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Ron Evans
51 lines
1.6 KiB
Go
51 lines
1.6 KiB
Go
// +build digispark
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package ws2812
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// This file implements the WS2812 protocol for 16.5MHz Digispark AVR microcontrollers.
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// This is a slightly different implementation than the one for the atmega to work around a compiler bug.
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import (
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"device/avr"
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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 AVR at 16MHz
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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: 4 cycles or 250ns
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// T0L: 14 cycles or 875ns -> together 18 cycles or 1125ns
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// T1H: 9 cycles or 562ns
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// T1L: 8 cycles or 500ns -> together 17 cycles or 1062ns
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avr.AsmFull(`
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send_bit:
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st {portSet}, {maskSet} ; [2] set output high
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lsl {value} ; [1] shift off the next bit, store it in C
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brcs skip_store ; [1/2] branch if this bit is high (long pulse)
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st {portClear}, {maskClear} ; [2] set output low (short pulse)
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skip_store:
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nop ; [4] wait before changing the output again
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nop
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nop
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nop
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st {portClear}, {maskClear} ; [2] set output low (end of pulse)
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nop ; [3]
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nop
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nop
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subi {i}, 1 ; [1] subtract one (for the loop)
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brne send_bit ; [1/2] send the next bit, if not at the end of the loop
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`, map[string]interface{}{
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"value": c,
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"i": byte(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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