This library allows for transmitting and receiving ANSI-ESTA E1.11 DMX-512A 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 commands as well as DMX packet metadata extraction to assist with troubleshooting DMX errors.
- Library Installation
- Quick-Start Guide
- What is DMX?
- Configuring the DMX Port
- Reading and Writing
- Error Handling
- Additional Considerations
- To Do
This library requires the Arduino-ESP32 framework version 2.0.0 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 and installing the desired version. Then simply include the library by adding #include "esp_dmx.h" at the top of your Arduino sketch.
Clone this repository into your project's components folder. The library can be linked by putting #include "esp_dmx.h" at the top of your main.c file.
This library is compatible with the PlatformIO IDE. PlatformIO does not currently support Arduino-ESP32 v2.0.0 by default. Therefore, when using the Arduino framework on PlatformIO, it is required to adjust your default platformio.ini to enable this library to compile. Simply change the platform specified in platformio.ini from espressif32 to https://github.com/platformio/platform-espressif32.git#feature/arduino-upstream. This instructs PlatformIO to download Arduino-ESP32 v2.0.0 from its repository which may take some time, typically about 15 minutes. No such changes are necessary when using ESP-IDF on PlatformIO.
This library was written to look similar to the ESP-IDF UART implementation. 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 configure the UART...
const dmx_config_t config = DMX_DEFAULT_CONFIG;
dmx_param_config(dmx_num, &config);
// then set the communication pins...
const int tx_io_num = 17, rx_io_num = 16, rts_io_num = 21;
dmx_set_pin(dmx_num, tx_io_num, rx_io_num, rts_io_num);
// and install the driver!
QueueHandle_t dmx_queue;
dmx_driver_install(dmx_num, DMX_MAX_PACKET_SIZE, 10, &dmx_queue,
ESP_INTR_FLAG_IRAM);Before the user is able to write to the DMX bus, the driver mode must be set. Call dmx_set_mode() and pass either DMX_MODE_RX or DMX_MODE_TX. After the driver is installed DMX_MODE_RX is the default.
// configure for tx
dmx_set_mode(dmx_num, DMX_MODE_TX);To write data to the DMX bus, two functions are provided. The function dmx_write_packet() writes data to the DMX buffer and dmx_tx_packet() sends the data out onto the bus. The function dmx_wait_tx_done() is used to block the task until the DMX bus is idle.
uint8_t data[DMX_MAX_PACKET_SIZE] = {0};
while (1) {
// write to the packet and tx it
dmx_write_packet(dmx_num, data, DMX_MAX_PACKET_SIZE);
dmx_tx_packet(dmx_num);
// do work here...
// block until the packet is finished sending
dmx_wait_tx_done(dmx_num, DMX_TX_PACKET_TOUT_TICK);
}To read from the DMX bus, use the queue handle passed to dmx_driver_install(). The function dmx_read_packet() is provided to read from the driver buffer into an array.
dmx_event_t event;
while (1) {
if (xQueueReceive(dmx_queue, &event, DMX_RX_PACKET_TOUT_TICK)) {
// read the packet from the driver buffer into 'data'
dmx_read_packet(dmx_num, data, DMX_MAX_PACKET_SIZE);
}
// do other work here...
}That's it! For more detailed information on how this library works, keep reading.
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.
Configuring and setting up the DMX driver should be familiar to those who have experience with the ESP-IDF UART driver. The functions dmx_param_config(), dmx_set_pin(), and dmx_driver_install() have similar behavior to uart_param_config(), uart_set_pin(), and uart_driver_install().
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.
