HAL_ChibiOS: support starting the clock at non-zero

for testing time wrap bugs

libraries/AP_HAL_ChibiOS/hwdef/common/chibios_board.mk

@@ -243,6 +243,10 @@ ifeq ($(ENABLE_STATS),yes)
  ASXFLAGS += -DHAL_ENABLE_THREAD_STATISTICS
 endif
 
+ifneq ($(AP_BOARD_START_TIME),)
+ UDEFS += -DAP_BOARD_START_TIME=$(AP_BOARD_START_TIME)
+endif
+
 # Define ASM defines here
 UADEFS =
 

libraries/AP_HAL_ChibiOS/hwdef/common/hrt.c

@@ -75,6 +75,9 @@ static uint32_t get_systime_us32(void)
 {
     static uint32_t last_us32;
     uint32_t now = system_time_u32_us();
+#ifdef AP_BOARD_START_TIME
+    now += AP_BOARD_START_TIME;
+#endif
     if (now < last_us32) {
         const uint64_t dt_us = 0x100000000ULL;
         timer_base_us64 += dt_us;

libraries/AP_HAL_ChibiOS/system.cpp

@@ -319,7 +319,11 @@ __FASTRAMFUNC__ uint32_t micros()
 {
 #if CH_CFG_ST_RESOLUTION == 32 && CH_CFG_ST_FREQUENCY==1000000U
     // special case optimisation for 32 bit timers
+#ifdef AP_BOARD_START_TIME
+    return st_lld_get_counter() + AP_BOARD_START_TIME;
+#else
     return st_lld_get_counter();
+#endif
 #else
     return hrt_micros32();
 #endif