Hey,

some time ago i contributed support for APA102 LEDs to OLA.
i based most of the things on the wounder full reverse engineering of Tim’s Blog.
while writing the code i made some tests that i documented in the Pull-Request on Github.

Now my PR is merged and i want to make some additional test about timing and so on:

I followed the Tutorial ‘OLA on Raspberry Pi’ with the ‘GIT Repo Image’ option and compiled ola with this config

./configure --enable-python-libs --enable-rdm-tests

.
this takes some hours – to speed up you can use

./configure --disable-all-plugins --enable-python-libs --enable-dummy --enable-spi

so only python dummy and spi is enabled.

My Test-Setup:

i have 25 physical Pixels connected. first the short 5pixel Strip and than the 20PixelStrip.

i have written a simple python scirpt to test things.
it generates a ‘strobe’ effect – on frame on on frame off.
you can find it on github in my ‘script collection’

the script allows two arguments: ‘TICK_INTERVAL’ and ‘pixel_count’.
copy the script to your home folder on rpi ( i used FireFTP – but there are other ways to do this..)

first start olad –> ‘olad -l 3’
then you can start the script with ‘python ./strobe.py 25 170’ the 25 is the Intervall and the 170 the pixels to send data for. the script connects to universe 5. (you can change it in the code if you like..)
to exit the script use Ctrl+C

in the ‘~/.ola/ola-spi.conf’ you can setup the spi-baudrate and other things.
mine looked like this:

base_uid = 7a70:00000100
device_prefix = spidev
enabled = true
spidev0.0-0-device-label = MyTest
spidev0.0-0-dmx-address = 1
spidev0.0-0-personality = 7
spidev0.0-0-pixel-count = 170
spidev0.0-backend = software
spidev0.0-ports = 1
spidev0.0-spi-ce-high = false
spidev0.0-spi-speed = 1000000
spidev0.0-sync-port = 0
spidev0.1-0-device-label = SPI Device - spidev0.1
spidev0.1-0-dmx-address = 1
spidev0.1-0-personality = 7
spidev0.1-0-pixel-count = 170
spidev0.1-backend = software
spidev0.1-ports = 1
spidev0.1-spi-ce-high = false
spidev0.1-spi-speed = 1000000
spidev0.1-sync-port = 0

so in this example the spi-speed is set to 1000000Hz = 1000kHz = 1MHz

i made a series of tests / meassurements and changed this parameters:

• spi-speed
• pixel-count (changed this at both points – in the config and the script)
• TICK_INTERVAL

i measured with my relative old HAMEG HM407 Analog/Digital Scope (40MHz 100MS/s)

conclusion:
with 1020 Pixel (6 full Universes) i am getting the error

plugins/spi/SPIWriter.cpp:118: Failed to write all the SPI data: Message too long

so i used a 1000Pixels as maximum.

with 7,7MHz its possible to use 1000Pixels and get an update rate of about 35Hz.

Here the full Table: 🙂