Fix #442: make RX timing closer to Semtech's

Author: terrillmoore

examples/compliance-otaa-halconfig/compliance-otaa-halconfig.ino

@@ -310,8 +310,8 @@ void printAllRegisters(void) {
             printNl();
             printHex2(i);
         }
+        Serial.print(((i % 8) == 0) ? F(" - ") : F(" "));
         printHex2(regbuf[i]);
-        Serial.print(((i % 16) == 8) ? F(" - ") : F(" "));
     }
 
     // reset the radio, just in case the register dump caused issues.
@@ -630,7 +630,8 @@ void setup() {
     // Reset the MAC state. Session and pending data transfers will be discarded.
     LMIC_reset();
 
-    LMIC_setClockError(1 * MAX_CLOCK_ERROR / 100);
+    // set clock rate error to 0.1%
+    LMIC_setClockError(1 * MAX_CLOCK_ERROR / 1000);
 
     // do the network-specific setup prior to join.
     setupForNetwork(false);

src/lmic/lmic.c

@@ -306,11 +306,11 @@ static ostime_t calcRxWindow (u1_t secs, dr_t dr) {
         rxoff = (LMIC.drift * (ostime_t)secs) >> BCN_INTV_exp;
         err = (LMIC.lastDriftDiff * (ostime_t)secs) >> BCN_INTV_exp;
     }
-    u1_t rxsyms = MINRX_SYMS;
+    u1_t rxsyms = LMICbandplan_MINRX_SYMS_LoRa_ClassB;
     err += (ostime_t)LMIC.maxDriftDiff * LMIC.missedBcns;
-    LMIC.rxsyms = MINRX_SYMS + (err / dr2hsym(dr));
+    LMIC.rxsyms = LMICbandplan_MINRX_SYMS_LoRa_ClassB + (err / dr2hsym(dr));
 
-    return (rxsyms-PAMBL_SYMS) * dr2hsym(dr) + rxoff;
+    return (rxsyms-LMICbandplan_PAMBL_SYMS) * dr2hsym(dr) + rxoff;
 }
 
 
@@ -323,8 +323,8 @@ static void calcBcnRxWindowFromMillis (u1_t ms, bit_t ini) {
         LMIC.bcninfo.flags |= BCN_NODRIFT|BCN_NODDIFF;
     }
     ostime_t hsym = dr2hsym(DR_BCN);
-    LMIC.bcnRxsyms = MINRX_SYMS + ms2osticksCeil(ms) / hsym;
-    LMIC.bcnRxtime = LMIC.bcninfo.txtime + BCN_INTV_osticks - (LMIC.bcnRxsyms-PAMBL_SYMS) * hsym;
+    LMIC.bcnRxsyms = LMICbandplan_MINRX_SYMS_LoRa_ClassB + ms2osticksCeil(ms) / hsym;
+    LMIC.bcnRxtime = LMIC.bcninfo.txtime + BCN_INTV_osticks - (LMIC.bcnRxsyms-LMICbandplan_PAMBL_SYMS) * hsym;
 }
 #endif // !DISABLE_BEACONS
 
@@ -1421,14 +1421,7 @@ static void setupRx2 (void) {
     radioRx();
 }
 
-
-static void schedRx12 (ostime_t delay, osjobcb_t func, u1_t dr) {
-    ostime_t hsym = dr2hsym(dr);
-
-    LMIC.rxsyms = MINRX_SYMS;
-
-    // If a clock error is specified, compensate for it by extending the
-    // receive window
+ostime_t LMICcore_adjustForDrift (ostime_t delay, ostime_t hsym) {
     if (LMIC.client.clockError != 0) {
         // Calculate how much the clock will drift maximally after delay has
         // passed. This indicates the amount of time we can be early
@@ -1437,20 +1430,47 @@ static void schedRx12 (ostime_t delay, osjobcb_t func, u1_t dr) {
 
