[debug](trx-backend-soapysdr): trace SDR retune application

Co-authored-by: OpenAI Codex <codex@openai.com>
Signed-off-by: Stan Grams <sjg@haxx.space>

src/trx-server/trx-backend/trx-backend-soapysdr/src/dsp.rs

@@ -288,15 +288,39 @@ fn iq_read_loop(
     let mut zero_read_streak: u32 = 0;
     let mut overflow_log_window_start: Option<Instant> = None;
     let mut overflow_log_suppressed: u32 = 0;
+    let mut retune_seq: u64 = 0;
+    let mut last_applied_retune_hz: Option<f64> = None;
 
     loop {
         // Apply any pending hardware retune before the next read.
         if let Ok(mut cmd) = retune_cmd.try_lock() {
             if let Some(hz) = cmd.take() {
+                retune_seq = retune_seq.wrapping_add(1);
+                let started = Instant::now();
+                tracing::warn!(
+                    "SDR retune request #{} starting: target={:.0} Hz, last_applied={}",
+                    retune_seq,
+                    hz,
+                    last_applied_retune_hz
+                        .map(|value| format!("{value:.0} Hz"))
+                        .unwrap_or_else(|| "none".to_string())
+                );
                 if let Err(e) = source.set_center_freq(hz) {
-                    tracing::warn!("SDR retune to {:.0} Hz failed: {}", hz, e);
+                    tracing::warn!(
+                        "SDR retune request #{} failed after {:?}: target={:.0} Hz: {}",
+                        retune_seq,
+                        started.elapsed(),
+                        hz,
+                        e
+                    );
                 } else {
-                    tracing::info!("SDR retuned to {:.0} Hz", hz);
+                    last_applied_retune_hz = Some(hz);
+                    tracing::info!(
+                        "SDR retune request #{} applied in {:?}: {:.0} Hz",
+                        retune_seq,
+                        started.elapsed(),
+                        hz
+                    );
                 }
             }
         }