[feat](trx-rs): add FT2 decoder protocol support

Implement a distinct FT2 protocol path in the decoder stack and align\nits timing with the confirmed FT2 framing used by Decodium.\n\nCo-authored-by: OpenAI Codex <codex@openai.com>

Signed-off-by: Stanislaw Grams <stanislawgrams@gmail.com>

src/decoders/trx-ft8/build.rs

@@ -31,12 +31,21 @@ fn main() {
 
     println!("cargo:rerun-if-changed=src/ft8_wrapper.c");
     println!("cargo:rerun-if-changed={base}/common/monitor.c");
+    println!("cargo:rerun-if-changed={base}/common/monitor.h");
     println!("cargo:rerun-if-changed={base}/fft/kiss_fft.c");
+    println!("cargo:rerun-if-changed={base}/fft/kiss_fft.h");
     println!("cargo:rerun-if-changed={base}/fft/kiss_fftr.c");
+    println!("cargo:rerun-if-changed={base}/fft/kiss_fftr.h");
     println!("cargo:rerun-if-changed={base}/ft8/constants.c");
+    println!("cargo:rerun-if-changed={base}/ft8/constants.h");
     println!("cargo:rerun-if-changed={base}/ft8/crc.c");
+    println!("cargo:rerun-if-changed={base}/ft8/crc.h");
     println!("cargo:rerun-if-changed={base}/ft8/decode.c");
+    println!("cargo:rerun-if-changed={base}/ft8/decode.h");
     println!("cargo:rerun-if-changed={base}/ft8/ldpc.c");
+    println!("cargo:rerun-if-changed={base}/ft8/ldpc.h");
     println!("cargo:rerun-if-changed={base}/ft8/message.c");
+    println!("cargo:rerun-if-changed={base}/ft8/message.h");
     println!("cargo:rerun-if-changed={base}/ft8/text.c");
+    println!("cargo:rerun-if-changed={base}/ft8/text.h");
 }

src/decoders/trx-ft8/src/ft8_wrapper.c

@@ -11,6 +11,13 @@
 #include <string.h>
 #include <stdio.h>
 
+enum
+{
+    TRX_FTX_PROTOCOL_FT4 = 0,
+    TRX_FTX_PROTOCOL_FT8 = 1,
+    TRX_FTX_PROTOCOL_FT2 = 2,
+};
+
 // Callsign hash table (from demo/decode_ft8.c)
 #define CALLSIGN_HASHTABLE_SIZE 256
 
@@ -120,7 +127,19 @@ ft8_decoder_t* ft8_decoder_create(int sample_rate, float f_min, float f_max, int
     dec->cfg.sample_rate = sample_rate;
     dec->cfg.time_osr = time_osr;
     dec->cfg.freq_osr = freq_osr;
-    dec->cfg.protocol = (protocol == 0) ? FTX_PROTOCOL_FT4 : FTX_PROTOCOL_FT8;
+    switch (protocol)
+    {
+    case TRX_FTX_PROTOCOL_FT4:
+        dec->cfg.protocol = FTX_PROTOCOL_FT4;
+        break;
+    case TRX_FTX_PROTOCOL_FT2:
+        dec->cfg.protocol = FTX_PROTOCOL_FT2;
+        break;
+    case TRX_FTX_PROTOCOL_FT8:
+    default:
+        dec->cfg.protocol = FTX_PROTOCOL_FT8;
+        break;
+    }
 
     hashtable_init();
     monitor_init(&dec->mon, &dec->cfg);

src/decoders/trx-ft8/src/lib.rs

@@ -12,6 +12,9 @@ const TIME_OSR: i32 = 2;
 const FREQ_OSR: i32 = 2;
 
 const FTX_MAX_MESSAGE_LENGTH: usize = 35;
+const PROTOCOL_FT4: c_int = 0;
+const PROTOCOL_FT8: c_int = 1;
+const PROTOCOL_FT2: c_int = 2;
 
 #[repr(C)]
 #[derive(Clone, Copy)]
@@ -63,30 +66,18 @@ unsafe impl Send for Ft8Decoder {}
 
 impl Ft8Decoder {
     pub fn new(sample_rate: u32) -> Result<Self, String> {
-        unsafe {
-            let ptr = ft8_decoder_create(
-                sample_rate as c_int,
-                F_MIN_HZ,
-                F_MAX_HZ,
-                TIME_OSR as c_int,
-                FREQ_OSR as c_int,
-                1, // FTX_PROTOCOL_FT8
-            );
-            let inner = NonNull::new(ptr).ok_or_else(|| "ft8_decoder_create failed".to_string())?;
-            let block_size = ft8_decoder_block_size(inner.as_ptr()) as usize;
-            if block_size == 0 {
-                ft8_decoder_free(inner.as_ptr());
-                return Err("invalid FT8 block size".to_string());
-            }
-            Ok(Self {
-                inner,
-                block_size,
-                sample_rate,
-            })
-        }
+        Self::new_with_protocol(sample_rate, PROTOCOL_FT8, "FT8")
     }
 
     pub fn new_ft4(sample_rate: u32) -> Result<Self, String> {
+        Self::new_with_protocol(sample_rate, PROTOCOL_FT4, "FT4")
+    }
+
+    pub fn new_ft2(sample_rate: u32) -> Result<Self, String> {
+        Self::new_with_protocol(sample_rate, PROTOCOL_FT2, "FT2")
+    }
+
+    fn new_with_protocol(sample_rate: u32, protocol: c_int, label: &str) -> Result<Self, String> {
         unsafe {
             let ptr = ft8_decoder_create(
                 sample_rate as c_int,
@@ -94,13 +85,13 @@ impl Ft8Decoder {
                 F_MAX_HZ,
                 TIME_OSR as c_int,
                 FREQ_OSR as c_int,
-                0, // FTX_PROTOCOL_FT4
+                protocol,
             );
             let inner = NonNull::new(ptr).ok_or_else(|| "ft8_decoder_create failed".to_string())?;
             let block_size = ft8_decoder_block_size(inner.as_ptr()) as usize;
             if block_size == 0 {
                 ft8_decoder_free(inner.as_ptr());
-                return Err("invalid FT4 block size".to_string());
+                return Err(format!("invalid {label} block size"));
             }
             Ok(Self {
                 inner,
@@ -110,11 +101,6 @@ impl Ft8Decoder {
         }
     }
 
-    pub fn new_ft2(sample_rate: u32) -> Result<Self, String> {
-        // Wired to FT4 protocol pending a dedicated FT2 implementation.
-        Self::new_ft4(sample_rate)
-    }
-
     pub fn block_size(&self) -> usize {
         self.block_size
     }
@@ -179,3 +165,18 @@ impl Drop for Ft8Decoder {
         }
     }
 }
+
+#[cfg(test)]
+mod tests {
+    use super::Ft8Decoder;
+
+    #[test]
+    fn ft2_uses_distinct_block_size() {
+        let ft4 = Ft8Decoder::new_ft4(12_000).expect("ft4 decoder");
+        let ft2 = Ft8Decoder::new_ft2(12_000).expect("ft2 decoder");
+
+        assert!(ft2.block_size() < ft4.block_size());
+        assert_eq!(ft4.block_size(), 576);
+        assert_eq!(ft2.block_size(), 288);
+    }
+}