esp_dmx

This library allows for transmitting and receiving ANSI-ESTA E1.11 DMX-512A and transmitting ANSI-ESTA E1.20 RDM using an Espressif ESP32. It provides control and analysis of the packet configuration and allows the user to read or write synchronously or asynchronously from the DMX bus using whichever hardware UART port that is desired. This library also includes tools for data error-checking to safely process DMX and RDM commands as well as DMX packet metadata extraction to assist with troubleshooting errors.

Contents

• Library Installation
  • Arduino
  • ESP-IDF
  • PlatformIO
• Quick-Start Guide
• What is DMX?
  • What is RDM?
• DMX Basics
  • Addresses and the Start Code
  • Footprints
  • Universes
• RDM Basics
  • Unique IDs
  • Sub-devices
  • Parameters
  • Discovery
  • Response Types
• Configuring the DMX Port
  • Setting Communication Pins
  • Installing the Driver
  • Parameter Configuration
• Reading and Writing DMX
  • Reading DMX
  • DMX Sniffer
  • Writing DMX
• Reading and Writing RDM
  • RDM Requests
  • Discovering Devices
  • RDM Responder
• Error Handling
  • Timing Macros
  • DMX Start Codes
• Additional Considerations
  • Wiring an RS-485 Circuit
  • Currently Supported RDM PIDs
  • Hardware Specifications
• To Do

Library Installation

Arduino

This library requires the Arduino-ESP32 framework version 2.0.3 or newer. To install the correct framework, follow Espressif's instructions on the Arduino-ESP32 documentation page here.

This library can be installed by cloning this repository into your your Arduino/libaries folder or by searching for esp_dmx in the Arduino IDE Library Manager. Then simply include the library by adding #include "esp_dmx.h" at the top of your Arduino sketch.

ESP-IDF

This library requires ESP-IDF version 4.4.1 or newer. Clone this repository into your project's components folder. The library can be linked by writing #include "esp_dmx.h" at the top of your main.c file.

PlatformIO

This library is compatible with the PlatformIO IDE. Search for this library in the PlatformIO library registry and add it to your project. The library can be included by writing #include "esp_dmx.h" at the top of your main.c or main.cpp file.

Quick-Start Guide

To get started, call the following code in your setup() function if using Arduino, or app_main() in your main.c file if using ESP-IDF.

const dmx_port_t dmx_num = DMX_NUM_2;

// First set the communication pins...
const int tx_pin = 17;
const int rx_pin = 16;
const int rts_pin = 21;
dmx_set_pin(dmx_num, tx_pin, rx_pin, rts_pin);

// ...and then install the driver!
dmx_driver_install(dmx_num, DMX_DEFAULT_INTR_FLAGS);

To write data to the DMX bus, two functions are provided. The function dmx_write() writes data to the DMX buffer and dmx_send() sends the data out onto the bus. The function dmx_wait_sent() is used to block the task until the DMX bus is idle.

uint8_t data[DMX_PACKET_SIZE] = {0};

while (true) {
  // Write to the packet and send it.
  dmx_write(dmx_num, data, DMX_PACKET_SIZE);
  dmx_send(dmx_num, DMX_PACKET_SIZE);
  
  // Do work here...

  // Block until the packet is finished sending.
  dmx_wait_sent(dmx_num, DMX_TIMEOUT_TICK);
}

To read from the DMX bus, two additional functions are provided. The function dmx_receive() waits until a new packet has been received. The function dmx_read() reads the data from the driver buffer into an array so that it can be processed.

dmx_packet_t packet;
while (true) {
  const int size = dmx_receive(dmx_num, &packet, DMX_TIMEOUT_TICK);
  if (size > 0) {
    dmx_read(dmx_num, data, size);
    // Process data here...
  }

  // Do other work here...

}

That's it! For more detailed information on how this library works including details on RDM, keep reading.

What is DMX?

DMX is a unidirectional communication protocol used primarily in the entertainment industry to control lighting and stage equipment. DMX is transmitted as a continuous stream of packets using half-duplex RS-485 signalling with a standard UART port. DMX devices are typically connected using XLR5 in a daisy-chain configuration but other connectors such as XLR3 are common in consumer products.

Each DMX packet begins with a high-to-low transition called the break, followed by a low-to-high transition called the mark-after-break, followed by an eight-bit byte. This first byte is called the start code. The start-of-packet break, mark-after-break, and start code is called the reset sequence. After the reset sequence, a packet of up to 512 data bytes may be sent.

DMX imposes very strict timing requirements to allow for backwards compatibility with older lighting equipment. Frame rates may range from 1fps to up to approximately 830fps. A typical DMX controller transmits packets between approximately 25fps to 44fps. DMX receivers and transmitters have different timing requirements which must be adhered to carefully to ensure commands are processed.

Today, DMX often struggles to keep up with the demands of the latest hardware. Its low data rate and small packet size sees it losing market popularity over more capable protocols. However its simplicity and robustness often makes it the first choice for small scale projects.

For in-depth information on DMX, see the E1.11 standards document.

What is RDM?

RDM stands for Remote Device Management. It is an extension to the DMX protocol to allow intelligent, bidirectional communication between devices from multiple manufacturers utilizing a modified DMX data link. RDM permits a console or other controlling device to discover and then configure, monitor, and manage intermediate and end-devices connected through a DMX network.