Call the function dmx_param_config() and pass it a dmx_config_t structure. It contains all the parameters needed to configure the DMX packet settings. In most situations, custom packet configuration isn't necessary. The macro DMX_DEFAULT_CONFIG is provided to simplify this process.
const dmx_config_t dmx_config = DMX_DEFAULT_CONFIG;
dmx_param_config(DMX_NUM_2, &dmx_config);If using a custom DMX configuration is desired, the dmx_config_t parameters can be set manually.
const dmx_config_t dmx_config = {
.baud_rate = 250000, // typical baud rate
.break_num = 45, // 180us
.idle_num = 5 // 20us
};
dmx_param_config(DMX_NUM_2, &dmx_config);The break_num corresponds to the duration of the packet break and idle_num corresponds to the duration of the mark after break. Both values are set in units of time that it takes to send one bit at the current baud rate. If the current baud rate is 250k, it takes 4μs to send one bit. Setting break_num to 45 and idle_num to 5 in this example sets the break and mark after break to 180μs and 20μs respectively.
Parameters may be configured individually by calling the below dedicated functions. These functions are also useful if re-configuring a single parameter.
dmx_set_baud_rate(DMX_NUM_2, 250000);
dmx_set_break_num(DMX_NUM_2, 44);
dmx_set_idle_num(DMX_NUM_2, 3);Each of the above functions has a _get_ counterpart to check the currently set value. For example, to check the current baud rate, call dmx_get_baud_rate().
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: IO16 (port 2 default), RX: IO17 (port 2 default), RTS: IO21
dmx_set_pin(DMX_NUM_2, DMX_PIN_NO_CHANGE, DMX_PIN_NO_CHANGE, 21);After the communication pins are set, install the driver by calling dmx_driver_install(). The following parameters are passed to this function:
- Size of the driver double-buffer
- Size of the event queue
- Handle to the queue
- Flags to allocate interrupts
This function will allocate the necessary resources for the DMX driver. Note that the driver uses a double-buffer system. The driver will allocate twice the size of the passed buffer size argument.
QueueHandle_t dmx_queue;
const int buffer_size = DMX_MAX_PACKET_SIZE; // 513 bytes
// install DMX driver using an event queue
dmx_driver_install(DMX_NUM_2, buffer_size, 10, &dmx_queue, 0);Once this step is complete, DMX devices can be connected to check for communication.
DMX is a unidirectional protocol. This means that on the DMX bus only one device can transmit commands and many devices (typically up to 32) listen for commands. Therefore, this library permits either reading or writing to the bus but not both at once.
To set the driver mode call dmx_set_mode() and pass to it either DMX_MODE_RX or DMX_MODE_TX. After the driver is installed DMX_MODE_RX is the default.
// set the DMX driver to transmit mode
dmx_set_mode(DMX_NUM_2, DMX_MODE_TX);
// dmx_set_mode(DMX_NUM_2, DMX_MODE_RX); // don't need to rx nowIf transmitting and receiving data simultaneously is desired, the user can install two drivers on two UART ports. It should be noted that this is an unusual use case. This library is not meant to act as a DMX optoisolator or splitter.
To read from the DMX bus, the event queue handle passed to dmx_driver_install() can be used to determine when a packet has been received. A dmx_event_t message will be posted to the event queue. Then the packet can be read from the DMX driver double-buffer into a user buffer using dmx_read_packet().
The macro DMX_RX_PACKET_TOUT_TICK can be used to block the task until a packet is received or a DMX timeout occurs.
// allocate a buffer that is the max size of a DMX packet
uint8_t data[DMX_MAX_PACKET_SIZE];
dmx_event_t event;
while (1) {
if (xQueueReceive(dmx_queue, &event, DMX_RX_PACKET_TOUT_TICK) == pdTRUE) {
// read back the size of the packet into our buffer
dmx_read_packet(DMX_NUM_2, data, event.size);
} else {
// handle packet timeout...
}
}The dmx_event_t structure contains some helpful information about the packet that was received. Some of the information includes:
- Packet errors
- Start code
- Size in bytes
- Duration in microseconds
These values can be used to determine if the received data should be processed or ignored.
// if there are no errors and the start code is correct, read the packet
if (event.status == DMX_OK && event.start_code == DMX_SC) {
dmx_read_packet(DMX_NUM_2, data, event.size);
printf("Packet took %i microseconds!", event.duration);
}Individual DMX slots can be read using dmx_read_slot(). To verify that the DMX slot exists, the size of the packet should be verified.
const int slot_idx = 5;
if (event.status == DMX_OK && event.size >= slot_idx) {
uint8_t slot_data;
dmx_read_slot(DMX_NUM_2, slot_idx, &slot_data);
printf("Slot %i == %i", slot_idx, slot_data);
}This library offers tools to perform robust error-checking. For more information on errors, see the Error Handling section.
