Check the tower is running its own settings, not the firmware's fallback

docs/test-command.md

@@ -54,7 +54,7 @@ While a test runs, interfering commands (moves, homing, a second test, capture,
 | `host` | `memory` | available RAM / swap (`/proc/meminfo`) |
 | `host` | `load` | load average vs CPU count |
 | `hardware` | `axes` | the axes `[Hardware] axes` declares appear in telemetry, **and no others** |
-| `hardware` | `motor` | `DUMP` echoes **everything** `hardware.ini` declares — current, `steps_per_rev`, `enc_deviation`, `sw_mode` and all three speeds — catching a stale flash, a lost `SET`, or an axis that never left `NEEDCFG` |
+| `hardware` | `motor` | `DUMP` echoes **everything** `hardware.ini` declares — current, `steps_per_rev`, `enc_deviation`, `sw_mode` and all three speeds — catching a stale flash, a lost `SET`, or an axis that never left `NEEDCFG`. Also checks the axis is not on the firmware's **limp-home** fallback, which `USE DEFAULTS` leaves looking fully configured |
 | `hardware` | `imu` | a declared IMU is connected and a sample arrives |
 | `hardware` | `env` | a declared ambient sensor sits on a **real I2C** adapter (not SMBus-only) and returns a CRC-valid reading |
 | `hardware` | `camera` | every configured camera opened; `usbfs_memory_mb` and USB3 LPM hold |
@@ -99,12 +99,21 @@ Three rules hold across every leaf:
   look identical from the sensor's side, and the distinction is what
   known-issues #2 cost to learn.
 
-The `motor` leaf reports two metrics per axis. `<axis>_current` covers
-`GLOBALSCALER`/`IRUN`/`homing IRUN`; `<axis>_declared` covers everything else the
-host owns. Both treat an **absent** field as unconfirmable rather than as a
-mismatch — comparing against a missing value would report "firmware has -1", which
-reads as a wrong setting and sends someone to re-send a command that was never the
-problem.
+The `motor` leaf reports three metrics per axis. `<axis>_not_limp` asks where the
+values came from; `<axis>_current` covers `GLOBALSCALER`/`IRUN`/`homing IRUN`; and
+`<axis>_declared` covers everything else the host owns. All three treat an
+**absent** field as unconfirmable rather than as a mismatch — comparing against a
+missing value would report "firmware has -1", which reads as a wrong setting and
+sends someone to re-send a command that was never the problem.
+
+`<axis>_not_limp` runs first because it explains the other two. `USE DEFAULTS` is
+the deliberate bench escape from `NEEDCFG`, and it fills the firmware's `cfg_rx`
+mask completely — so an axis running limp-home values leaves `NEEDCFG`, reports
+`READY`, and passes every state check while running numbers that describe no real
+drivetrain. Without this metric the only symptom is `<axis>_declared` listing six
+mismatches, which reads as "host and firmware disagree" and sends someone to
+re-send values that were never sent at all. The fix is a host restart, which
+re-sends the whole declared block.
 
 The `motor` leaf is the one worth running after every flash: `GLOBALSCALER` and
 `IRUN` are **write-only** on the TMC5160, so the `DUMP` echo is the only evidence

include/fgc/DumpParser.h

@@ -42,6 +42,11 @@ struct DumpAxis {
     // Bitmask over the firmware's CfgKey: which required keys have arrived.
     // -1 when absent.
     long        cfg_received  = -1;
+    // Is the axis running the firmware's limp-home fallback rather than anything
+    // this host declared? USE DEFAULTS fills cfg_received with the whole required
+    // mask, so that field alone cannot tell the two apart - a bench board reads as
+    // fully configured. -1 when absent, i.e. a firmware predating the flag.
+    long        limp_home     = -1;
     // Encoder-tracking health accumulated by the firmware hold corrector.
     long        hold_corrections = 0;     // # of hold resyncs since firmware boot/RESET
     long        hold_peak_dev = 0;        // largest deviation seen while holding (counts)

include/fgc/HardwareChecks.h

@@ -88,6 +88,23 @@ struct DrivetrainEcho {
 CheckResult checkDrivetrainAdopted(const std::string& axis, const DrivetrainExpectation& want,
                                    const DrivetrainEcho& got);
 
+// Is the axis running the host's configuration, or the firmware's limp-home
+// fallback?
+//
+// `USE DEFAULTS` is the deliberate bench escape from NEEDCFG, and it fills the
+// firmware's cfg_rx mask completely - so an axis on limp-home values reports as
+// fully configured and passes every state check. What gives it away is the DUMP
+// `limp` flag, which says where the values came from rather than whether they
+// arrived.
+//
+// checkDeclaredValues() would also catch this, but only as a list of mismatched
+// numbers, which reads as "the host and firmware disagree" and sends someone to
+// re-send them. The truthful diagnosis is that nobody ever sent any.
+//
+// `limp` < 0 means the firmware predates the flag: reported as not-run, because
+// an old firmware is a version skew rather than a misconfigured tower.
+CheckResult checkNotLimpHome(const std::string& axis, long limp);
+
 // Does the homed travel fit entirely in positive counts?
 //
 // `center_count` defines where the middle of the found travel sits, so the range

