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-rw-r--r--platforms/chibios/timer.c100
1 files changed, 77 insertions, 23 deletions
diff --git a/platforms/chibios/timer.c b/platforms/chibios/timer.c
index 9f664e1f79..74fdd7a6fc 100644
--- a/platforms/chibios/timer.c
+++ b/platforms/chibios/timer.c
@@ -2,44 +2,98 @@
#include "timer.h"
-static uint32_t reset_point = 0;
+static uint32_t ticks_offset = 0;
+static uint32_t last_ticks = 0;
+static uint32_t ms_offset = 0;
#if CH_CFG_ST_RESOLUTION < 32
static uint32_t last_systime = 0;
static uint32_t overflow = 0;
#endif
-void timer_init(void) { timer_clear(); }
-
-void timer_clear(void) {
- reset_point = (uint32_t)chVTGetSystemTime();
-#if CH_CFG_ST_RESOLUTION < 32
- last_systime = reset_point;
- overflow = 0;
-#endif
-}
-
-uint16_t timer_read(void) { return (uint16_t)timer_read32(); }
-
-uint32_t timer_read32(void) {
- uint32_t systime = (uint32_t)chVTGetSystemTime();
+// Get the current system time in ticks as a 32-bit number.
+// This function must be called from within a system lock zone (so that it can safely use and update the static data).
+static inline uint32_t get_system_time_ticks(void) {
+ uint32_t systime = (uint32_t)chVTGetSystemTimeX();
#if CH_CFG_ST_RESOLUTION < 32
- // If/when we need to support 64-bit chips, this may need to be modified to match the native bit-ness of the MCU.
- // At this point, the only SysTick resolution allowed other than 32 is 16 bit.
- // In the 16-bit case, at:
+ // If the real system timer resolution is less than 32 bits, provide the missing bits by checking for the counter
+ // overflow. For this to work, this function must be called at least once for every overflow of the system timer.
+ // In the 16-bit case, the corresponding times are:
// - CH_CFG_ST_FREQUENCY = 100000, overflow will occur every ~0.65 seconds
// - CH_CFG_ST_FREQUENCY = 10000, overflow will occur every ~6.5 seconds
// - CH_CFG_ST_FREQUENCY = 1000, overflow will occur every ~65 seconds
- // With this implementation, as long as we ensure a timer read happens at least once during the overflow period, timing should be accurate.
if (systime < last_systime) {
overflow += ((uint32_t)1) << CH_CFG_ST_RESOLUTION;
}
-
last_systime = systime;
- return (uint32_t)TIME_I2MS(systime - reset_point + overflow);
-#else
- return (uint32_t)TIME_I2MS(systime - reset_point);
+ systime += overflow;
#endif
+
+ return systime;
+}
+
+#if CH_CFG_ST_RESOLUTION < 32
+static virtual_timer_t update_timer;
+
+// Update the system tick counter every half of the timer overflow period; this should keep the tick counter correct
+// even if something blocks timer interrupts for 1/2 of the timer overflow period.
+# define UPDATE_INTERVAL (((sysinterval_t)1) << (CH_CFG_ST_RESOLUTION - 1))
+
+// VT callback function to keep the overflow bits of the system tick counter updated.
+static void update_fn(void *arg) {
+ (void)arg;
+ chSysLockFromISR();
+ get_system_time_ticks();
+ chVTSetI(&update_timer, UPDATE_INTERVAL, update_fn, NULL);
+ chSysUnlockFromISR();
+}
+#endif
+
+// The highest multiple of CH_CFG_ST_FREQUENCY that fits into uint32_t. This number of ticks will necessarily
+// correspond to some integer number of seconds.
+#define OVERFLOW_ADJUST_TICKS ((uint32_t)((UINT32_MAX / CH_CFG_ST_FREQUENCY) * CH_CFG_ST_FREQUENCY))
+
+// The time in milliseconds which corresponds to OVERFLOW_ADJUST_TICKS ticks (this is a precise conversion, because
+// OVERFLOW_ADJUST_TICKS corresponds to an integer number of seconds).
+#define OVERFLOW_ADJUST_MS (TIME_I2MS(OVERFLOW_ADJUST_TICKS))
+
+void timer_init(void) {
+ timer_clear();
+#if CH_CFG_ST_RESOLUTION < 32
+ chVTObjectInit(&update_timer);
+ chVTSet(&update_timer, UPDATE_INTERVAL, update_fn, NULL);
+#endif
+}
+
+void timer_clear(void) {
+ chSysLock();
+ ticks_offset = get_system_time_ticks();
+ last_ticks = 0;
+ ms_offset = 0;
+ chSysUnlock();
+}
+
+uint16_t timer_read(void) { return (uint16_t)timer_read32(); }
+
+uint32_t timer_read32(void) {
+ chSysLock();
+ uint32_t ticks = get_system_time_ticks() - ticks_offset;
+ if (ticks < last_ticks) {
+ // The 32-bit tick counter overflowed and wrapped around. We cannot just extend the counter to 64 bits here,
+ // because TIME_I2MS() may encounter overflows when handling a 64-bit argument; therefore the solution here is
+ // to subtract a reasonably large number of ticks from the tick counter to bring its value below the 32-bit
+ // limit again, and then add the equivalent number of milliseconds to the converted value. (Adjusting just the
+ // converted value to account for 2**32 ticks is not possible in general, because 2**32 ticks may not correspond
+ // to an integer number of milliseconds).
+ ticks -= OVERFLOW_ADJUST_TICKS;
+ ticks_offset += OVERFLOW_ADJUST_TICKS;
+ ms_offset += OVERFLOW_ADJUST_MS;
+ }
+ last_ticks = ticks;
+ uint32_t ms_offset_copy = ms_offset; // read while still holding the lock to ensure a consistent value
+ chSysUnlock();
+
+ return (uint32_t)TIME_I2MS(ticks) + ms_offset_copy;
}
uint16_t timer_elapsed(uint16_t last) { return TIMER_DIFF_16(timer_read(), last); }