         // Increase the receive window by twice the maximum drift (to
         // compensate for a slow or a fast clock).
-        // decrease the rxtime to compensate for. Note that hsym is a
-        // *half* symbol time, so the factor 2 is hidden. First check if
-        // this would overflow (which can happen if the drift is very
-        // high, or the symbol time is low at high datarates).
-        if ((255 - LMIC.rxsyms) * hsym < drift)
+        delay -= drift;
+
+        // adjust rxsyms (the size of the window in syms) according to our
+        // uncertainty. do this in a strange order to avoid a divide if we can.
+        // rely on hsym = Tsym / 2
+        if ((255 - LMIC.rxsyms) * hsym < drift) {
             LMIC.rxsyms = 255;
-        else
-            LMIC.rxsyms += drift / hsym;
+        } else {
+            LMIC.rxsyms = (u1_t) (LMIC.rxsyms + drift / hsym);
+        }
+    }
+    return delay;
+}
+
+ostime_t LMICcore_RxWindowOffset (ostime_t hsym, u1_t rxsyms_in) {
+    ostime_t const Tsym = 2 * hsym;
+    ostime_t rxsyms;
+    ostime_t rxoffset;
 
+    rxsyms = ((2 * (int)rxsyms_in - 8) * Tsym + LMICbandplan_RX_ERROR_ABS_osticks * 2 + Tsym - 1) / Tsym;
+    if (rxsyms < rxsyms_in) {
+        rxsyms = rxsyms_in;
     }
+    LMIC.rxsyms = (u1_t) rxsyms;
+
+    rxoffset = (8 - rxsyms) * hsym - LMICbandplan_RX_EXTRA_MARGIN_osticks;
+
+    return rxoffset;
+}
 
-    // Center the receive window on the center of the expected preamble
+static void schedRx12 (ostime_t delay, osjobcb_t func, u1_t dr) {
+    ostime_t hsym = dr2hsym(dr);
+
+    // Center the receive window on the center of the expected preamble and timeout.
     // (again note that hsym is half a sumbol time, so no /2 needed)
-    LMIC.rxtime = LMIC.txend + delay + PAMBL_SYMS * hsym - LMIC.rxsyms * hsym;
+    // we leave RX_RAMPUP unadjusted for the clock drift.  The IBM LMIC generates delays
+    // that are too long for SF12, and too short for other SFs, so we follow the
+    // Semtech reference code.
+    //
+    // This also sets LMIC.rxsyms.
+    LMIC.rxtime = LMIC.txend + LMICcore_adjustForDrift(delay + LMICcore_RxWindowOffset(hsym, LMICbandplan_MINRX_SYMS_LoRa_ClassA), hsym);
 
     LMIC_X_DEBUG_PRINTF("%"LMIC_PRId_ostime_t": sched Rx12 %"LMIC_PRId_ostime_t"\n", os_getTime(), LMIC.rxtime - RX_RAMPUP);
     os_setTimedCallback(&LMIC.osjob, LMIC.rxtime - RX_RAMPUP, func);

src/lmic/lmic.h

@@ -103,9 +103,9 @@ extern "C"{
 
 // Arduino LMIC version
 #define ARDUINO_LMIC_VERSION_CALC(major, minor, patch, local)	\
-	(((major) << UINT32_C(24)) | ((minor) << UINT32_C(16)) | ((patch) << UINT32_C(8)) | ((local << UINT32_C(0))))
+	(((major) << 24ul) | ((minor) << 16ul) | ((patch) << 8ul) | ((local) << 0ul))
 
-#define	ARDUINO_LMIC_VERSION	ARDUINO_LMIC_VERSION_CALC(3, 0, 99, 1)	/* v3.0.99.1 */
+#define	ARDUINO_LMIC_VERSION	ARDUINO_LMIC_VERSION_CALC(3, 0, 99, 2)	/* v3.0.99.2 */
 
 #define	ARDUINO_LMIC_VERSION_GET_MAJOR(v)	\
 	(((v) >> 24u) & 0xFFu)