When RDM capable devices must be configured but are inconveniently out of reach, it is said that RDM is "faster than the ladder." Instead of needing to climb a ladder to reach a device users are able to make changes to device settings from their DMX controller.

For in-depth information on RDM, see the E1.20 standards document.

DMX Basics

In a typical configuration, a DMX system consists of one DMX controller and up to 32 DMX fixtures per DMX port. A five-pin XLR cable, commonly known as a DMX cable, is connected to the DMX-out port of the DMX controller and into the the DMX-in port of the first DMX fixture. Each subsequent fixture is connected by a DMX cable between the DMX-out port of the previous fixture and the DMX-in port of the next fixture. A DMX terminator may be connected to the DMX-out port of the final fixture. This is only required when using RDM but can be helpful to ensure DMX signal stability when connecting more than 32 fixtures or for long runs of DMX cable.

Addresses and the Start Code

DMX addresses are needed for DMX controllers to communicate with fixtures. A fixture's address can be set between 1 and 512 (inclusive) by setting the fixture's DIP switches or by using the fixture's built-in display. DMX addresses correspond to DMX slots in a DMX packet. DMX address one is mapped to DMX packet slot one. Each DMX slot is an 8-bit number. A slot's minimum value is 0 and its maximum value is 255. To control a DMX dimmer set to DMX address five, DMX packet slot five must be written. To set the DMX dimmer to full intensity, slot five must be written to value 255. To set the dimmer to zero intensity, slot five must be written to value 0. Setting slot five to any value in between will dim the intensity appropriately.

Slot zero in the DMX packet is called the DMX start code. The start code informs DMX fixtures what type of packet is being sent. Standard DMX packets use a start code of 0x00, also called the null start code. DMX fixtures will not respond to DMX packets unless the packet begins with a null start code! A list of the other supported start codes can be found in the DMX start codes section.

Footprints

Many DMX fixtures support multiple controllable DMX parameters. Fixtures that support multiple parameters use multiple DMX addresses. An RGB LED fixture is a common example of a multi-parameter fixture. It uses three parameters: red, green, and blue. In this example, this fixture would therefore use three, consecutive DMX addresses. This is called the fixture's DMX footprint. The red, green, and blue parameters of an RGB LED fixture set to DMX address five can be controlled by writing to slots five, six, and seven, respectively. A fixture's DMX footprint can be found by reading its user manual. It is possible to address multiple DMX fixtures so that their DMX footprints overlap but this is uncommon.

Multi-parameter fixtures may support multiple footprints. On a fixture that supports multiple footprints, only one footprint can be active at a time. Larger footprints may be used to provide finer control of the fixture's DMX parameters. Conversely, smaller footprints may be used when finer control of a fixture is not needed. Instructions to change a fixture's active footprint may be found by consulting its user manual.

A fixture's DMX footprint may also be called a DMX personality, particularly when a fixture supports multiple footprints.

Universes

When more than 512 DMX addresses are used, it is required to use multiple DMX ports. Each DMX port is called a DMX universe. DMX fixtures can be uniquely identified by their DMX universe and address numbers. A common way to notate this is by separating the universe and address with a /. Therefore 3/475 represents universe three, address 475. It is important to understand that DMX fixtures are not aware of the concept of a universe. A fixture set to DMX address one will respond to writes to slot one on whichever universe to which it is connected.

RDM Basics

Compared to DMX, RDM is a fairly complex protocol which utilizes different packet and data types depending on the information that is being requested. This library attempts to abstract away many of the details of the RDM implementation to facilitate code ease-of-use while still providing a powerful feature set. The following sections are intended to provide a introduction to RDM as it pertains to this library. For a more comprehensive introduction of RDM, see the E1.20 standards document.

Unique IDs

In an RDM network, there is one controller device and several responder devices. Each device in the network has a Unique ID (UID) which uniquely identifies itself against others in the network. If an RDM device has multiple DMX ports, it may possess multiple UIDs; one for each DMX port. UIDs are 48-bits long. The most-significant 16-bits are a device's manufacturer ID. Devices made by the same manufacturer have the same most-significant 16-bits. The remaining, 32 least-significant-bits are a device's device ID. Readers may draw a reasonable comparison to MAC addresses in IP networking equipment. Every IP capable device has at least one MAC address and if they have multiple network interfaces they may have multiple MAC addresses. Similarly, the most significant bits in a MAC address identify a network interface's manufacturer.

UIDs are represented in text by displaying the UID in hexadecimal and by separating the manufacturer ID from the device ID with a :. If a device has a manufacturer ID with a value of 0xabcd and device ID with a value of 0x12345678, its full UID would be displayed as abcd:12345678.

When a controller device composes an RDM request, it must be addressed using a destination UID. The recipient of a request may be a single device, by using the device's UID, or multiple devices, by using a broadcast UID. Broadcast UIDs can be addressed to every device of a specific manufacturer or to all devices on the RDM network. To send a manufacturer broadcast, the destination UID's manufacturer ID must match the manufacturer ID of the desired manufacturer, and the device ID must be ffffffff. To broadcast to every device with the manufacturer ID of 05e0, the UID must be set to 05e0:ffffffff. The UID used to broadcast to all devices on the RDM network is ffff:ffffffff.

