Fix drift of system_timer_current_time

inc/core/MicroBitConfig.h

@@ -189,6 +189,12 @@ extern uint32_t __etext;
 #define MICROBIT_IDLE_COMPONENTS                6
 #endif
 
+// Use MicroBitTick64 to fix slow running of system_timer_current_time
+// Default is zero because existing code may have workarounds that would be broken by this fix
+#ifndef MICROBIT_TICK64
+#define MICROBIT_TICK64 0
+#endif
+
 //
 // BLE options
 //

inc/core/MicroBitTick64.h

@@ -0,0 +1,81 @@
+/*
+The MIT License (MIT)
+
+Copyright (c) 2020 Insight Resources
+
+Permission is hereby granted, free of charge, to any person obtaining a
+copy of this software and associated documentation files (the "Software"),
+to deal in the Software without restriction, including without limitation
+the rights to use, copy, modify, merge, publish, distribute, sublicense,
+and/or sell copies of the Software, and to permit persons to whom the
+Software is furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in
+all copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
+THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
+DEALINGS IN THE SOFTWARE.
+*/
+
+#ifndef MICROBIT_TICK64_H
+#define MICROBIT_TICK64_H
+
+#include "mbed.h"
+#include "MicroBitConfig.h"
+
+
+typedef struct microbit_tick64_t
+{
+  uint32_t low0;  // microseconds
+  uint32_t high;  // microbit_tick64_highunit microseconds
+} microbit_tick64_t;
+
+
+extern microbit_tick64_t  microbit_tick640;
+extern microbit_tick64_t  microbit_tick641;
+extern microbit_tick64_t *microbit_tick64;
+extern const uint32_t     microbit_tick64_highunit;
+
+
+inline void microbit_tick64_initialise()
+{
+    microbit_tick64 = &microbit_tick640;
+    microbit_tick64->low0 = us_ticker_read();
+    microbit_tick64->high = 0;
+}
+
+
+/**
+ * Check the microsecond ticker and swap microbit_tick64_t instances
+ * Not reentrant. Call from one place. e.g. in a ticker.
+ * Assumes the microsecond ticker difference is less than
+ * 2 * microbit_tick64_highunit and calculates new values when
+ * the difference is between microbit_tick64_highunit and 0xFFFFFFF.
+ * With microbit_tick64_highunit = 0x80000000, the check is needed
+ * every 30mins and rollover is after 250,000 years
+*/
+inline void microbit_tick64_update()
+{
+    if ( us_ticker_read() - microbit_tick64->low0 > microbit_tick64_highunit)
+    {
+        microbit_tick64_t *other = microbit_tick64 == &microbit_tick640 ? &microbit_tick641 : &microbit_tick640;
+        other->low0 = microbit_tick64->low0 + microbit_tick64_highunit;
+        other->high = microbit_tick64->high + 1;
+        microbit_tick64 = other;
+    }
+}
+
+
+inline uint64_t microbit_tick64_microseconds()
+{
+    microbit_tick64_t *p = microbit_tick64; // guard against IRQ changing microbit_tick64
+    return microbit_tick64_highunit * ( uint64_t) p->high + ( us_ticker_read() - p->low0);
+}
+
+
+#endif

inc/platform/yotta_cfg_mappings.h

@@ -35,6 +35,10 @@
     #define MICROBIT_IDLE_COMPONENTS YOTTA_CFG_MICROBIT_DAL_IDLE_COMPONENTS
 #endif
 
+#ifdef YOTTA_CFG_MICROBIT_DAL_TICK64
+    #define MICROBIT_TICK64 YOTTA_CFG_MICROBIT_DAL_TICK64
+#endif
+
 #ifdef YOTTA_CFG_MICROBIT_DAL_BLUETOOTH_ENABLED
     #define MICROBIT_BLE_ENABLED YOTTA_CFG_MICROBIT_DAL_BLUETOOTH_ENABLED
 #endif

source/CMakeLists.txt

@@ -14,6 +14,7 @@ set(YOTTA_AUTO_MICROBIT-DAL_CPP_FILES
     "core/MicroBitHeapAllocator.cpp"
     "core/MicroBitListener.cpp"
     "core/MicroBitSystemTimer.cpp"
+    "core/MicroBitTick64.cpp"
     "core/MicroBitUtil.cpp"
 
     "types/CoordinateSystem.cpp"

source/core/MicroBitSystemTimer.cpp

@@ -38,11 +38,21 @@ DEALINGS IN THE SOFTWARE.
 #include "MicroBitSystemTimer.h"
 #include "ErrorNo.h"
 