src/lmic/lmic_bandplan.h

@@ -169,13 +169,35 @@
 //
 // Things common to lmic.c code
 //
+#define	LMICbandplan_MINRX_SYMS_LoRa_ClassA	6
+#define	LMICbandplan_RX_ERROR_ABS_osticks	ms2osticks(10)
+
+// Semtech inherently (by calculating in ms and taking ceilings)
+// rounds up to the next higher ms. It's a lot easier for us
+// to just add margin for things like hardware ramp-up time
+// and clock calibration when running from the LSE and HSI
+// clocks on an STM32.
+#define LMICbandplan_RX_EXTRA_MARGIN_osticks	us2osticks(2000)
+
+// probably this should be the same as the Class-A value, but
+// we have not the means to thoroughly test this. This is the
+// number of rxsyms used in the computations for ping and beacon
+// windows.
+#define	LMICbandplan_MINRX_SYMS_LoRa_ClassB	5
+
+#define LMICbandplan_PAMBL_SYMS 8
+#define LMICbandplan_PAMBL_FSK  5
+#define LMICbandplan_PRERX_FSK  1
+#define LMICbandplan_RXLEN_FSK  (1+5+2)
+
+// Legacy names
 #if !defined(MINRX_SYMS)
-#define MINRX_SYMS 5
+# define MINRX_SYMS	LMICbandplan_MINRX_SYMS_LoRa_ClassB
 #endif // !defined(MINRX_SYMS)
-#define PAMBL_SYMS 8
-#define PAMBL_FSK  5
-#define PRERX_FSK  1
-#define RXLEN_FSK  (1+5+2)
+#define PAMBL_SYMS	LMICbandplan_PAMBL_SYMS
+#define PAMBL_FSK	LMICbandplan_PAMBL_FSK
+#define PRERX_FSK	LMICbandplan_PRERX_FSK
+#define	RXLEN_FSK	LMICbandplan_RXLEN_FSK
 
 // this is regional, but so far all regions are the same
 #if !defined(LMICbandplan_MAX_FCNT_GAP)
@@ -204,5 +226,7 @@
 // internal APIs
 ostime_t LMICcore_rndDelay(u1_t secSpan);
 void LMICcore_setDrJoin(u1_t reason, u1_t dr);
+ostime_t LMICcore_adjustForDrift(ostime_t delay, ostime_t hsym);
+ostime_t LMICcore_RxWindowOffset(ostime_t hsym, u1_t rxsyms_in);
 
 #endif // _lmic_bandplan_h_

src/lmic/lmic_eu_like.c

@@ -254,28 +254,13 @@ void LMICeulike_setRx1Freq(void) {
 // Class A txDone handling for FSK.
 void
 LMICeulike_txDoneFSK(ostime_t delay, osjobcb_t func) {
-        LMIC.rxsyms = RXLEN_FSK;
+        ostime_t const hsym = us2osticksRound(80);
 
-        // If a clock error is specified, compensate for it by extending the
-        // receive window
-        delay -= PRERX_FSK * us2osticksRound(160);
+        // start a little earlier.
+        delay -= LMICbandplan_PRERX_FSK * us2osticksRound(160);
 
-        if (LMIC.client.clockError != 0) {
-                // Calculate how much the clock will drift maximally after delay has
-                // passed. This indicates the amount of time we can be early
-                // _or_ late.
-                ostime_t drift = (int64_t)delay * LMIC.client.clockError / MAX_CLOCK_ERROR;
-
-                // Increase the receive window by twice the maximum drift (to
-                // compensate for a slow or a fast clock).
-                // decrease the rxtime to compensate for. Note that hsym is a
-                // *half* symbol time, so the factor 2 is hidden. First check if
-                // this would overflow (which can happen if the drift is very
-                // high, or the symbol time is low at high datarates).
-                delay -= drift;
-        }
-
-        LMIC.rxtime = LMIC.txend + delay;
+        // set LMIC.rxtime and LMIC.rxsyms:
+        LMIC.rxtime = LMIC.txend + LMICcore_adjustForDrift(delay + LMICcore_RxWindowOffset(hsym, LMICbandplan_RXLEN_FSK), hsym);
         os_setTimedCallback(&LMIC.osjob, LMIC.rxtime - RX_RAMPUP, func);
 }
 

src/lmic/oslmic.h

@@ -119,11 +119,19 @@ void radio_monitor_rssi(ostime_t n, oslmic_radio_rssi_t *pRssi);
 
 //================================================================================
 
-
 #ifndef RX_RAMPUP
+// RX_RAMPUP specifies the extra time we must allow to set up an RX event due
+// to platform issues. It's specified in units of ostime_t. It must reflect
+// platform jitter and latency, as well as the speed of the LMIC when running
+// on this plaform.
 #define RX_RAMPUP  (us2osticks(2000))
 #endif
+
 #ifndef TX_RAMPUP
+// TX_RAMPUP specifies the extra time we must allow to set up a TX event) due
+// to platform issues. It's specified in units of ostime_t. It must reflect
+// platform jitter and latency, as well as the speed of the LMIC when running
+// on this plaform.
 #define TX_RAMPUP  (us2osticks(2000))
 #endif