The lowest possible UID is 0000:00000000 and the highest possible UID is ffff:fffffffe. In practice the manufacturer IDs 0000 and ffff are not permitted so real-world RDM devices would never possess these UIDs. This library represents the maximum UID with the constant RDM_MAX_UID.

Organizations may apply for a unique manufacturer ID by contacting ESTA. The instructions to do so and a list of registered manufacturer IDs can be found here. This software library is registered and listed with the manufacturer ID of 05e0. Users of this library may use this manufacturer ID for their devices.

In this library, UIDs are represented with the rdm_uid_t type. The macro RDM_BROADCAST_MAN_UID() can be used to create a UID which broadcasts to the desired manufacturer ID and the constant RDM_BROADCAST_ALL_UID can be used to broadcast to all devices on the RDM network.

Sub-devices

Each RDM device may support up to 512 sub-devices. An example of a device that may support sub-devices is a dimmer rack which possesses multiple dimmers. Requests may be addressed to a specific dimmer in the dimmer rack by addressing the dimmer rack's UID, and specifying a sub-device number to target the appropriate dimmer.

The sub-device number which represents the root device is 0x0000. A request may also be addressed to all sub-devices of a root device by using the sub-device number 0xffff.

A root device and its sub-devices may support different RDM parameters, but each sub-device within a root device must support the same parameters as each other.

The constants RDM_ROOT_DEVICE and RDM_ALL_SUB_DEVICES are provided to improve code readability.

Parameters

RDM requests must be able to fetch and update parameters. The RDM standard specifies 52 different Parameter IDs (PIDs) which a device may support. The standard also specifies that manufacturers may define custom PIDs for their devices. The list of supported PIDs can be found here or in rdm_types.h.

Most PIDs can be either GET or SET if the responding device supports the requested PID. Some PIDs may support GET but do not support SET, and vice versa. Some PIDs may support both GET and SET. Three PIDs cannot be GET nor SET. These three PIDs are used for the RDM discovery algorithm. They are DISC_UNIQUE_BRANCH, DISC_MUTE, and DISC_UN_MUTE. RDM specifies that every device (but not its sub-devices necessarily) must support the following PIDs:

Parameter Name	GET	SET	Notes
DEVICE_INFO	X
DISC_MUTE
DISC_UN_MUTE
DISC_UNIQUE_BRANCH
DMX_START_ADDRESS	X	X	Support required if device uses a DMX slot.
IDENTIFY_DEVICE	X	X
PARAMETER_DESCRIPTION	X		Support required for manufacturer-specific PIDs.
SOFTWARE_VERSION_LABEL	X
SUPPORTED_PARAMETERS	X		Only required if supporting PIDs beyond the minimum set.

Discovery

When making RDM requests it is typically needed (but not required) to discover the UIDs of the devices on the RDM network. The discovery process begins by the controller device broadcasting a DISC_UNIQUE_BRANCH command to all devices. The data included in this request consist of an address space defined by a UID lower bound and UID upper bound. Responding devices respond to DISC_UNIQUE_BRANCH requests if their UID is greater-than-or-equal-to the lower bound and less-than-or-equal-to the upper bound. When multiple devices respond at the same time, data collisions can occur. When a data collision occurs, the controller divides the address space in two. A DISC_UNIQUE_BRANCH request is sent to each new address space. This is repeated until a single device is found within an address space.

When a single device is found within an address space, that device is sent a DISC_MUTE request to mute its response to future DISC_UNIQUE_BRANCH requests. When responding to DISC_MUTE requests, devices that have multiple UIDs return a binding UID which represents its primary UID.

Some RDM devices act as proxy devices. A proxy device is any inline device that acts as an agent or representative for one or more devices. A proxy device shall respond to all controller messages on behalf of the devices it represents as if it is the represented device. If a device is acting as a proxy device or if it is proxied by another device, it will indicate so in its response to DISC_MUTE and DISC_UN_MUTE requests.

Discovery should be performed periodically as discovered devices may be removed from the RDM network or new devices may be added. Before restarting the discovery algorithm, a DISC_UN_MUTE request should be broadcast to all devices in order to detect if devices were removed from the RDM network.

Response Types

Responding devices shall respond to requests only if the request was a non-broadcast request. Responding devices may respond to requests with the following response types:

• RESPONSE_TYPE_ACK indicates that the responder has correctly received the controller message and is acting upon the request.

• RESPONSE_TYPE_ACK_OVERFLOW indicates that the responder has correctly received the controller message and is acting upon the request, but there is more response data available than will fit in a single response packet. To receive the remaining information, controllers are able to send repeated requests to the same PID until the remaining information can fit in a single message.

• RESPONSE_TYPE_ACK_TIMER indicates that the responder is unable to supply the requested GET information or SET confirmation within the required response time. When sending this response, responding devices include an estimated response time that must elapse before the responder can provide the required information.

• RESPONSE_TYPE_NACK_REASON indicates that the responder is unable to reply with the requested GET information or unable to process the specified SET command. Responding devices must include a NACK reason code in their response. NACK reason codes are enumerated in the rdm_types.h header.

