内核中的 Data watchpoint and Trace unit (DWT) 可以实现指令数的测量。具体实现过程如下
内核中有DWT_CYCCNT，DWT_CPICNT，DWT_EXCCNT，DWT_SLEEPCNT，DWT_LSUCNT，DWT_FOLDCNT 六个寄存器。
除了DWT_CYCCNT以外，其它寄存器都是8位的，若溢出测导致测量结果不准确。 所以只适用于少量代码指令数的测量。
指令数 instruction count 可以通过如下公式结算得出。
?具体code 实现过程如下，主要是测量方法和需要配置的内核寄存器。
#define REG_READ(addr) ? ? ? ?*((volatile u32 *)addr)
#define REG_WRITE(addr, val) ?*((volatile u32 *)addr) = (val)
/* cortex-m7 debug system register */
#define DEMCR ? ? ? ?0xE000EDFC
#define DEMCR_TRCENA ? ?(1UL << 24)
#define DWT_CTRL_CYCCNTENA ? (1UL << 0)?
#define DWT_CTRL_CPIEVTENA ? (1UL << 17)
#define DWT_CTRL_EXCEVTENA ? (1UL << 18)
#define DWT_CTRL_SLEEPEVTENA (1UL << 19)
#define DWT_CTRL_LSUEVTENA ? (1UL << 20)
#define DWT_CTRL_FOLDEVTENA ?(1UL << 21)
#define PMU_READ_CYCLE() ? ? ? ?REG_READ(DWT_CYCCNT) + \
? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? REG_READ(DWT_FOLDCNT) - \
?? ??? ??? ??? ??? ??? ??? ??? ?REG_READ(DWT_LSUCNT) - \
?? ??? ??? ??? ??? ??? ??? ??? ?REG_READ(DWT_EXCCNT) - \
?? ??? ??? ??? ??? ??? ??? ??? ?REG_READ(DWT_SLEEPCNT) - \
?? ??? ??? ??? ??? ??? ??? ??? ?REG_READ(DWT_CPICNT)
struct perf_event {
?? ?u32 count;
?? ?u32 prev_count;
};
void pmu_enable(void)
{
?? ?u32 val;
?? ?val = REG_READ(DEMCR);
?? ?REG_WRITE(DEMCR, (val | DEMCR_TRCENA));
}
?
void pmu_event_start()
{
?? ?u32 val;?? ?
? ? val = REG_READ(DWT_CTRL);
??? REG_WRITE(DWT_CTRL, (val | DWT_CTRL_CYCCNTENA |
?? ??? ??? ?DWT_CTRL_CPIEVTENA |
?? ??? ??? ?DWT_CTRL_EXCEVTENA |
?? ??? ??? ?DWT_CTRL_SLEEPEVTENA |
?? ??? ??? ?DWT_CTRL_LSUEVTENA |
?? ??? ??? ?DWT_CTRL_FOLDEVTENA));
}
void pmu_event_stop()
{
?? ?u32 val;
?? ?val = REG_READ(DWT_CTRL);
?? ?REG_WRITE(DWT_CTRL, (val &?
?? ??? ??? ?~(DWT_CTRL_CYCCNTENA |
?? ??? ??? ? ?DWT_CTRL_CPIEVTENA |
?? ??? ??? ? ?DWT_CTRL_EXCEVTENA |
?? ??? ??? ? ?DWT_CTRL_SLEEPEVTENA |
?? ??? ??? ? ?DWT_CTRL_LSUEVTENA |
?? ??? ??? ? ?DWT_CTRL_FOLDEVTENA)));
}
void pmu_event_read(struct perf_event *event)
{
?? ?u32 curr;
?? ?curr = PMU_READ_CYCLE();
?? ?event->count = curr - event->prev_count;
?? ?event->prev_count = curr;
}
main()
{
....
struct perf_event perf_evts;
pmu_event_start();
pmu_event_read(&perf_evts);
function(); /*需要测试指令数的代码? */
pmu_event_read(&perf_evts);
pmu_event_stop();
printf(">>>%d is ICNT <<<.\n", perf_evts.count);
...
}