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Prelude - Development Application | Prelude User's Guide


Prelude is a program for controlling the LL-RLP-20 and/or LL-RXR-27 USB-UART evaluation boards. The program allows users quickly to start sending and receiving messages using the Symphony Link system. The software offers a graphical representation of the behavior of Link Labs' family of Symphony Link Modules as connections are established and messages are sent and received.

Prelude can control the LL-RLP-20/RXR-27 using Symphony Link mode or NoMac mode. In Symphony Link mode, the module is configured to participate in a Symphony Link network, and communicates using the automatic functionality of the Symphony Link media-access control (MAC) protocol. In contrast, NoMac mode offers direct access to the module's low-level radio parameters.

Getting Started

Install Prelude

Download the latest version of the Prelude Windows Installer.

Launch the installer executable and click Next on the welcome screen.

Choose an installation location and click Install to start the installation.

Click Next to finish the installation of Prelude.

The installer prompts you to install drivers for the evaluation board's USB-to-UART bridge. These drivers allow your PC to recognize the evaluation board as a USB device. If you haven't already installed the drivers, click Yes and follow the on-screen instructions to install them.

Complete the Prelude installation by clicking Finish on the Prelude setup window.

Hardware Setup

This article walks you through hardware setup of an LL-RLP-20/RXR-27 evaluation board.

Attach the 915-MHz antenna to the evaluation board's SMA jack.

If you have not yet done so, install Prelude. Be sure to install the drivers for the evaluation board's USB-to-UART bridge when prompted.

Connect the evaluation board to a PC using a mini-USB cable. A new virtual serial port called Silicon Labs CP210x USB to UART Bridge will enumerate to the Ports (COM & LPT) section of the Windows Device Manager.

Once connected to the PC, the evaluation board's IO0 light-emitting diode illuminates, indicating the module has been RESET.

NoMac Mode

NoMac mode bypasses the Symphony Link MAC protocol and gives users the ability to evaluate the performance of the LoRa modulation format and the Semtech LoRa radio used by the LL-RLP-20 and LL-RXR-27. After shifting to NoMac mode from Symphony Link mode, the NO_MAC Prelude form opens.

Radio parameters

Set the desired radio parameters by checking the appropriate radio button from Prelude's Mode panel. The radio parameters of each selection are defined below.

Transmit power

In NoMac mode, the transmit power is always set to the highest power available from the module.

Time on Air

The LoRa physical layer allows many combinations of low-level parameters like the spreading factor (SF), bandwidth and coding rate (CR). These parameters affect the data rate, sensitivity, and time on air. In NoMac mode, Prelude limits selection or radio parameters to the three options listed in the table below. Each selection represents a trade-off between data rate and link margin.

Radio parameter set


Bandwidth (kHz)


low rate / max distance




mid rate / mid distance




max rate / short distance





Prelude allows several operating frequency bands: 868.5 - 868.6 MHz; 868.7 - 869.2 MHz; 869.4 - 869.65 MHz; 869.7 - 870 MHz; and 902 - 928 MHz. The entire LoRa transmission must fit within any one of the listed frequency bands.

Clicking the Set Frequency button sets the center frequency of the LoRa transmission.  If the selected radio parameters are incompatible with the selected frequency, Prelude will issue a warning similar to the following:


To open the Transmit Window, click the Show Transmit button.

The Transmit Window appears. To transmit a message, enter the text payload in the Message edit box and click the Transmit button.

The evaluation board's module will transmit the message using the selected radio parameters. After the transmission is complete, the module sets the IRQ_FLAGS_TX_DONE flag. Prelude automatically clears all IRQ flags each time the Transmit button is clicked so that new IRQ events may be observed.


Prelude will repeatedly transmit the same message if the Repeat check box is selected. Prelude will send the message, wait one second, and then attempt to transmit again. If the module is still transmitting the previous message, Prelude will wait another second and then attempt to transmit again. This process repeats until either the Stop button is clicked or the Repeat check box is de-selected.


Click the Start Receiving button to begin receiving messages sent from other NoMac-mode modules. Prelude will write the selected radio parameters to the module before it sets the module to receive. Upon receipt of a message, the module sets the IRQ_FLAGS_RX_DONE flag. Prelude then retrieves the message from the module and displays the message in the Receive Window.

The module is able to receive any LoRa transmissions with matching radio parameters.

Echo mode

A module using NoMac provides a special operating mode called Echo mode. In Echo mode assigns a module to be either a master or slave node. The master node initiates an echo transaction by transmitting a LoRa message. The slave node receives the transmission from the master and then promptly echos by transmitting the same message. The master node then attempts to receive the echo from the slave node.

To use Echo mode, attach an evaluation board to Prelude and select Options > Set Remote Echo Mode. This configures the attached module to be a slave node.

After the slave node is configured, detach it from Prelude and then attach the intended master node. Ensure the master node is using the same radio parameters as the slave node and then open the Transmit window and select the Echo Master check box.

Enter the desired message in the Message edit box and click Transmit.

Select the RF path

Setting the RF path is done in the same way for NoMac and Symphony Link modes.

Switching to Symphony Link mode

To switch Prelude to control the module using Symphony Link mode, select Options > Symphony Link. The NO_MAC Prelude form will close and a new Symphony Prelude form will open.


While in NoMac mode, Prelude's logging functionality is identical to that in Symphony Link mode.

IRQ Flags

The LL-RLP-20 and LL-RXR-27 are designed to be controlled by an external host microcontroler. The module-firmware provides a host interface, over which the host initiates communication with the module. If, on the other hand, the module needs to initiate communication with the host, it does so by raising IRQ (interrupt request) flags. The host detects IRQ flags by polling the module, and can then take appropriate action to respond.

Prelude provides a real-time graphical representation of which IRQ flags have been set by the evaluation board's module. This is useful to observe and understand the behavior of the module's firmware.

NoMac mode uses only a subset of the IRQ flags available to Symphony Link mode. The following table lists all IRQ flags and whether they are used by Symphony Link and/or NoMac mode. Please refer to documentation of the modules for further information regarding IRQ flags.

IRQ Flag

Symphony Link



































Firmware Updates with Prelude

Prelude offers an easy method to update the firmware of an evaluation board's module. Additionally, the latest release of Prelude is packaged with the latest release of module firmware, and Prelude will automatically prompt you to update the firmware of an out-of-date module when it is attached. Prelude uses the module's installed bootloader to load an encrypted binary image of the firmware update.

To load new firmware to the evaluation board's module, attach the module to Prelude and select Help > Load Firmware. The Load Firmware window will open.

Navigate to the path of the target encrypted binary and select the correct file. Then click Load Firmware.

The Load Firmware window indicates progress as the new firmware is flashed to the module.

When the firmware update is complete, the Load Firmware window indicates success. You can close the window.

Minimum firmware version

Prelude requires a minimum module firmware version to operate properly. If the attached module reports a firmware version older than the required minimum version, Prelude displays the following notification when the module is attached to Prelude.

Click Yes, and Prelude will automatically load the latest firmware release to the module.