Responders must respond to every non-broadcast GET or SET request as well as every broadcast DISC_UNIQUE_BRANCH if their UID falls within the request's address space. When responding to DISC_UNIQUE_BRANCH requests, responders shall not send a DMX break and mark-after-break in order to improve discovery times and shall encode their response to reduce data loss during data collisions. Responders may only respond to DISC_MUTE and DISC_UN_MUTE requests with RESPONSE_TYPE_ACK.

Configuring the DMX Port

The DMX driver’s functions identify each of the UART controllers using dmx_port_t. This identification is needed for all the following function calls.

Setting Communication Pins

Configure the physical GPIO pins to which the DMX port will be connected. To do this, call the function dmx_set_pin() and specify which GPIO should be connected to the TX, RX, and RTS signals. If you want to keep a currently allocated pin to a specific signal, pass the macro DMX_PIN_NO_CHANGE. This macro should also be used if a pin isn't used.

// Set TX: GPIO16 (port 2 default), RX: GPIO17 (port 2 default), RTS: GPIO21.
dmx_set_pin(DMX_NUM_2, DMX_PIN_NO_CHANGE, DMX_PIN_NO_CHANGE, 21);

Installing the Driver

After the communication pins are set, install the driver by calling dmx_driver_install(). This function will allocate the necessary resources for the DMX driver. It instantiates the driver to default DMX settings. The following parameters are passed to this function:

• The DMX port to use.
• Flags to allocate interrupts. The macro DMX_DEFAULT_INTR_FLAGS can be used to allocate the interrupts using the default interrupt flags.

dmx_driver_install(DMX_NUM_2, DMX_DEFAULT_INTR_FLAGS);

Parameter Configuration

In most situations it is not necessary to adjust the default parameters of the DMX driver. Nevertheless, this library allows for individual configuration of the DMX baud rate, break, and mark-after-break. After the DMX driver has been installed, the following functions may be called.

dmx_set_baud_rate(DMX_NUM_2, DMX_BAUD_RATE);     // Set DMX baud rate.
dmx_set_break_len(DMX_NUM_2, DMX_BREAK_LEN_US);  // Set DMX break length.
dmx_set_mab_len(DMX_NUM_2, DMX_MAB_LEN_US);      // Set DMX MAB length.

If parameters values that are not within the DMX specification are passed to these functions, the values will be clamped so that they are within DMX specification. Note that it is possible to set driver parameters to be within DMX specification but not within RDM specification. Care must be used when using these functions to ensure that RDM capabilities are maintained.

The above functions each have _get_ counterparts to retrieve the currently set DMX parameters.

Reading and Writing DMX

DMX is a unidirectional protocol. This means that on the DMX bus only one device can transmit commands and many devices listen for commands. Therefore, this library permits either reading or writing to the bus but not both at once. If sending and receiving data concurrently is desired, users can use two UART ports and install a driver on each port.

Reading DMX

Reading may be performed synchronously or asynchronously from the DMX bus. It is typically desired to perform reads synchronously. This means that reads are only performed when a new DMX packet is received. This is ideal because it is not commonly desired to perform reads on the same data multiple times.

To read synchronously from the DMX bus the DMX driver must wait for a new packet. The blocking function dmx_receive() can be used for this purpose.

dmx_packet_t packet;
// Wait for a packet. Returns the size of the received packet or 0 on timeout.
int packet_size = dmx_receive(DMX_NUM_2, &packet, DMX_TIMEOUT_TICK);

The function dmx_receive() takes three arguments. The first argument is the dmx_port_t which identifies which DMX port to use. The second argument is a pointer to a dmx_packet_t struct. Data about the received packet is copied into the dmx_packet_t struct when a packet is received. This data includes:

• err reports any errors that occurred while receiving the packet (see: Error Handling).
• sc is the start code of the packet.
• size is the size of the packet in bytes, including the DMX start code. This value will never be higher than DMX_PACKET_SIZE.
• is_rdm evaluates to true if the packet is an RDM packet and if the RDM checksum is valid.

Using the dmx_packet_t struct is optional. If processing DMX or RDM packet data is not desired, users can pass NULL in place of a pointer to a dmx_packet_t struct.

The final argument to dmx_receive() is the amount of FreeRTOS ticks to block until the function times out. This library defines a constant, DMX_TIMEOUT_TICK, which is the length of time that must be waited until the DMX signal is considered lost according to DMX specification. According to DMX specification this constant is equivalent to 1250 milliseconds.

After a packet is received, dmx_read() can be called to read the packet into a user buffer. It is recommended to check for DMX errors before reading data but it is not required.

uint8_t data[DMX_PACKET_SIZE];

dmx_packet_t packet;
if (dmx_receive(DMX_NUM_2, &packet, DMX_TIMEOUT_TICK)) {

  // Check that no errors occurred.
  if (packet.err == ESP_OK) {
    dmx_read(DMX_NUM_2, data, packet.size);
  } else {
    printf("An error occurred receiving DMX!");
  }

} else {
  printf("Timed out waiting for DMX.");
}

There are two variations to the dmx_read() function. The function dmx_read_offset() is similar to dmx_read() but allows a small footprint of the entire DMX packet to be read.

const int size = 12;   // The size of this device's DMX footprint.
const int offset = 5;  // The start address of this device.
uint8_t data[size];

// Read slots 5 through 17. Returns the number of slots that were read.
int num_slots_read = dmx_read_offset(DMX_NUM_2, offset, data, size);

Lastly, dmx_read_slot() can be used to read a single slot of DMX data.

const int slot_num = 0;  // The slot to read. Slot 0 is the DMX start code!

