From e6d22bce14469d6e4ffc2335c34282718e9ea1b0 Mon Sep 17 00:00:00 2001
From: Michael Pham <61564344+Mikefly123@users.noreply.github.com>
Date: Thu, 23 Jul 2026 23:34:54 -0700
Subject: [PATCH] perf(comdelay): pass comStatus straight through when DIVIDER
 == 0

Problem: file downlink over the USP LoRa radio is throughput-capped by
ComDelay. comStatusIn_handler only latched the radio's comStatus, and
run_handler (10 Hz via rateGroup10Hz -> downlinkDelay.run) released at
most one status per tick even with DIVIDER=0, quantizing the whole
downlink to ~10 frames/s (~2 kB/s at 248 B frames) regardless of air
rate.

Mechanism/fix: when DIVIDER == 0, comStatusIn_handler now forwards the
status to comStatusOut immediately instead of latching it, so ComQueue
is paced purely by radio TX-done. DIVIDER > 0 keeps the existing
latched/tick-paced behavior unchanged. Coherence: in passthrough mode
the valid flag is never set, so a status can't also be emitted by
run_handler (no duplication); a status latched under DIVIDER > 0 before
a runtime switch to 0 is still consumed by run_handler's
compare_exchange (no loss). ComDelay is passive, so the forward runs on
the radio-side caller thread; that is safe because comStatusOut feeds
ComQueue's async input (enqueue only). A grep-able image-currency
marker string is included.

HWIL A/B on the v5e + GRC-USP bench (P4_GFSK_75K both ends, radio-only
downlink path, 178,704 B FileDownlink SendFile, SendStarted->FileSent):
- baseline (latched, DIVIDER=0): 90.19 s = 1981 B/s (matches the ~105 s
  / 200 kB manual measurement)
- passthrough: 69.75 s = 2562 B/s and 71.47 s = 2500 B/s  (~1.28x)
- received files byte-identical to baseline (same cksum); no
  QueueOverflow storms, no panics/wedges; DIVIDER=9 still tick-paces
  (~0.8 frame/s observed); profile sweep + NO_OP commanding unaffected.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
---
 .../Components/ComDelay/ComDelay.cpp          | 33 +++++++++++++++++--
 1 file changed, 31 insertions(+), 2 deletions(-)

diff --git a/PROVESFlightControllerReference/Components/ComDelay/ComDelay.cpp b/PROVESFlightControllerReference/Components/ComDelay/ComDelay.cpp
index 687aac929..30244cb3f 100644
--- a/PROVESFlightControllerReference/Components/ComDelay/ComDelay.cpp
+++ b/PROVESFlightControllerReference/Components/ComDelay/ComDelay.cpp
@@ -38,9 +38,38 @@ void ComDelay ::parameterUpdated(FwPrmIdType id) {
 // Handler implementations for typed input ports
 // ----------------------------------------------------------------------
 
+// Image-currency marker: grep-able via `strings zephyr.elf` to verify the flashed
+// binary actually contains the divider-0 passthrough change (never trust "Verified OK").
+static volatile const char COMDELAY_DIV0_PASSTHROUGH_MARKER[] = "comdelay-div0-passthrough-20260723";
+
 void ComDelay ::comStatusIn_handler(FwIndexType portNum, Fw::Success& condition) {
-    this->m_last_status = condition;
-    this->m_last_status_valid = true;
+    // Read the divider; on invalid/uninit fall back to the default (matches run_handler).
+    Fw::ParamValid is_valid;
+    U16 current_divisor = this->paramGet_DIVIDER(is_valid);
+    if ((is_valid == Fw::ParamValid::INVALID) || (is_valid == Fw::ParamValid::UNINIT)) {
+        current_divisor = Components::DEFAULT_DIVIDER;
+    }
+
+    if (current_divisor == 0) {
+        // DIVIDER == 0 means "no delay": forward the status immediately instead of
+        // latching it for the next rate tick. This removes the rate-group quantization
+        // (one status per tick) so downlink is paced purely by radio TX-done.
+        //
+        // Threading note: ComDelay is passive, so this executes on the CALLER's thread
+        // (the radio-side comStatus source). That is safe because comStatusOut feeds an
+        // async input (ComQueue), which only enqueues a message here.
+        //
+        // Coherence with run_handler: in passthrough mode we never set
+        // m_last_status_valid, so this status cannot ALSO be emitted by run_handler
+        // (no duplication). A status latched earlier under DIVIDER > 0 is still
+        // consumed by run_handler's compare_exchange as before (no loss) if the
+        // divider is changed to 0 at runtime.
+        static_cast<void>(COMDELAY_DIV0_PASSTHROUGH_MARKER[0]);  // volatile read keeps the marker in the image
+        this->comStatusOut_out(0, condition);
+    } else {
+        this->m_last_status = condition;
+        this->m_last_status_valid = true;
+    }
 }
 
 void ComDelay ::run_handler(FwIndexType portNum, U32 context) {