OpenLCB Programmer's Guide

Code Configuration

Now we’ll create the actual OpenLCB node that produces alternating events. This demonstrates the core OpenLCB protocol behavior you learned in Chapter 1 (node initialization and event production) without requiring physical hardware.

Creating the Configuration Header

OpenMRNLite requires a configuration structure (CDI - Configuration Description Information) even for simple nodes. We’ll create a minimal config.h file.

Create the file include/config.h with this content:

#ifndef _ASYNC_BLINK_CONFIG_H_
#define _ASYNC_BLINK_CONFIG_H_

#include "openlcb/ConfigRepresentation.hxx"
#include "openlcb/MemoryConfig.hxx"

namespace openlcb {

/// SNIP Static Data - Manufacturer information (read-only, compiled into firmware)
extern const SimpleNodeStaticValues SNIP_STATIC_DATA = {
    4,               // Version
    "OpenMRN",       // Manufacturer
    "async_blink",   // Model
    "ESP32",         // Hardware version
    "1.00"           // Software version
};

/// SNIP Dynamic Data - User-editable node name and description
/// These are stored in the config file and can be read/written via JMRI
static const char SNIP_NODE_NAME[] = "async_blink";
static const char SNIP_NODE_DESC[] = "ESP32 Blink demo";

/// Version number for the configuration structure
static constexpr uint16_t CANONICAL_VERSION = 0x0001;

/// Minimal configuration segment with just internal config
CDI_GROUP(AsyncBlinkSegment, Segment(MemoryConfigDefs::SPACE_CONFIG), Offset(128));
CDI_GROUP_ENTRY(internal_config, InternalConfigData);
CDI_GROUP_END();

/// The main CDI structure
CDI_GROUP(ConfigDef, MainCdi());
CDI_GROUP_ENTRY(ident, Identification);
CDI_GROUP_ENTRY(acdi, Acdi);
CDI_GROUP_ENTRY(userinfo, UserInfoSegment, Name("User Info"));
CDI_GROUP_ENTRY(seg, AsyncBlinkSegment, Name("Settings"));
CDI_GROUP_END();

} // namespace openlcb

#endif // _ASYNC_BLINK_CONFIG_H_

What this does: Defines the CDI (Configuration Description Information) structure that OpenMRNLite uses to expose node configuration to JMRI. The configuration includes:

• SNIP Static Data: Read-only manufacturer, model, and version information (compiled into firmware)
• SNIP Dynamic Data: User-editable node name and description stored in the config file (visible in JMRI node properties)
• Acdi and UserInfo: Standard OpenLCB configuration segments
• AsyncBlinkSegment: Internal configuration area for this node (currently minimal, but available for future expansion)

Configuration Storage: Configuration is saved to SPIFFS on first boot (via factory_reset() shown in the next section) and persists across restarts. In v0.1, the initial configuration is hardcoded in the constants above. See the next chapter “Configuration & Persistence” (Chapter 4) to understand how configuration storage works, how to edit settings via JMRI, and how apply_configuration() fits into the lifecycle.