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https://github.com/tinygo-org/drivers.git
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Ayke van Laethem
7b56e61d52
Call a special __tinygo_ws2812_write_byte function to send a single byte.
82 lines
1.6 KiB
Go
82 lines
1.6 KiB
Go
// +build atsamd21
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package ws2812
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// This file implements the WS2812 protocol for 48MHz Cortex-M0
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// microcontrollers.
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import (
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"device/arm"
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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-M0 at 48MHz
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portSet, maskSet := d.Pin.PortMaskSet()
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portClear, maskClear := d.Pin.PortMaskClear()
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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: 10 cycles or 208.3ns
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// T0L: 39 cycles or 812.5ns -> together 49 cycles or 1020.8ns
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// T1H: 27 cycles or 562.5ns
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// T1L: 22 cycles or 458.3ns -> together 49 cycles or 1020.8ns
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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 @ [6]
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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 @ [15]
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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 @ [16]
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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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return nil
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}
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