// Read slot 0. Returns the value of the desired slot or -1 on error.
int value = dmx_read_slot(DMX_NUM_2, slot_num);

DMX Sniffer

This library offers an option to measure DMX break and mark-after-break timings of received data packets. This tool is much more resource intensive than the default DMX driver, so it must be explicitly enabled by calling dmx_sniffer_enable().

The DMX sniffer installs an edge-triggered interrupt on the specified GPIO pin. This library uses the ESP-IDF provided GPIO ISR which allows the use of individual interrupt handlers for specific GPIO interrupts. The interrupt handler works by iterating through each GPIO to determine if it triggered an interrupt and if so, it calls the appropriate handler.

A quirk of the default ESP-IDF GPIO ISR is that lower GPIO numbers are processed earlier than higher GPIO numbers. It is recommended that the DMX read pin be shorted to a lower GPIO number in order to ensure that the DMX sniffer can run with low latency.

It is important to note that the sniffer requires a fast clock speed in order to maintain low latency. In order to guarantee accuracy of the sniffer, the ESP32 must be set to a CPU clock speed of at least 160MHz. This setting can be configured in sdkconfig if the ESP-IDF is used.

Before enabling the sniffer tool, gpio_install_isr_service() must be called with the required DMX sniffer interrupt flags. The macro DMX_DEFAULT_SNIFFER_INTR_FLAGS can be used to provide the proper interrupt flags.

gpio_install_isr_service(DMX_DEFAULT_SNIFFER_INTR_FLAGS);

const int sniffer_pin = 4; // Lowest exposed pin on the Feather breakout board.
dmx_sniffer_enable(DMX_NUM_2, sniffer_pin);

Break and mark-after-break timings are reported to the DMX sniffer when it is enabled. To read data from the DMX sniffer call dmx_sniffer_get_data(). This will block until the sniffer receives a packet and copy the sniffer data so that it may be processed by the user. If data is copied, this function will return true.

dmx_metadata_t metadata;
if (dmx_sniffer_get_data(DMX_NUM_2, &metadata, DMX_TIMEOUT_TICK)) {
  printf("The DMX break length was: %i\n", metadata.break_len);
  printf("The DMX mark-after-break length was: %i\n", metadata.mab_len);
}

Writing DMX

To write to the DMX bus, dmx_write() can be called. This writes data to the DMX driver but it does not transmit a packet onto the bus. In order to transmit the data that was written, dmx_send() must be called.

uint8_t data[DMX_PACKET_SIZE] = { 0, 1, 2, 3 };

// Write the packet and send it out on the DMX bus.
const int num_bytes_to_send = DMX_PACKET_SIZE;
dmx_write(DMX_NUM_2, data, num_bytes_to_send);
dmx_send(DMX_NUM_2, num_bytes_to_send);

The size of the packet that is sent when calling dmx_send() can be specified in the second argument of the function. If the size is set to 0 then the size will be equal to either the size of the last call to dmx_write() or the slot number used in the last call to dmx_write_slot(), whichever is higher.

It takes a typical DMX packet approximately 22 milliseconds to send. During this time, it is possible to write new data to the DMX driver with dmx_write() if non-RDM data is being sent. To do so would result in an asynchronous write which may not be desired. To write data synchronously it is required to wait until the DMX packet is finished being sent. The function dmx_wait_sent() is used for this purpose.

uint8_t data[DMX_PACKET_SIZE] = { 0, 1, 2, 3 };

while (true) {
  // Send the DMX packet.
  dmx_send(DMX_NUM_2, DMX_PACKET_SIZE);

  // Process the next DMX packet (while the previous is being sent) here.
  for (int i = 1; i < DMX_PACKET_SIZE; i++) {
    data[i]++;  // Increment the value of each slot, excluding the start code.
  }

  // Wait until the packet is finished being sent before proceeding.
  dmx_wait_sent(DMX_NUM_2, DMX_TIMEOUT_TICK);

  // Now write the packet synchronously!
  dmx_write(DMX_NUM_2, data, DMX_PACKET_SIZE);
}

Individual DMX slots can be written using dmx_write_slot() similarly to reading individual slots with dmx_read_slot().

// Set slot number 5 to value 127.
const int slot_num = 5;
const uint8_t value = 127;
dmx_write_slot(DMX_NUM_2, slot_num, value);

// Don't forget to call dmx_send()!

Reading and Writing RDM

Using only the functions listed above it is possible to send and receive RDM packets. When an RDM packet is written using dmx_write() the DMX driver will respond accordingly and ensure that RDM timing requirements are met. For example, calls to dmx_send() typically send a DMX break and mark-after-break when sending a DMX packet with a null start code. When sending an RDM discovery response packet the DMX driver automatically removes the DMX break and mark-after-break which is required per the RDM standard. Sending RDM responses with dmx_send() may also fail when the DMX driver has detected that the RDM response timeout has already elapsed. This is done to reduce the number of data collisions on the RDM bus and keeps the RDM bus operating properly.

