diff options
| -rw-r--r-- | decoders/rgb_led_ws281x/pd.py | 28 |
1 files changed, 28 insertions, 0 deletions
diff --git a/decoders/rgb_led_ws281x/pd.py b/decoders/rgb_led_ws281x/pd.py index 7c8ead4..3e66dac 100644 --- a/decoders/rgb_led_ws281x/pd.py +++ b/decoders/rgb_led_ws281x/pd.py @@ -17,6 +17,34 @@ ## along with this program; if not, see <http://www.gnu.org/licenses/>. ## +# Implementor's notes on the wire format: +# - World Semi vendor, (Adafruit copy of the) datasheet +# https://cdn-shop.adafruit.com/datasheets/WS2812.pdf +# - reset pulse is 50us (or more) of low pin level +# - 24bits per WS281x item, 3x 8bits, MSB first, GRB sequence, +# cascaded WS281x items, all "excess bits" are passed through +# - bit time starts with high period, continues with low period, +# high to low periods' ratio determines bit value, datasheet +# mentions 0.35us/0.8us for value 0, 0.7us/0.6us for value 1 +# (huge 150ns tolerances, un-even 0/1 value length, hmm) +# - experience suggests the timing "is variable", rough estimation +# often is good enough, microcontroller firmware got away with +# four quanta per bit time, or even with three quanta (30%/60%), +# Adafruit learn article suggests 1.2us total and 0.4/0.8 or +# 0.8/0.4 high/low parts, four quanta are easier to handle when +# the bit stream is sent via SPI to avoid MCU bit banging and its +# inaccurate timing (when interrupts are used in the firmware) +# - RGBW datasheet (Adafruit copy) for SK6812 +# https://cdn-shop.adafruit.com/product-files/2757/p2757_SK6812RGBW_REV01.pdf +# also 1.2us total, shared across 0.3/0.9 for 0, 0.6/0.6 for 1, +# 80us reset pulse, R8/G8/B8/W8 format per 32bits +# - WS2815, RGB LED, uses GRB wire format, 280us RESET pulse width +# - more vendors and models available and in popular use, +# suggests "one third" or "two thirds" ratio would be most robust, +# sample "a little before" the bit half? reset pulse width may need +# to become an option? matrices and/or fast refresh environments +# may want to experiment with back to back pixel streams + import sigrokdecode as srd from common.srdhelper import bitpack_msb |