108 lines
4.0 KiB
C
108 lines
4.0 KiB
C
#include <ch.h>
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#include "timer.h"
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static uint32_t ticks_offset = 0;
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static uint32_t last_ticks = 0;
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static uint32_t ms_offset = 0;
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#if CH_CFG_ST_RESOLUTION < 32
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static uint32_t last_systime = 0;
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static uint32_t overflow = 0;
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#endif
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// Get the current system time in ticks as a 32-bit number.
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// This function must be called from within a system lock zone (so that it can safely use and update the static data).
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static inline uint32_t get_system_time_ticks(void) {
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uint32_t systime = (uint32_t)chVTGetSystemTimeX();
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#if CH_CFG_ST_RESOLUTION < 32
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// If the real system timer resolution is less than 32 bits, provide the missing bits by checking for the counter
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// overflow. For this to work, this function must be called at least once for every overflow of the system timer.
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// In the 16-bit case, the corresponding times are:
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// - CH_CFG_ST_FREQUENCY = 100000, overflow will occur every ~0.65 seconds
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// - CH_CFG_ST_FREQUENCY = 10000, overflow will occur every ~6.5 seconds
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// - CH_CFG_ST_FREQUENCY = 1000, overflow will occur every ~65 seconds
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if (systime < last_systime) {
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overflow += ((uint32_t)1) << CH_CFG_ST_RESOLUTION;
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}
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last_systime = systime;
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systime += overflow;
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#endif
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return systime;
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}
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#if CH_CFG_ST_RESOLUTION < 32
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static virtual_timer_t update_timer;
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// Update the system tick counter every half of the timer overflow period; this should keep the tick counter correct
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// even if something blocks timer interrupts for 1/2 of the timer overflow period.
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# define UPDATE_INTERVAL (((sysinterval_t)1) << (CH_CFG_ST_RESOLUTION - 1))
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// VT callback function to keep the overflow bits of the system tick counter updated.
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static void update_fn(void *arg) {
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(void)arg;
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chSysLockFromISR();
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get_system_time_ticks();
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chVTSetI(&update_timer, UPDATE_INTERVAL, update_fn, NULL);
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chSysUnlockFromISR();
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}
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#endif
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// The highest multiple of CH_CFG_ST_FREQUENCY that fits into uint32_t. This number of ticks will necessarily
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// correspond to some integer number of seconds.
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#define OVERFLOW_ADJUST_TICKS ((uint32_t)((UINT32_MAX / CH_CFG_ST_FREQUENCY) * CH_CFG_ST_FREQUENCY))
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// The time in milliseconds which corresponds to OVERFLOW_ADJUST_TICKS ticks (this is a precise conversion, because
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// OVERFLOW_ADJUST_TICKS corresponds to an integer number of seconds).
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#define OVERFLOW_ADJUST_MS (TIME_I2MS(OVERFLOW_ADJUST_TICKS))
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void timer_init(void) {
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timer_clear();
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#if CH_CFG_ST_RESOLUTION < 32
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chVTObjectInit(&update_timer);
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chVTSet(&update_timer, UPDATE_INTERVAL, update_fn, NULL);
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#endif
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}
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void timer_clear(void) {
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chSysLock();
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ticks_offset = get_system_time_ticks();
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last_ticks = 0;
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ms_offset = 0;
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chSysUnlock();
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}
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uint16_t timer_read(void) {
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return (uint16_t)timer_read32();
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}
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uint32_t timer_read32(void) {
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chSysLock();
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uint32_t ticks = get_system_time_ticks() - ticks_offset;
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if (ticks < last_ticks) {
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// The 32-bit tick counter overflowed and wrapped around. We cannot just extend the counter to 64 bits here,
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// because TIME_I2MS() may encounter overflows when handling a 64-bit argument; therefore the solution here is
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// to subtract a reasonably large number of ticks from the tick counter to bring its value below the 32-bit
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// limit again, and then add the equivalent number of milliseconds to the converted value. (Adjusting just the
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// converted value to account for 2**32 ticks is not possible in general, because 2**32 ticks may not correspond
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// to an integer number of milliseconds).
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ticks -= OVERFLOW_ADJUST_TICKS;
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ticks_offset += OVERFLOW_ADJUST_TICKS;
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ms_offset += OVERFLOW_ADJUST_MS;
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}
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last_ticks = ticks;
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uint32_t ms_offset_copy = ms_offset; // read while still holding the lock to ensure a consistent value
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chSysUnlock();
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return (uint32_t)TIME_I2MS(ticks) + ms_offset_copy;
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}
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uint16_t timer_elapsed(uint16_t last) {
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return TIMER_DIFF_16(timer_read(), last);
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}
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uint32_t timer_elapsed32(uint32_t last) {
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return TIMER_DIFF_32(timer_read32(), last);
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}
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