From 688c6ee114d22ec60d8ea4693fbae0c8a131561c Mon Sep 17 00:00:00 2001
From: Simon Duquennoy <simon.duquennoy@gmail.com>
Date: Sat, 15 Jul 2017 12:08:10 +0200
Subject: [PATCH] TSCH: comment on how the TSCH base drift is computed

---
 arch/platform/cc2538dk/contiki-conf.h        |  9 ++++++++-
 arch/platform/jn516x/platform-conf.h         | 12 +++++++++---
 arch/platform/openmote-cc2538/contiki-conf.h |  9 ++++++++-
 arch/platform/srf06-cc26xx/contiki-conf.h    |  9 ++++++++-
 arch/platform/zoul/contiki-conf.h            |  9 ++++++++-
 5 files changed, 41 insertions(+), 7 deletions(-)

diff --git a/arch/platform/cc2538dk/contiki-conf.h b/arch/platform/cc2538dk/contiki-conf.h
index 307b015fe..a3ef81196 100644
--- a/arch/platform/cc2538dk/contiki-conf.h
+++ b/arch/platform/cc2538dk/contiki-conf.h
@@ -47,7 +47,14 @@ typedef uint32_t rtimer_clock_t;
 #define RADIO_DELAY_BEFORE_DETECT 0
 #ifndef TSCH_CONF_BASE_DRIFT_PPM
 /* The drift compared to "true" 10ms slots.
- * Enable adaptive sync to enable compensation for this. */
+ * Enable adaptive sync to enable compensation for this.
+ * Slot length 10000 usec
+ *             328 ticks
+ * Tick duration 30.517578125 usec
+ * Real slot duration 10009.765625 usec
+ * Target - real duration = -9.765625 usec
+ * TSCH_CONF_BASE_DRIFT_PPM -977
+ */
 #define TSCH_CONF_BASE_DRIFT_PPM -977
 #endif
 /*---------------------------------------------------------------------------*/
diff --git a/arch/platform/jn516x/platform-conf.h b/arch/platform/jn516x/platform-conf.h
index 703826ce7..3caadae2f 100644
--- a/arch/platform/jn516x/platform-conf.h
+++ b/arch/platform/jn516x/platform-conf.h
@@ -110,9 +110,15 @@ typedef uint32_t rtimer_clock_t;
 
 /* If the timer base a binary 32kHz clock, compensate for this base drift */
 #if RTIMER_USE_32KHZ && JN516X_EXTERNAL_CRYSTAL_OSCILLATOR
-/* Drift calculated using this formula:
-*    ((US_TO_TICKS(10000) * 100) - RTIMER_SECOND) * 1e6 = 976.5625 ppm
-*/
+/* The drift compared to "true" 10ms slots.
+ * Enable adaptive sync to enable compensation for this.
+ * Slot length 10000 usec
+ *             328 ticks
+ * Tick duration 30.517578125 usec
+ * Real slot duration 10009.765625 usec
+ * Target - real duration = -9.765625 usec
+ * TSCH_CONF_BASE_DRIFT_PPM -977
+ */
 #define TSCH_CONF_BASE_DRIFT_PPM -977
 #endif
 
diff --git a/arch/platform/openmote-cc2538/contiki-conf.h b/arch/platform/openmote-cc2538/contiki-conf.h
index d28a85ba3..5e7e967da 100644
--- a/arch/platform/openmote-cc2538/contiki-conf.h
+++ b/arch/platform/openmote-cc2538/contiki-conf.h
@@ -86,7 +86,14 @@ typedef uint32_t rtimer_clock_t;
 #define RADIO_DELAY_BEFORE_DETECT 0
 #ifndef TSCH_CONF_BASE_DRIFT_PPM
 /* The drift compared to "true" 10ms slots.
- * Enable adaptive sync to enable compensation for this. */
+ * Enable adaptive sync to enable compensation for this.
+ * Slot length 10000 usec
+ *             328 ticks
+ * Tick duration 30.517578125 usec
+ * Real slot duration 10009.765625 usec
+ * Target - real duration = -9.765625 usec
+ * TSCH_CONF_BASE_DRIFT_PPM -977
+ */
 #define TSCH_CONF_BASE_DRIFT_PPM -977
 #endif
 /*---------------------------------------------------------------------------*/
diff --git a/arch/platform/srf06-cc26xx/contiki-conf.h b/arch/platform/srf06-cc26xx/contiki-conf.h
index bb51131e9..4f464809a 100644
--- a/arch/platform/srf06-cc26xx/contiki-conf.h
+++ b/arch/platform/srf06-cc26xx/contiki-conf.h
@@ -280,7 +280,14 @@ typedef uint32_t rtimer_clock_t;
 
 #ifndef TSCH_CONF_BASE_DRIFT_PPM
 /* The drift compared to "true" 10ms slots.
- * Enable adaptive sync to enable compensation for this. */
+ * Enable adaptive sync to enable compensation for this.
+ * Slot length 10000 usec
+ *             328 ticks
+ * Tick duration 30.517578125 usec
+ * Real slot duration 10009.765625 usec
+ * Target - real duration = -9.765625 usec
+ * TSCH_CONF_BASE_DRIFT_PPM -977
+ */
 #define TSCH_CONF_BASE_DRIFT_PPM -977
 #endif
 
diff --git a/arch/platform/zoul/contiki-conf.h b/arch/platform/zoul/contiki-conf.h
index 38b34e5ad..a67e37e2c 100644
--- a/arch/platform/zoul/contiki-conf.h
+++ b/arch/platform/zoul/contiki-conf.h
@@ -84,7 +84,14 @@ typedef uint32_t rtimer_clock_t;
 #define RADIO_DELAY_BEFORE_DETECT 0
 #ifndef TSCH_CONF_BASE_DRIFT_PPM
 /* The drift compared to "true" 10ms slots.
- * Enable adaptive sync to enable compensation for this. */
+ * Enable adaptive sync to enable compensation for this.
+ * Slot length 10000 usec
+ *             328 ticks
+ * Tick duration 30.517578125 usec
+ * Real slot duration 10009.765625 usec
+ * Target - real duration = -9.765625 usec
+ * TSCH_CONF_BASE_DRIFT_PPM -977
+ */
 #define TSCH_CONF_BASE_DRIFT_PPM -977
 #endif
 /*---------------------------------------------------------------------------*/