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improve SAMx5x NeoPixel timings #6280

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improve SAMx5x NeoPixel timings #6280

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640dede
improve SAMx5x NeoPixel timings
dhalbert Apr 13, 2022
02f6726
further NeoPixel tuning, but needs testing
dhalbert Apr 14, 2022
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31 changes: 27 additions & 4 deletions ports/atmel-samd/common-hal/neopixel_write/__init__.c
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Original file line number Diff line number Diff line change
Expand Up @@ -46,6 +46,29 @@ __attribute__((naked,noinline,aligned(16)))
static void neopixel_send_buffer_core(volatile uint32_t *clraddr, uint32_t pinMask,
const uint8_t *ptr, int numBytes);

// From the SK6812 datasheet:
// T0H 0 code, high level time 0.3µs ±0.15µs
// T1H 1 code, high level time 0.6µs ±0.15µs
// T0L 0 code, low level time 0.9µs ±0.15µs
// T1L 1 code, low level time 0.6µs ±0.15µs
// Trst Reset code，low level time 80µs

// From the WS2812 datasheet:
// T0H 0 code, high voltage time 0.35us ±150ns
// T1H 1 code, high voltage time 0.7us ±150ns
// T0L 0 code, low voltage time 0.8us ±150ns
// T1L 1 code, low voltage time 0.6us ±150ns
// RES low voltage time Above 50µs

// From the WS28212B datasheet:
// T0H 0 code, high voltage time 0.4us ±150ns
// T1H 1 code, high voltage time 0.8us ±150ns
// T0L 0 code, low voltage time 0.85us ±150ns
// T1L 1 code, low voltage time 0.45us ±150ns
// RES low voltage time Above 50µs

// The SAMDx5x timings do not correspond to the SAMD21 timings. The SAMDx5x were determined
// by looking at the output of an SK6812, and trying to match what it sent.
static void neopixel_send_buffer_core(volatile uint32_t *clraddr, uint32_t pinMask,
const uint8_t *ptr, int numBytes) {
asm volatile (" push {r4, r5, r6, lr};"
Expand All @@ -60,7 +83,7 @@ static void neopixel_send_buffer_core(volatile uint32_t *clraddr, uint32_t pinMa
" movs r6, #3; d2: sub r6, #1; bne d2;" // delay 3
#endif
#ifdef SAM_D5X_E5X
" movs r6, #16; d2: subs r6, #1; bne d2;" // delay 3
" movs r6, #11; d2: subs r6, #1; bne d2;" // 302 ns high (entire T0H or start T1H)
#endif
" tst r4, r5;" // mask&r5
" bne skipclr;"
Expand All @@ -70,7 +93,7 @@ static void neopixel_send_buffer_core(volatile uint32_t *clraddr, uint32_t pinMa
" movs r6, #6; d0: sub r6, #1; bne d0;" // delay 6
#endif
#ifdef SAM_D5X_E5X
" movs r6, #16; d0: subs r6, #1; bne d0;" // delay 6
" movs r6, #11; d0: subs r6, #1; bne d0;" // 302 ns low or high (start T0L or end T1H)
#endif
" str r1, [r0, #0];" // clr (possibly again, doesn't matter)
#ifdef SAMD21
Expand All @@ -85,12 +108,12 @@ static void neopixel_send_buffer_core(volatile uint32_t *clraddr, uint32_t pinMa
" movs r6, #2; d1: sub r6, #1; bne d1;" // delay 2
#endif
#ifdef SAM_D5X_E5X
" movs r6, #15; d1: subs r6, #1; bne d1;" // delay 2
" movs r6, #22; d1: subs r6, #1; bne d1;" // 606 ns (end TOL or entire T1L)
#endif
" b loopBit;"
"nextbyte:"
#ifdef SAM_D5X_E5X
" movs r6, #12; d3: subs r6, #1; bne d3;" // delay 2
" movs r6, #6; d3: subs r6, #1; bne d3;" // byte delay FIGURE THIS OUT
#endif
" cmp r2, r3;"
" bcs neopixel_stop;"
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