This library offers an option to measure break and mark after break timings of received data packets. This tool is much more resource intensive than the default DMX receive driver, so it must be explicitly enabled by calling dmx_rx_timing_enable().
The timing tool 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 RX pin be shorted to a lower GPIO number in order to ensure that the DMX timing tool can run with low latency.
It is important to note that the timing tool requires a fast clock speed in order to maintain low latency. In order to guarantee accuracy of the timing tool, 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 timing analysis tool gpio_install_isr_service() must be called.
gpio_install_isr_service(ESP_INTR_FLAG_EDGE | ESP_INTR_FLAG_IRAM);
const int timing_io_num = 4; // lowest exposed pin on the Feather breakout board
dmx_rx_timing_enable(DMX_NUM_2, timing_io_num);Break and mark after break timings are reported to the event queue when the timing tool is enabled. If the timing tool is disabled, either because dmx_rx_timing_disable() was called or because dmx_rx_timing_enable() was not called, the reported break and mark after break durations will default to -1.
dmx_event_t event;
if (xQueueReceive(queue, &event, DMX_RX_PACKET_TOUT_TICK) == pdTRUE) {
// read back break and mark after break
printf("The break was %ius, ", event.timing.brk);
printf("and the mark after break was %ius.\n", event.timing.mab);
}Writing to the DMX bus does not require the use of an event queue. To write to the DMX bus, dmx_write_packet() 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_tx_packet() can be called. When a packet is sent out onto the bus, its size will be the same as the buffer size that was passed to dmx_driver_install().
uint8_t data[DMX_MAX_PACKET_SIZE] = { 0, 1, 2, 3 };
dmx_set_mode(DMX_NUM_2, DMX_MODE_TX); // enable tx mode
// write the packet and send it out on the DMX bus
dmx_write_packet(DMX_NUM_2, data, MAX_PACKET_SIZE);
dmx_tx_packet(DMX_NUM_2);Calling dmx_tx_packet() will fail if the DMX driver is currently transmitting a packet of DMX data. To ensure that packets are continuously sent, dmx_wait_tx_done() can be used.
uint8_t data[DMX_MAX_PACKET_SIZE] = { 0, 1, 2, 3 };
dmx_set_mode(DMX_NUM_2, DMX_MODE_TX); // enable tx mode
while (1) {
// write and send the packet
dmx_write_packet(DMX_NUM_2, data, MAX_PACKET_SIZE);
dmx_tx_packet(DMX_NUM_2);
// do other work here...
// block until we are ready to send another packet
dmx_wait_tx_done(DMX_NUM_2, DMX_TX_PACKET_TOUT_TICK);
}The DMX driver will automatically check if the DMX transmission has timed out between sending the last packet and the current packet. If it has, it will simulate a DMX reset sequence in software before sending a new packet. Simulating the reset sequence uses inefficient busy-waiting to recreate a break and mark after break. ESP32 busy-waiting is imprecise at the microsecond resolution that is needed for the reset sequence. If the DMX task is not preempted it is usually precise within 30μs. Because this should only happen after sending the first packet and because 30μs is well within DMX timing requirements, this behavior is acceptable for this library.
Individual DMX slots can be written using dmx_write_slot().
// set slot 5 to 127
const int slot_idx = 5;
uint8_t slot_val = 127;
dmx_write_slot(DMX_NUM_2, slot_idx, slot_val);
// don't forget to call dmx_tx_packet()!On rare occasions, DMX packets can become corrupted. Errors can be checked by reading the status from the dmx_event_t structure. The error types are as follows:
DMX_OKoccurs when the packet is received successfully.DMX_ERR_IMPROPER_SLOToccurs when a slot is missing a start or stop bit.DMX_ERR_PACKET_SIZEoccurs when the number of data bytes received exceedsDMX_MAX_PACKET_SIZEDMX_ERR_BUFFER_SIZEoccurs when the driver buffer size is smaller than the number of packets received. This error will not occur if the driver buffer size is set toDMX_MAX_PACKET_SIZE.DMX_ERR_DATA_OVERFLOWoccurs when the UART hardware is not able to process data quickly enough and it overflows.
