Feature: Add support for recording from aux channels

Author: gilbert-sci

api/datatype.proto

@@ -66,6 +66,27 @@ message BroadbandFrame {
 
   // Used for reconstructing multiple frames
   uint32 sample_rate_hz = 4;
+
+  // Describes contiguous ranges of channel types in frame_data, in order.
+  // When empty, all frame_data entries are electrode channels (legacy behavior).
+  // Example: 
+  // [{type: ELECTRODE}, count: 64, {type:TTL, count:3, channel_ids:[0, 2, 5]}]
+  // This means frame_data[0..63] are electrodes, frame_data[64..66] are TTL lines 0, 2, 5
+  message ChannelRange {
+    enum ChannelType {
+      ELECTRODE = 0;
+      TTL = 1;
+    }
+    ChannelType type = 1;
+
+    // Number of channels of this type in frame_data
+    uint32 count = 2;
+
+    // Optional: for non-contiguous channels (e.g., TTL), specifies which
+    //           channel ids are included, in order. Empty for contiguous
+    repeated uint32 channel_ids = 3;
+  }
+  repeated ChannelRange channel_ranges = 5;
 }
 
 message Timeseries {

api/nodes/signal_config.proto

@@ -5,9 +5,29 @@ import "api/channel.proto";
 package synapse;
 
 message ElectrodeConfig {
+    // Electrode recording channels
     repeated Channel channels = 1;
+
+    // Analog filter settings for electrode channels
     float low_cutoff_hz = 2;
     float high_cutoff_hz = 3;
+
+    // Additional data channels to record beyond electrodes
+    // These will appear in the broadband data stream after electrode
+    // channels in the order specified here
+    message AuxiliaryChannel {
+        enum ChannelType {
+            TTL = 0;  // Digital input line
+        }
+        ChannelType type = 1;
+
+        // Channel identifier (TTL line 0-31, etc.)
+        uint32 channel_id = 2;
+
+        // Optional human-readable label
+        string label = 3;
+    }
+    repeated AuxiliaryChannel auxiliary_channels = 4;
 }
 
 message PixelConfig {