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Ayke van Laethem
d80f619c9f
The timings needed to be changed slightly for ws2811 chips which are slightly slower.
53 lines
1.4 KiB
Go
53 lines
1.4 KiB
Go
// +build nrf51
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package ws2812
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// This file implements the WS2812 protocol for 16MHz 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 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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// Note: timings have been increased slightly to also support ws2811 LEDs.
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// T0H: 5 cycles or 312.5ns
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// T0L: 14 cycles or 875.0ns -> together 19 cycles or 1187.5ns
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// T1H: 11 cycles or 687.5ns
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// T1H: 8 cycles or 500.0ns -> together 19 cycles or 1187.5ns
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value := uint32(c) << 24
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arm.AsmFull(`
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send_bit:
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str {maskSet}, {portSet} @ [2] T0H and T0L start here
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nop @ [1]
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lsls {value}, #1 @ [1]
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bcs.n skip_store @ [1/3]
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str {maskClear}, {portClear} @ [2] T0H -> T0L transition
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skip_store:
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nop @ [4]
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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 @ [2]
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nop
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subs {i}, #1 @ [1]
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bne.n send_bit @ [1/3]
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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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