// This is a hard-coded discovery response packet!
const uint8_t discovery_response[] = {
 0xfe, 0xfe, 0xfe, 0xfe, 0xfe, 0xfe, 0xfe, 0xaa, 0xaf, 0x55, 0xea, 0xf5, 0xba, 
 0x57, 0xbb, 0xdd, 0xbf, 0x55, 0xba, 0xdf, 0xaa, 0x5d, 0xbb, 0x7d 
};
dmx_write(DMX_NUM_2, discovery_response, sizeof(discovery_response));

// This function will not send a DMX break or mark-after-break 
dmx_send(DMX_NUM_2, sizeof(discovery_response));

Likewise, the function dmx_receive() behaves contextually when receiving DMX or RDM packets. When receiving DMX, calls to dmx_receive() will timeout according to the timeout value provided, such as DMX_TIMEOUT_TICK. When receiving RDM packets, the DMX driver may timeout much more quickly than the provided timeout value as the RDM bus turnaround times are much shorter than DMX.

// This is a hard-coded DEVICE_INFO GET request!
const uint8_t get_device_info[] = {
  0xcc, 0x01, 0x18, 0x3b, 0x10, 0x44, 0xc0, 0x6f, 0xbf, 0x05, 0xe0, 0x12, 0x99,
  0x15, 0x9a, 0x14, 0x03, 0x00, 0x00, 0x00, 0x20, 0x00, 0x60, 0x00, 0x06, 0x38
};
dmx_write(DMX_NUM_2, get_device_info, sizeof(get_device_info));
dmx_send(DMX_NUM_2, sizeof(get_device_info));

dmx_packet_t packet;

// This function will unblock early because it is expecting a reply!
dmx_receive(DMX_NUM_2, &packet, DMX_TIMEOUT_TICK);  // Unblocks in 3ms

RDM Requests

This library currently supports the minimum required PIDs specified in the RDM standard. Request functions in this library are named using the prefix rdm_, whether the request is a GET or a SET, and the parameter name. To GET a device's DEVICE_INFO, users can call rdm_get_device_info(). To SET a device's DMX_START_ADDRESS, users can call rdm_set_dmx_start_address(). Functions which perform GET requests return the number of parameters it received from the responder. Functions which perform SET requests return true if a request was successful.

When printing UIDs to the terminal, the macros UIDSTR and UID2STR() can be used in printf-like functions.

rdm_uid_t uid = 0x3b1044c06fbf;  // The destination UID for the request.
rdm_response_t response;         // Stores response information.

rdm_device_info_t device_info;  // Stores the response parameter data.
int num_params = rdm_get_device_info(DMX_NUM_2, uid, RDM_ROOT_DEVICE, &response,
                                     &device_info);
if (num_params > 0) {
  printf("Successfully received device info!\n");
}

const int new_address = 123;  // The new DMX_START_ADDRESS to send.
bool success = rdm_set_dmx_start_address(DMX_NUM_2, uid, RDM_ROOT_DEVICE, 
                                         &response, new_address);
if (success) {
  printf("Device " UIDSTR " has been set to DMX address %i.\n", UID2STR(uid), 
         new_address);
}

Response information from requests is read into a rdm_response_t pointer which is provided by the user. Users can use this type to ensure that requests were successful and, if they are not successful, handle errors.

The response_type_t type contains the following fields:

• err evaluates to true if an error occurred reading DMX or RDM data. More information on error handling can be found in the Error Handling section.
• type is the type of the RDM response received. It can be any of the RDM response types enumerated in Response Types or RDM_RESPONSE_TYPE_NONE if no response was received.

The remaining response field is a union which should be read depending on the value in type.

• num_params should be read if type evaluates to RDM_RESPONSE_TYPE_ACK or RDM_RESPONSE_TYPE_ACK_OVERFLOW. It returns the number of RDM parameters that was received from the RDM responder.
• timer should be read if type evaluates to RDM_RESPONSE_TYPE_TIMER. It returns the number of FreeRTOS ticks that must elapse before the RDM responder will be ready to process the request.
• nack_reason should be read if type evaluates to RDM_RESPONSE_TYPE_NACK_REASON. It returns the NACK reason code that was received from the RDM responder.

Discovering Devices

This library provides two functions for performing full RDM discovery. The function rdm_discover_devices_simple() is provided as a simple implementation of the discovery algorithm which takes a pointer to an array of UIDs to store discovered UIDs and returns the number of UIDs found.

const int array_size = 10;
rdm_uid_t uids[array_size];

// This function blocks and may take some time to complete!
size_t num_uids = rdm_discover_devices_simple(DMX_NUM_2, uids, array_size);

Discovery can take several seconds to complete. Users may want to perform an action, such as update a progress bar, whenever a new UID is found. When this is desired, the function rdm_discover_with_callback() may be used to specify a callback function which is called when a new UID is discovered.

DISC_UNIQUE_BRANCH commands support neither GET nor SET. This PID request can be accessed with the function rdm_send_disc_unique_branch(). DISC_UNIQUE_BRANCH commands may only be sent to the root device, and may only be addressed to all devices on the RDM network. The sub_device and uid arguments have therefore been omitted from the function signature. This function is unique amongst the RDM functions provided by this library because it returns the decoded UID received from its response or 0 if no response was received. Due to the possibility of data collisions from this request, it is imperative that response.err is checked to verify data integrity.

