Dmx interface for raspberry pi - Revision history

Rew: /* output mode */

2025-12-20T12:00:16Z

output mode

Rew: /* QLC+ */

2025-10-09T14:08:16Z

QLC+

Rew: /* DMX input on Linux */

2024-09-10T18:47:35Z

DMX input on Linux

Rew: /* Software */

2024-09-10T08:53:57Z

Software

Rew: /* bullseye */

2023-10-11T17:35:17Z

bullseye

Rew: /* bullseye */

2023-10-11T15:00:17Z

bullseye

Rew: /* bullseye */

2023-09-20T19:16:40Z

bullseye

Rew: /* OLA */

2023-09-20T19:09:41Z

OLA

Rew: /* output mode */

2023-09-20T18:49:21Z

output mode

Rew: /* all raspberries */

2023-09-20T18:43:08Z

all raspberries

@@ Line 204: / Line 204: @@
 ==== output mode ====
-Then set the board to output mode. I would recommend creating a small script (''sudo nano /usr/bin/set_dmx_mode; sudo chmod 755 /usr/bin/set_dmx_mode'') :
+Then set the board to output mode This is done by making GPIO18 an output and programming it to be high.
+The raspberries over the years have had various methods to influence the GPIO pins of the CPU running the show. In case they change it again it might be necessary to google for how to do it from now on. If you find I need to update this again, a tip is appreciated! (Thanks Richard!).
+On the most recent operating system releases, it seems you can configure the GPIO pin to be output-high, once and for all by adding:
+ gpio=18=op,dh
+to /boot/firmware/config.txt . On older OS releases:
+I would recommend creating a small script (''sudo nano /usr/bin/set_dmx_mode; sudo chmod 755 /usr/bin/set_dmx_mode'') :
  #!/bin/sh

@@ Line 36: / Line 36: @@
 === QLC+ ===
-Harold van Hulten wrote a nice "howto". See: http://www.udenix.nl/2016/how_did_i/rpi2dmx/
+Harold van Hulten wrote a nice "howto". .... link is dead :-( See: http://www.udenix.nl/2016/how_did_i/rpi2dmx/
 QLC+ 's home is at: http://www.qlcplus.org

@@ Line 21: / Line 21: @@
 == DMX input on Linux ==
-The Unix-derived way of handling tty/uart makes it impossible to do DMX input from userspace. So this option has existed in the hardware for ages, but for Linux there was no software support.
+The Unix-derived way of handling tty/uart makes it impossible to do DMX input from userspace. So this option has existed in the hardware for ages, but for Linux there was no software support for DMX input.
 I have recently  (september 2024) written a driver for the UART in userspace that will actually do DMX input and deliver the DMX universe as a memory mappable file. From there it is easy to export it say to OLA, and hopefully QLC+.
 This is a hardware driver, so it depends on the hardware. I've tested it on raspberry pi 3, and that works. I expect minor changes for other versions. It is not worth my trouble if nobody uses it, so if you need it, please let me know. I'll then make sure it works on YOUR raspberry pi and write some more documentation.
 == QLC+ and OLA ==

@@ Line 18: / Line 18: @@
 See: http://www.raspberrypi-dmx.com/
+== DMX input on Linux ==
+The Unix-derived way of handling tty/uart makes it impossible to do DMX input from userspace. So this option has existed in the hardware for ages, but for Linux there was no software support.
+I have recently  (september 2024) written a driver for the UART in userspace that will actually do DMX input and deliver the DMX universe as a memory mappable file. From there it is easy to export it say to OLA, and hopefully QLC+.
+This is a hardware driver, so it depends on the hardware. I've tested it on raspberry pi 3, and that works. I expect minor changes for other versions. It is not worth my trouble if nobody uses it, so if you need it, please let me know. I'll then make sure it works on YOUR raspberry pi and write some more documentation.

