Prepend dummy 0x00 to absorb SPI hardware startup delay/glitch
WS2812_EncodeByte(g, &buf[1]);
WS2812_EncodeByte(r, &buf[4]);
WS2812_EncodeByte(b, &buf[7]);
b0 = buf[0];
b1 = buf[1];
b2 = buf[2];
b3 = buf[3];
b4 = buf[4];
b5 = buf[5];
b6 = buf[6];
b7 = buf[7];
b8 = buf[8];
b0 = buf[0]; b1 = buf[1]; b2 = buf[2]; b3 = buf[3];
b4 = buf[4]; b5 = buf[5]; b6 = buf[6]; b7 = buf[7];
b8 = buf[8]; b9 = buf[9];
EA = 0;
@@ -169,42 +164,19 @@ void WS2812_Write24Bit(u8 g, u8 r, u8 b)
SPSTAT = 0xC0; // Clear flags first
SPCTL = 0xD0; // Enable SPI at SYSCLK/4 (3.0 MHz actual clock on board)
SPDAT = b0; // Write immediately to avoid start glitch!
SPDAT = b0; // Send 0x00. MOSI remains low during startup delay!
while (!(SPSTAT & 0x80));
SPSTAT = 0xC0;
SPDAT = b1;
while (!(SPSTAT & 0x80));
SPSTAT = 0xC0;
SPDAT = b2;
while (!(SPSTAT & 0x80));
SPSTAT = 0xC0;
SPDAT = b3;
while (!(SPSTAT & 0x80));
SPSTAT = 0xC0;
SPDAT = b4;
while (!(SPSTAT & 0x80));
SPSTAT = 0xC0;
SPDAT = b5;
while (!(SPSTAT & 0x80));
SPSTAT = 0xC0;
SPDAT = b6;
while (!(SPSTAT & 0x80));
SPSTAT = 0xC0;
SPDAT = b7;
while (!(SPSTAT & 0x80));
SPSTAT = 0xC0;
SPDAT = b8;
while (!(SPSTAT & 0x80));
SPSTAT = 0xC0;
// Unrolled 10-byte transmission with minimal gap (~300ns)
while (!(SPSTAT & 0x80)); SPSTAT = 0xC0; SPDAT = b1;
while (!(SPSTAT & 0x80)); SPSTAT = 0xC0; SPDAT = b2;
while (!(SPSTAT & 0x80)); SPSTAT = 0xC0; SPDAT = b3;
while (!(SPSTAT & 0x80)); SPSTAT = 0xC0; SPDAT = b4;
while (!(SPSTAT & 0x80)); SPSTAT = 0xC0; SPDAT = b5;
while (!(SPSTAT & 0x80)); SPSTAT = 0xC0; SPDAT = b6;
while (!(SPSTAT & 0x80)); SPSTAT = 0xC0; SPDAT = b7;
while (!(SPSTAT & 0x80)); SPSTAT = 0xC0; SPDAT = b8;
while (!(SPSTAT & 0x80)); SPSTAT = 0xC0; SPDAT = b9;
while (!(SPSTAT & 0x80)); SPSTAT = 0xC0;
SPCTL = 0x90; // Disable SPI
WS2812_DI = 0;