zephyr/drivers/led_strip/Kconfig.ws2812
Marti Bolivar bdde886ed5 led_strip: ws2812: HACK: memory-hungry pulse timing bugfix
At least on nRF52 devices, we are taking too much time between pixels
dealing with overhead inside the SPI driver transceive calls. This is
leading to dropped frames, because the dead time between frames is
long enough (5000ns+) to look like a reset pulse to the LED strip.

Given this SPI driver limitation, it seems this LED driver's design
decision to rely on SPI peripherals as efficient pulse generators
doesn't work well in practice.

The right way to handle this is probably to switch from SPI to
efficient inline assembly which bit-bangs the pulses with interrupts
disabled.

This is what other efficient libraries do to drive this type of
LED (e.g. FastLED uses C++ templates that expand into such
assembly). The Zephyr GPIO API doesn't support doing that in a
portable fashion, unfortunately.

For now, we'll cheat by pre-allocating enough buffer space to send the
entire strip's worth of data.

This is preposterously inefficient (8x memory overhead since there's
one byte to make a SPI frame for each bit of color), but makes the
driver work correctly.

(Note that using timer peripherals as pulse generators, when combined
with DMA for efficiency, would also lead to similar levels of
overhead.)

Signed-off-by: Marti Bolivar <marti@opensourcefoundries.com>
2018-10-15 17:50:16 +02:00

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#
# Copyright (c) 2017 Linaro Limited
#
# SPDX-License-Identifier: Apache-2.0
#
# The following blog post is an excellent resource about pulse timing:
#
# https://wp.josh.com/2014/05/13/ws2812-neopixels-are-not-so-finicky-once-you-get-to-know-them/
menuconfig WS2812_STRIP
bool "Enable WS2812 (and compatible) LED strip driver"
depends on SPI
help
Enable LED strip driver for daisy chains of WS2812-ish
(or WS2812B, WS2813, SK6812, or compatible) devices.
These devices have a one-wire communications interface
which encodes bits using pulses. Short pulses indicate
zero bits, and long pulses indicate ones; refer to the
chip datasheets for precise specifications. To implement
this in a multitasking operating system, this driver
generates the pulses using a SPI peripheral.
if WS2812_STRIP
config WS2812_STRIP_NAME
string "Driver name"
default "ws2812_strip"
help
Device name for WS2812 LED strip.
config WS2812_STRIP_MAX_PIXELS
int "Maximum number of pixels in a strip"
default 12
help
Set this to the maximum number of pixels you need
to control at once. There is an 8x memory penalty associated
with each increment of this value, so it's worth optimizing.
config WS2812_STRIP_SPI_DEV_NAME
string "SPI master to use to drive the strip"
default ""
help
Specify the device name of the SPI master which the
WS2812 driver should use to control the LED strip.
The MOSI pin of this SPI peripheral should be connected
to the signal pin for the first chip in the strip.
Examples: SPI_0, SPI_1, etc.
config WS2812_STRIP_SPI_BAUD_RATE
int "Baud rate to use to drive LED strip"
default 5250000
help
SPI clock rate, in Hz, to use while driving the strip.
The baud rate must be chosen carefully together with the
WS2812_STRIP_SPI_ONE_FRAME and WS2812_STRIP_SPI_ZERO_FRAME
values so that the transmitted frames meet the chipset
pulse widths for one and zero bits. If unsure, keep the default,
but enable SPI debug logging for your device and make sure the
configuration is matched exactly at runtime.
config WS2812_STRIP_ONE_FRAME
hex "SPI frame to shift out to signal a one bit"
default 0x7c
help
When shifted out at the configured clock frequency,
this must generate a pulse whose width fits within the chipset
specifications for T1H, and whose interpulse timing meets low
times. It is recommended that the first and last bits in the
frame be zero; this "encourages" SPI IPs to leave MOSI low
between frames.
config WS2812_STRIP_ZERO_FRAME
hex "SPI frame to shift out to signal a zero bit"
default 0x60
help
When shifted out at the configured clock frequency,
this must generate a pulse whose width fits within the chipset
specifications for T0H, and whose interpulse timing meets low
times. It is recommended that the first and last bits in the
frame be zero; this "encourages" SPI IPs to leave MOSI low
between frames.
# By default, we use GRBW [sic] (and ignore W).
comment "The following options determine channel data order on the wire."
config WS2812_RED_ORDER
int "Order in which a red pixel should be shifted out"
default 1
range 0 3
help
If the red channel is shifted out first, specify 0.
If second, specify 1, and so on.
config WS2812_GRN_ORDER
int "Order in which a green pixel should be shifted out"
default 0
range 0 3
help
If the green channel is shifted out first, specify 0.
If second, specify 1, and so on.
config WS2812_BLU_ORDER
int "Order in which a blue pixel should be shifted out"
default 2
range 0 3
help
If the blue channel is shifted out first, specify 0.
If second, specify 1, and so on.
config WS2812_HAS_WHITE_CHANNEL
bool "Does the chip have a white channel on wire?"
default y
help
If the chipset has a white channel, say y. White channels
are not used by the driver, but must be declared if expected
by the chip.
config WS2812_WHT_ORDER
int "Order in which a white pixel should be shifted out"
default 3
range 0 3
depends on WS2812_HAS_WHITE_CHANNEL
help
If the blue channel is shifted out first, specify 0.
If second, specify 1, and so on.
endif # WS2812_STRIP