Comparison of various delay methods(转载)

最新推荐文章于 2025-05-01 06:30:00 发布

tomy9527

最新推荐文章于 2025-05-01 06:30:00 发布

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分类专栏： ESS VCD 文章标签： delay methods reference timer loops access

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本文转载了多种延迟方法的比较内容。介绍了risc_sleep_a_bit、“bank3safe”、UTIL_xxx_timer2_end、“glbTimer”等方法的精度、限制及使用示例。同时指出纯“for”循环因缓存命中/未命中不一致，不是可靠的延迟方法。

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Comparison of various delay methods(转载)

(1) risc_sleep_a_bit(n)
- accuracy within ~13ns when n>20.
- limitation: n < cycles in timer2_period (0.5 second).

(2) "bank3safe"
    - accuracy within bank3 WS, ~100ns(byte access)
    - usage example:
    void foo(void)
    {
        volatile unsigned int *ptrdelay = (unsigned int *) bank3safe;
.
.
(void) *ptrdelay; /* DW access = ~400ns(4*100) delay */
.
.
    }

(3) UTIL_xxx_timer2_end()
    - accuracy is similar to risc_sleep_a_bit(), but intended for delays
      greater than ~1us.
    - usage example:
      (please reference SERVO_delay_n_ms() in servos.c or
       VFD_schedule_state_change() in microvfd.c)

(4) "glbTimer"
- accuracy within ~200ms - ~500ms depending on frequency of
"glbTimer" checks.

NOTE: pure "for" loops are NOT reliable delay methods because of
cache hit/miss inconsistencies.