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Optimize tickless tick computation 

Optimize the tick computation in the following ways:
1. Use relative time rather than absolute time
2. Replace multiplication/division pair with just multiplication
    or division:
    "* 1000000ULL / OS_TICK_FREQ"   ->   "* US_IN_TICK"
    "* OS_TICK_FREQ / 1000000"      ->   "/ US_IN_TICK"
pull/9786/head
Russ Butler 2019-02-19 19:52:53 -06:00
parent e03b3b68c1
commit d43ca21ec5
2 changed files with 16 additions and 11 deletions
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25
rtos/TARGET_CORTEX/SysTimer.cpp
View File

@ -25,6 +25,7 @@
#include "hal/lp_ticker_api.h"
#include "mbed_critical.h"
#include "mbed_assert.h"
#if defined(TARGET_CORTEX_A)
#include "rtx_core_ca.h"
#else//Cortex-M
@ -37,6 +38,9 @@ extern "C" {
#endif
}
#define US_IN_TICK (1000000 / OS_TICK_FREQ)
MBED_STATIC_ASSERT(1000000 % OS_TICK_FREQ == 0, "OS_TICK_FREQ must be a divisor of 1000000 for correct tick calculations");
#if (defined(NO_SYSTICK))
/**
* Return an IRQ number that can be used in the absence of SysTick
@ -54,17 +58,17 @@ namespace rtos {
namespace internal {
SysTimer::SysTimer() :
TimerEvent(get_lp_ticker_data()), _start_time(0), _tick(0)
TimerEvent(get_lp_ticker_data()), _time_us(0), _tick(0)
{
_start_time = ticker_read_us(_ticker_data);
_time_us = ticker_read_us(_ticker_data);
_suspend_time_passed = true;
_suspended = false;
}
SysTimer::SysTimer(const ticker_data_t *data) :
TimerEvent(data), _start_time(0), _tick(0)
TimerEvent(data), _time_us(0), _tick(0)
{
_start_time = ticker_read_us(_ticker_data);
_time_us = ticker_read_us(_ticker_data);
}
void SysTimer::setup_irq()
@ -106,16 +110,16 @@ uint32_t SysTimer::resume()
_suspend_time_passed = true;
remove();
uint64_t new_tick = (ticker_read_us(_ticker_data) - _start_time) * OS_TICK_FREQ / 1000000;
if (new_tick > _tick) {
uint64_t elapsed_ticks = (ticker_read_us(_ticker_data) - _time_us) / US_IN_TICK;
if (elapsed_ticks > 0) {
// Don't update to the current tick. Instead, update to the
// previous tick and let the SysTick handler increment it
// to the current value. This allows scheduling restart
// successfully after the OS is resumed.
new_tick--;
elapsed_ticks--;
}
uint32_t elapsed_ticks = new_tick - _tick;
_tick = new_tick;
_time_us += elapsed_ticks * US_IN_TICK;
_tick += elapsed_ticks;
core_util_critical_section_exit();
return elapsed_ticks;
@ -125,7 +129,7 @@ void SysTimer::schedule_tick(uint32_t delta)
{
core_util_critical_section_enter();
insert_absolute(_start_time + (_tick + delta) * 1000000ULL / OS_TICK_FREQ);
insert_absolute(_time_us + delta * US_IN_TICK);
core_util_critical_section_exit();
}
@ -171,6 +175,7 @@ void SysTimer::_increment_tick()
// Protected function synchronized externally
_tick++;
_time_us += US_IN_TICK;
}
void SysTimer::handler()

2
rtos/TARGET_CORTEX/SysTimer.h
View File

@ -117,7 +117,7 @@ protected:
virtual void handler();
void _increment_tick();
static void _set_irq_pending();
us_timestamp_t _start_time;
us_timestamp_t _time_us;
uint64_t _tick;
bool _suspend_time_passed;
bool _suspended;