@@ Line 53: / Line 53: @@
 It seems that once again the stock OLA distribution has a problem with the uartdmx plugin.
+To simplify a few steps I recommend to just install ola from the distribution.
+We won't use the actual olad binary, but it arranges a few things that are useful.
+First this installs the scripts to have ola start at
+system boot. Also this will add the olad user we need to run the daemon under.
+We do this before compiling
+and installing ola from source so that our freshly compiled ola will overwrite
+the system binaries with a working one.
 To compile ola from scratch from the github current version first install the dependencies:
-Edit /etc/apt/sources.list
+If you haven't already done so, edit /etc/apt/sources.list
- nano  /etc/apt/sources.list
+ sudo nano  /etc/apt/sources.list
+and remove the # before deb-src, which is probably the third and last line. Then:
-and remove the # before deb-src, which is probably the third line. Then:
  sudo apt build-dep ola
 then get the sources:
   git clone https://github.com/OpenLightingProject/ola.git
+The ola deamon should run under user "olad". Adding that is simple enough:
+  sudo adduser --system olad
 Then configure, build and install:
@@ Line 74: / Line 90: @@
   sudo make install
-The build step will take about 20 minutes on a pi4 with a fast SD card. Next I had to add the olad user to the group tty to allow it to write to the device:
+The build step will take about 20 minutes on a pi4 with a fast SD card. (at least,
+that's what happened on mine :-) )
+Next I had to add the olad user to the group tty to allow it to write to the device:
   sudo adduser olad tty
-FYI: A non-working olad will report
+FYI: A non-working olad (the one in the bullseye distribution) will report
   plugins/uartdmx/UartWidget.cpp:180: Failed to set baud rate to 250k
 while a working one will report:
   plugins/uartdmx/UartDmxThread.cpp:136: Granularity for UART thread is GOOD
+Also FYI: The build in bullseye has defines and build flags that result in the baud-rate-setting
-Also FYI: I've compared the sources for the "working" distro-ola and the working-from-git and the only changes are documentation-related. Not a single line-of-code was changed between the two versions.
+code thinking that the calls needed to set the baud rate are not available. In the latest
+ola version the conditions that cause the code to think it isn't available have changed a bit
+and the "we can't change the baud rate because at compile time the calls weren't available"
+code now prints an error message instead of just returning: "couldn't change it for some reason"
+resulting in the above "failed to set baud rate" message without further explanation.
-If I've missed a step when you try this, let me know. (also let me know if all this was not necessary on your system, and say your distribution's ola worked).
+If I've missed a step when you try this, let me know.
+(also let me know if all this was not necessary on your system, and say your distribution's ola worked.
+This hopefully happens in a future debian/raspberry pi OS version).
 ==== stretch ====

@@ Line 155: / Line 155: @@
  sudo /usr/bin/set_dmx_mode 1
-I recommend putting that line in /etc/rc.local so that it gets executed at boot time so you don't have to worry about it. (IIRC there is an "exit 0" in there, so don't put it AFTER that!)
+I recommend putting that line in /etc/rc.local so that it gets executed at boot time so you don't have to worry about it. (there is an "exit 0" in there, so put it BEFORE that!)
-Or you can install the gpio utility from wiringpi and use the following command to view the status of all the pins
+Or you can install the gpio utility from wiringpi. However this now seems unmaintained and hard-to-get and possibly it doesn't even work on modern pi's. But if it works on your pi the following command allows you view the status of all the pins
  gpio readall
@@ Line 172: / Line 172: @@
-Note that the earlier versions of the DMX board have a bug that when the GPIO pin is an input (not driven) it will configure the board as an output. This is not desirable. Newer versions (starting 1.4) will have this "fixed" and the "default" will be "DMX IN" mode.
+Note that the earlier versions of the DMX board have a bug that when the GPIO 18 pin is an input (not driven) it will configure the board as an output. This is not desirable. Newer versions (starting 1.4) will have this "fixed" and the "default" will be "DMX IN" mode.
 This does mean that if you want the board to do output, you can get away with forgetting about this gpio18 business if you have an older version. (I just realized ''I'' was getting away with this.... :-) )

@@ Line 118: / Line 118: @@
 Most importantly: add:
  init_uart_clock=16000000
-to your config.txt file in the /boot directory.
+to your config.txt file in the /boot directory. In my tests today (2023) I had a different number on my screen when I was doing this. I used 3x more: 48000000. This works as well (on a rpi4).
 Next, you need to configure ola to use the native-uart plugin. It should be as easy as clicking on "add universe" on the ola home page. Somehow we often do not see the plugin active. Sometimes clicking on reload plugins helps, other times we need to restart ola to get the plugin to show up.