// Define the address space within which devices will be discovered.
const rdm_disc_unique_branch_t disc_unique_branch = {
  .upper_bound = RDM_MAX_UID,
  .lower_bound = 0
};
rdm_response_t response;  // Stores response information.
rdm_uid_t uid = rdm_send_disc_unique_branch(DMX_NUM_2, &disc_unique_branch, 
                                            &response);
if (uid != 0) {
  // Got a DISC_UNIQUE_BRANCH response!

  if (response.err == ESP_OK) {
    // Only one device was found - print its UID.
    printf("Found the UID " UIDSTR ".\n", UID2STR(uid));
  } else if (response.err == ESP_ERR_INVALID_CRC) {
    // The checksum was invalid so a data collision occurred.
    printf("Multiple devices detected within this address space!\n");

    // Branch the address space here...
  )
} else {
  // If no reply was received, no new devices have been found.
  printf("No RDM devices were discovered in this address space.\n");
}

DISC_MUTE and DISC_UN_MUTE similarly do not support GET nor SET. These PIDs have been combined into one function, rdm_send_mute(). Muting or un-muting may be selected by providing the appropriate function argument, true to mute, false to un-mute. DISC_MUTE and DISC_UN_MUTE commands may only be sent to the root device, so the sub_device argument has been omitted from rdm_send_mute().

rdm_uid_t uid = RDM_BROADCAST_ALL_UID;  // Broadcast to all devices.
rdm_response_t response;                // Stores response information.

const bool MUTE = false;    // Send a DISC_UN_MUTE request.
rdm_disc_mute_t disc_mute;  // Store the response parameter data.
bool success = rdm_send_disc_mute(DMX_NUM_2, uid, MUTE, &response, &disc_mute);
if (success) {
  /* This code will never run because the RDM controller does not receive a 
    response from RDM responders when the destination UID is a broadcast UID. 
    Therefore its return value can be ignored and the function can be passed 
    NULL instead of an rdm_response_t pointer or an rdm_disc_mute_t pointer. */
}

RDM Responder

While it is currently possible to use this library as an RDM responder, no such user-friendly API to allow for convenient RDM response is exposed. This feature is currently in progress.

Error Handling

On rare occasions, DMX packets can become corrupted. Errors are typically detected upon initially connecting to an active DMX bus but are resolved on receiving the next packet. Errors can be checked by reading the error code from the dmx_packet_t struct. The error types are as follows:

• ESP_OK indicates data was read successfully.
• ESP_ERR_TIMEOUT indicates that the driver timed out waiting for a packet.
• ESP_FAIL occurs when the DMX driver detects missing stop bits. If this condition occurs, the driver shall discard the improperly framed slot data and all following slots in the packet. When this error is reported the dmx_packet_t size can be read to determine at which slot the error occurred.
• ESP_ERR_NOT_FINISHED occurs when the ESP32 hardware overflows resulting in loss of data.

uint8_t data[DMX_PACKET_SIZE];

dmx_packet_t packet;
while (true) {
  if (dmx_receive(DMX_NUM_2, &packet, DMX_TIMEOUT_TICK)) {
    switch (packet.err) {
      case ESP_OK:
        printf("Received packet with start code: %02X and size: %i.\n",
          packet.sc, packet.size);
        // Data is OK. Now read the packet into the buffer.
        dmx_read(DMX_NUM_2, data, packet.size);
        break;
      
      case ESP_ERR_TIMEOUT:
        printf("The driver timed out waiting for the packet.\n");
        /* If the provided timeout was less than DMX_TIMEOUT_TICK, it may be
          worthwhile to call dmx_receive() again to see if the packet could be
          received. */
        break;

      case ESP_FAIL:
        printf("Received malformed byte at slot %i.\n", packet.size);
        /* A slot in the packet is malformed. Data can be recovered up until 
          packet.size. */
        break;

      case ESP_ERR_NOT_FINISHED:
        printf("The DMX port overflowed.\n");
        /* The ESP32 UART overflowed. This could occur if the DMX ISR is being
          constantly preempted. */
        break;
    }
  } else {
    printf("Lost DMX signal.\n");
    // A packet hasn't been received in DMX_TIMEOUT_TICK ticks.

    // Handle packet timeout here...
  }
}

When an RDM responder receives a non-broadcast packet addressed to it, it must respond with a properly formatted response packet. Packets may become lost or corrupted due to poor bus conditions or due to poorly-made RDM devices. Many devices are advertised as being RDM compliant but may not be. Non-compliant devices are often sold by third-party manufacturers or by knock-off imitation brands. Some RDM commands may work on non-compliant devices, but others may not.

To determine if an RDM error occurred, the error code in rdm_response_t can be read.

• ESP_ERR_INVALID_RESPONSE occurs when an RDM response was improperly formatted.
• ESP_ERR_INVALID_CRC indicates that the computed checksum does not match the checksum received in the RDM packet.
• ESP_ERR_NOT_SUPPORTED indicates that an RDM RESPONSE_TYPE_ACK_OVERFLOW response was received. This response is valid for some RDM commands but is not currently supported by this library.

Receiving any other error code in the rdm_response_t indicates an error receiving DMX data. The appropriate error condition can be determined by referencing the DMX error codes listed above.