+
+#if CONFIG_ENABLED( MICROBIT_TICK64)
+
+#include "MicroBitTick64.h"
+
+#else // CONFIG_ENABLED( MICROBIT_TICK64)
+
 /*
  * Time since power on. Measured in milliseconds.
  * When stored as an unsigned long, this gives us approx 50 days between rollover, which is ample. :-)
  */
 static uint64_t time_us = 0;
+
+#endif //CONFIG_ENABLED( MICROBIT_TICK64)
+
 static unsigned int tick_period = 0;
 
 // Array of components which are iterated during a system tick
@@ -51,9 +61,13 @@ static MicroBitComponent* systemTickComponents[MICROBIT_SYSTEM_COMPONENTS];
 // Periodic callback interrupt
 static Ticker *ticker = NULL;
 
+#if CONFIG_ENABLED( MICROBIT_TICK64)
+#else // CONFIG_ENABLED( MICROBIT_TICK64)
+
 // System timer.
 static Timer *timer = NULL;
 
+#endif //CONFIG_ENABLED( MICROBIT_TICK64)
 
 /**
   * Initialises a system wide timer, used to drive the various components used in the runtime.
@@ -66,6 +80,13 @@ static Timer *timer = NULL;
   */
 int system_timer_init(int period)
 {
+#if CONFIG_ENABLED( MICROBIT_TICK64)
+    if ( ticker == NULL)
+    {
+        ticker = new Ticker();
+        microbit_tick64_initialise();
+    }
+#else
     if (ticker == NULL)
         ticker = new Ticker();
 
@@ -74,6 +95,7 @@ int system_timer_init(int period)
         timer = new Timer();
         timer->start();
     }
+#endif
 
     return system_timer_set_period(period);
 }
@@ -119,12 +141,19 @@ int system_timer_get_period()
   */
 void update_time()
 {
+#if CONFIG_ENABLED( MICROBIT_TICK64)
+    if ( ticker == NULL)
+        system_timer_init(SYSTEM_TICK_PERIOD_MS);
+    else
+        microbit_tick64_update();
+#else
     // If we haven't been initialized, bring up the timer with the default period.
     if (timer == NULL || ticker == NULL)
         system_timer_init(SYSTEM_TICK_PERIOD_MS);
 
     time_us += timer->read_us();
     timer->reset();
+#endif
 }
 
 /**
@@ -144,8 +173,15 @@ uint64_t system_timer_current_time()
   */
 uint64_t system_timer_current_time_us()
 {
+#if CONFIG_ENABLED( MICROBIT_TICK64)
+    if ( ticker == NULL)
+        system_timer_init(SYSTEM_TICK_PERIOD_MS);
+
+    return microbit_tick64_microseconds();
+#else
     update_time();
     return time_us;
+#endif
 }
 
 /**
@@ -179,7 +215,11 @@ int system_timer_add_component(MicroBitComponent *component)
     int i = 0;
 
     // If we haven't been initialized, bring up the timer with the default period.
+#if CONFIG_ENABLED( MICROBIT_TICK64)
+    if ( ticker == NULL)
+#else
     if (timer == NULL || ticker == NULL)
+#endif
         system_timer_init(SYSTEM_TICK_PERIOD_MS);
 
     while(systemTickComponents[i] != NULL && i < MICROBIT_SYSTEM_COMPONENTS)

source/core/MicroBitTick64.cpp

@@ -0,0 +1,37 @@
+/*
+The MIT License (MIT)
+
+Copyright (c) 2020 Insight Resources
+
+Permission is hereby granted, free of charge, to any person obtaining a
+copy of this software and associated documentation files (the "Software"),
+to deal in the Software without restriction, including without limitation
+the rights to use, copy, modify, merge, publish, distribute, sublicense,
+and/or sell copies of the Software, and to permit persons to whom the
+Software is furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in
+all copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
+THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
+DEALINGS IN THE SOFTWARE.
+*/
+
+#include "MicroBitTick64.h"
+
+
+microbit_tick64_t  microbit_tick640;
+microbit_tick64_t  microbit_tick641;
+microbit_tick64_t *microbit_tick64;
+
+
+//#if CONFIG_ENABLED(MICROBIT_DBG)
+//const uint32_t microbit_tick64_highunit = 0x10000;
+//#else
+const uint32_t microbit_tick64_highunit = 0x80000000ul;
+//#endif