src/core/DumpParser.cpp

@@ -176,6 +176,7 @@ DumpData parseDump(const std::string& block) {
             ax.center_speed    = asInt(get(m, "center_speed", "-1"));
             ax.sw_mode         = asInt(get(m, "sw_mode", "-1"));
             ax.cfg_received    = asInt(get(m, "cfg_rx", "-1"), -1);
+            ax.limp_home       = asInt(get(m, "limp", "-1"), -1);
             ax.hold_corrections    = asInt(get(m, "hold_corr", "0"));
             ax.hold_peak_dev       = asInt(get(m, "hold_peak", "0"));
             ax.hold_cumulative_dev = asInt(get(m, "hold_cumul", "0"));
@@ -222,6 +223,10 @@ std::vector<std::string> formatDump(const DumpData& d) {
                << "  limits=[" << ax.lim_neg << ".." << ax.lim_pos << "]"
                << "  hold_target=" << ax.hold_target
                << "  has_encoder=" << (ax.has_encoder ? 1 : 0);
+            // Shown only when set. It is a fault on a tower - the axis is on the
+            // firmware's fallback values, not hardware.ini's - and printing
+            // "limp=0" on every healthy dump would bury it.
+            if (ax.limp_home > 0) os << "  LIMP-HOME (not hardware.ini's values)";
             out.push_back(os.str());
         }
         for (const char* k : {"GCONF", "CHOPCONF", "XACTUAL", "X_ENC", "XTARGET", "VACTUAL"}) {

src/core/HardwareChecks.cpp

@@ -79,6 +79,28 @@ CheckResult checkI2cFunctionality(unsigned long funcs) {
     return r;
 }
 
+CheckResult checkNotLimpHome(const std::string& axis, long limp) {
+    CheckResult r;
+
+    if (limp < 0) {
+        r.ran    = false;
+        r.detail = axis +
+                   ": firmware does not report the limp flag, so whether it is running "
+                   "hardware.ini's values or its own fallback cannot be told apart here";
+        return r;
+    }
+
+    r.pass = (limp == 0);
+    r.detail = r.pass
+                   ? axis + ": running the host's declared values"
+                   : axis +
+                         ": running LIMP-HOME values, which describe no real drivetrain -- slow "
+                         "speeds, a reduced search current and a placeholder travel. Something "
+                         "sent USE DEFAULTS, so hardware.ini is NOT in force however healthy the "
+                         "axis looks. Restart the host to re-send it";
+    return r;
+}
+
 CheckResult checkDrivetrainAdopted(const std::string& axis, const DrivetrainExpectation& want,
                                    const DrivetrainEcho& got) {
     CheckResult r;

src/core/TestRunner.cpp

@@ -828,6 +828,7 @@ long echoSwMode(const DumpData& d, char c)       { return axisField(d, c, &DumpA
 long echoHomingSpeed(const DumpData& d, char c)  { return axisField(d, c, &DumpAxis::homing_speed); }
 long echoCenterSpeed(const DumpData& d, char c)  { return axisField(d, c, &DumpAxis::center_speed); }
 long echoSpeed(const DumpData& d, char c)        { return axisField(d, c, &DumpAxis::speed); }
+long echoLimp(const DumpData& d, char c)         { return axisField(d, c, &DumpAxis::limp_home); }
 
 // The VMAX a declared deg/s becomes on this axis, or 0 when it cannot be formed.
 // Mirrors Application's fallback: the live calibration when it is trustworthy,
@@ -925,6 +926,12 @@ void TestRunner::testHwMotor(TestReport& r) {
     }
 
     auto check_axis = [&](const char* name, char code, const AxisDrivetrainConfig& cfg) {
+        // First, because it explains the rest. An axis on limp-home values will
+        // fail every comparison below, and that list of mismatched numbers reads
+        // as "host and firmware disagree" - sending someone to re-send values
+        // that were never sent at all.
+        verdict(s, std::string(name) + "_not_limp", checkNotLimpHome(name, echoLimp(d, code)));
+
         DrivetrainExpectation want;
         if (cfg.run_current_ma > 0.0 && cfg.r_sense_ohm > 0.0) {
             const auto plan = planTmcCurrent(cfg.r_sense_ohm, cfg.run_current_ma,

tests/test_hardwarechecks.cpp

@@ -41,6 +41,35 @@ TEST_CASE("an SMBus-only adapter is caught before it looks like a dead sensor")
     CHECK(smbus.detail.find("i2cdetect -F") != std::string::npos);
 }
 
+TEST_CASE("a tower on limp-home values is a fault, however healthy it looks") {
+    // The case this exists for: USE DEFAULTS fills the firmware's cfg_rx mask
+    // completely, so the axis leaves NEEDCFG, reports READY and passes every
+    // state check - while running values that describe no real drivetrain.
+    auto r = checkNotLimpHome("yaw", 1);
+    CHECK(r.ran);
+    CHECK_FALSE(r.pass);
+    CHECK(r.detail.find("LIMP-HOME") != std::string::npos);
+    // It must send the reader to the cause, not to the symptom. "Re-send the
+    // values" is the wrong instruction when nobody ever sent any.
+    CHECK(r.detail.find("USE DEFAULTS") != std::string::npos);
+    CHECK(r.detail.find("Restart the host") != std::string::npos);
+}
+
+TEST_CASE("an axis on the host's own values passes") {
+    auto r = checkNotLimpHome("yaw", 0);
+    CHECK(r.ran);
+    CHECK(r.pass);
+}
+
+TEST_CASE("a firmware with no limp flag is a version skew, not a passing tower") {
+    // Absent must not read as limp=0. A firmware predating the flag genuinely
+    // cannot answer the question, and claiming PASS here would assert something
+    // the wire never said - the same -1-is-not-zero rule the current echo uses.
+    auto r = checkNotLimpHome("yaw", -1);
+    CHECK_FALSE(r.ran);
+    CHECK(r.detail.find("cannot be told apart") != std::string::npos);
+}
+
 TEST_CASE("an undeclared axis has no drivetrain skew to find") {
     DrivetrainExpectation want;  // declared == false
     DrivetrainEcho        got;   // all -1