Timing Macros

It should be noted that this library does not automatically check for DMX timing errors. This library does provide macros to assist with timing error checking, but it is left to the user to implement such measures. DMX and RDM each have their own timing requirements so macros for checking DMX and RDM are both provided. The following macros can be used to assist with timing error checking.

• DMX_BAUD_RATE_IS_VALID() evaluates to true if the baud rate is valid for DMX.
• DMX_BREAK_LEN_IS_VALID() evaluates to true if the DMX break duration is valid.
• DMX_MAB_LEN_IS_VALID() evaluates to true if the DMX mark-after-break duration is valid.
• RDM_BAUD_RATE_IS_VALID() evaluates to true if the baud rate is valid for RDM.
• RDM_BREAK_LEN_IS_VALID() evaluates to true if the RDM break duration is valid.
• RDM_MAB_LEN_IS_VALID() evaluates to true if the RDM mark-after-break duration is valid.

DMX and RDM specify different timing requirements for receivers and transmitters. This library attempts to simplify error checking by combining timing requirements for receiving and transmitting. Therefore there are only the above six timing error checking macros instead of six macros each for receiving and transmitting.

DMX Start Codes

This library offers the following macro constants for use as DMX start codes. More information about each start code can be found in the DMX standards document or in dmx_types.h.

• DMX_SC is the standard DMX null start code.
• RDM_SC is the standard Remote Device Management start code.
• DMX_TEXT_SC is the ASCII text start code.
• DMX_TEST_SC is the test packet start code.
• DMX_UTF8_SC is the UTF-8 text packet start code.
• DMX_ORG_ID_SC is the organization/manufacturer ID start code.
• DMX_SIP_SC is the System Information Packet start code.

Additional macro constants include the following:

• RDM_SUB_SC is the sub-start code for Remote Device Management. It is the first byte received after the RDM start code.
• RDM_PREAMBLE is not considered a start code but is often the first byte received in an RDM discovery response packet.
• RDM_DELIMITER is not considered a start code but is the delimiter byte received at the end of an RDM discovery response preamble.

Some start codes are considered invalid and should not be used in a DMX packet. The validity of the start code can be checked using the macro DMX_START_CODE_IS_VALID(). If the start code is valid, this macro will evaluate to true. This library does not automatically check for valid start codes. Such error checking is left to the user to implement.

Additional Considerations

Wiring an RS-485 Circuit

DMX is transmitted over RS-485. RS-485 uses twisted-pair, half-duplex, differential signalling to ensure that data packets can be transmitted over large distances. DMX starts as a UART signal which is then driven using an RS-485 transceiver. Because the ESP32 does not have a built-in RS-485 transceiver, it is required for the ESP32 to be wired to a transceiver in most cases.

RS-485 transceivers typically have four data input pins: RO, DI, DE, and /RE. RO is receiver output. It is the pin that the UART RX pin is connected to so that data may be read from other devices to the ESP32. DI is driver input. It is connected to the UART TX pin so that data may be written to other devices from the ESP32. DE is driver input enable. Bringing this pin high enables the input on the DI pin. /RE is receiver output enable. The overline on this pin name indicates that it is active when driven low, and inactive when driven high. Driving this pin low enables the input on the DI pin.

Because DE and /RE enable writing and reading respectively, and because DE is active high and /RE is active low, these pins are often shorted together. In this example, these pins are wired together and are controlled with one pin on the ESP32. This pin is called the enable pin. It can also be referred to as the RTS pin. The example schematic can be seen below.

In this example circuit, R1 and R3 are 680 ohms each. Many RS-485 breakout boards set these resistor values to 20k ohm or higher. Such high resistance values are acceptable and should still allow DMX to be written and read.

R2, the 120 ohm resistor, is a terminating resistor. It is required only when using RDM. Including this resistor in schematics can also ensure system stability when connecting long lines of DMX consisting of multiple devices. If it is decided not to include this resistor, DMX-A and DMX-B should not be shorted together.

Many RS-485 chips, such as the Maxim MAX485 are 3.3v tolerant. This means that it can be controlled with the ESP32 without any additional electrical components. Other RS-485 chips may require 5v data to transmit DMX. In this case, it is required to convert the output of the ESP32 to 5v using a logic level converter.

Currently Supported RDM PIDs

The PIDs currently implemented by this library are listed below.

Parameter	GET	SET	Notes
DEVICE_INFO	X
DISC_MUTE			DISC_MUTE and DISC_UN_MUTE combined into one function.
DISC_UN_MUTE			DISC_MUTE and DISC_UN_MUTE combined into one function.
DISC_UNIQUE_BRANCH
DMX_START_ADDRESS	X	X
IDENTIFY_DEVICE	X	X
SOFTWARE_VERSION_LABEL	X
SUPPORTED_PARAMETERS	X		RESPONSE_TYPE_ACK_OVERFLOW not currently supported.

Hardware Specifications

ANSI-ESTA E1.11 DMX512-A specifies that DMX devices be electrically isolated from other devices on the DMX bus. In the event of a power surge, the likely worse-case scenario would mean the failure of the RS-485 circuitry and not the entire DMX device. Some DMX devices may function without isolation, but using non-isolated equipment is not recommended.

To Do

For a list of planned features, see the esp_dmx GitHub Projects page.