mirror of
https://github.com/tinygo-org/drivers.git
synced 2026-08-14 11:53:41 +00:00
Ayke van Laethem
00a9b9db77
This has cost me _hours_ to find. There are many clones of the ws2812 and they have slightly different timing characteristics. Some don't work so well when you get close to the minimum T1H time: a 1-bit may be interpreted as a 0-bit.
111 lines
2.0 KiB
Go
111 lines
2.0 KiB
Go
// +build nrf52
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package ws2812
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// This file implements the WS2812 protocol for 64MHz Cortex-M4
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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-M4 at 64MHz
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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: 17-19 cycles or 265.63ns - 296.88ns
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// T0L: 54-56 cycles or 843.75ns - 875.00ns
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// +: 71-75 cycles or 1109.38ns - 1171.88ns
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// T1H: 39-41 cycles or 609.38ns - 640.63ns
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// T1L: 30-32 cycles or 468.75ns - 500.0ns
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// +: 69-73 cycles or 1078.13ns - 1140.63ns
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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// by ARM that state this are now considered superseded (by what?).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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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 @ [10]
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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 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 @ [22]
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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 @ [26]
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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 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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