In most errors, the event size can be read to determine at which byte the error occurred. In every error condition except for DMX_ERR_BUFFER_SIZE the event start code will default to -1.
dmx_event_t event;
while (1) {
if (xQueueReceive(queue, &event, DMX_RX_PACKET_TOUT_TICK)) {
switch (event.status) {
case DMX_OK:
printf("Received packet with start code: %02X and size: %i\n",
event.start_code, event.size);
// data is ok - read the packet into our buffer
dmx_read_packet(DMX_NUM_2, data, event.size);
break;
case DMX_ERR_IMPROPER_SLOT:
printf("Received malformed byte at slot %i\n", event.size);
// a slot in the packet is malformed - possibly a glitch due to the
// XLR connector? will need some more investigation
// data can be recovered up until event.size
break;
case DMX_ERR_PACKET_SIZE:
printf("Packet size %i is invalid\n", event.size);
// the host DMX device is sending a bigger packet than it should
// data may be recoverable but something went very wrong to get here
break;
case DMX_ERR_BUFFER_SIZE:
printf("User DMX buffer is too small - received %i slots\n",
event.size);
// whoops - our buffer isn't big enough
// this code will not run if buffer size is set to DMX_MAX_PACKET_SIZE
break;
case DMX_ERR_DATA_OVERFLOW:
printf("Data could not be processed in time\n");
// the UART FIFO overflowed
// this could occur if the interrupt mask is misconfigured or if the
// DMX ISR is constantly preempted
break;
}
} else {
printf("Lost DMX signal\n");
// haven't received a packet in DMX_RX_PACKET_TOUT_TICK ticks
// handle packet timeout...
}
}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. The following macros can be used to assist with timing error checking.
DMX_RX_PKT_DURATION_IS_VALID()evaluates to true if the packet duration is valid.DMX_RX_BRK_DURATION_IS_VALID()evaluates to true if the break duration is valid.DMX_RX_MAB_DURATION_IS_VALID()evaluates to true if the mark after break duration is valid.
DMX specifies different timing requirements for receivers and transmitters. In situations where it is necessary to check if transmitted timing values are valid, this library provides _TX_ versions of the above macros.
Finally, the following macros can be used in both transmit and receive scenarios.
DMX_BAUD_RATE_IS_VALID()evaluates to true if the baud rate is valid.DMX_START_CODE_IS_VALID()evaluates to true if the start code is permitted in the DMX standard.
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_caps.h.
DMX_SCis the standard DMX null start code.RDM_SCis the standard Remote Device Management start code.DMX_TEXT_ASCis the ASCII text alternate start code.DMX_TEST_ASCis the test packet alternate start code.DMX_UTF8_ASCis the UTF-8 text packet alternate start code.DMX_ORG_ID_ASCis the organization/manufacturer ID alternate start code.DMX_SIP_ASCis the System Information Packet alternate start code.
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.
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.
Currently, implementation of Remote Device Management (RDM) is not planned. The primary reason for this is because the author of this library does not have access to any lighting devices that support RDM, so it is difficult to test RDM compatibility. The secondary reason is because this library supports DMX at a low level of abstraction. RDM is relatively higher level than DMX. This means that RDM can be implemented using this library, but to implement RDM as an API of this library is beyond the scope of this library.
- Add RS-485 example circuit to the readme
- Reset-Sequence-First Mode. Allow for reset sequences to be sent first rather than using the UART hardware break circuitry.
- Allow for use of ESP32 Hardware Timer for Reset Sequence.
- Allow for users to increase ESP32 UART Hardware FIFO?
- Allow for use of UART DMA?
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