mirror of
https://github.com/tinygo-org/drivers.git
synced 2026-08-16 04:43:25 +00:00
Daniel Bridges
177 lines
2.5 KiB
Go
177 lines
2.5 KiB
Go
// +build atsamd51 atsame5x
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package ws2812
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// This file implements the WS2812 protocol for 120MHz Cortex-M4
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// microcontrollers.
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// Note: This implementation does not work with tinygo 0.9.0 or older.
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import (
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"device/arm"
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"runtime/interrupt"
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)
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// Send a single byte using the WS2812 protocol.
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func (d Device) WriteByte(c byte) error {
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// For the Cortex-M4 at 120MHz
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portSet, maskSet := d.Pin.PortMaskSet()
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portClear, maskClear := d.Pin.PortMaskClear()
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mask := interrupt.Disable()
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// See:
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// https://wp.josh.com/2014/05/13/ws2812-neopixels-are-not-so-finicky-once-you-get-to-know-them/
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// T0H: 32-34 cycles or 266.67ns - 283.33ns
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// T0L: 101-103 cycles or 841.67ns - 858.33ns
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// +: 133-137 cycles or 1108.33ns - 1141.67ns
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// T1H: 73-75 cycles or 608.33ns - 625.00ns
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// T1L: 58-60 cycles or 483.33ns - 500.00ns
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// +: 131-135 cycles or 1091.67ns - 1125.00ns
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// A branch is treated here as 1-3 cycles, because apparently it might get
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// speculated. This is more of a guess than hard fact, because the only docs
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// by ARM that state this are now considered superseded (by what?).
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value := uint32(c) << 24
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arm.AsmFull(`
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1: @ send_bit
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str {maskSet}, {portSet} @ [2] T0H and T0L start here
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lsls {value}, #1 @ [1]
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nop @ [28]
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nop
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nop
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nop
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nop
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nop
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nop
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nop
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nop
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nop
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nop
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nop
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nop
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nop
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nop
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nop
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nop
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nop
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nop
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nop
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nop
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nop
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nop
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nop
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nop
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nop
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nop
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nop
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bcs.n 2f @ [1-3] skip_store
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str {maskClear}, {portClear} @ [2] T0H -> T0L transition
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2: @ skip_store
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nop @ [41]
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nop
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nop
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nop
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nop
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nop
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nop
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nop
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nop
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nop
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nop
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nop
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nop
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nop
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nop
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nop
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nop
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nop
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nop
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nop
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nop
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nop
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nop
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nop
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nop
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nop
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nop
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nop
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nop
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nop
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nop
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nop
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nop
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nop
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nop
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nop
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nop
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nop
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nop
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nop
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nop
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str {maskClear}, {portClear} @ [2] T1H -> T1L transition
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nop @ [54]
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nop
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nop
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nop
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nop
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nop
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nop
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nop
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nop
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nop
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nop
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nop
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nop
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nop
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nop
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nop
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nop
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nop
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nop
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nop
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nop
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nop
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nop
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nop
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nop
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nop
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nop
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nop
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nop
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nop
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nop
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nop
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nop
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nop
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nop
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nop
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nop
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nop
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nop
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nop
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nop
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nop
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nop
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nop
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nop
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nop
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nop
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nop
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nop
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nop
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nop
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nop
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nop
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nop
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subs {i}, #1 @ [1]
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bne.n 1b @ [1-3] send_bit
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`, map[string]interface{}{
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"value": value,
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"i": 8,
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"maskSet": maskSet,
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"portSet": portSet,
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"maskClear": maskClear,
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"portClear": portClear,
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})
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interrupt.Restore(mask)
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return nil
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}
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