Ivan Grokhotkov 5b54ae76d4 esp_timer, hal: add support for non-integer systimer frequency ... When ESP32-C2 is paired with a 26 MHz XTAL, the systimer tick frequency becomes equal to 26 / 2.5 = 10.4 MHz. Previously we always assumed that systimer tick frequency is integer (and 1 MHz * power of two, above that!). This commit introduces a new LL macro, SYSTIMER_LL_TICKS_PER_US_DIV. It should be set in such a way that: 1. SYSTIMER_LL_TICKS_PER_US / SYSTIMER_LL_TICKS_PER_US_DIV equals the actual systimer tick frequency, 2. and SYSTIMER_LL_TICKS_PER_US is integer. For ESP32-C2 this means that SYSTIMER_LL_TICKS_PER_US = 52 and SYSTIMER_LL_TICKS_PER_US_DIV = 5. This introduced two possible issues: 1. Overflow when multiplying systimer counter by 5 - Should not be an issue, since systimer counter is 52-bit, so counter * 5 is no more than 55-bit. 2. The code needs to perform: - divide by 5: when converting from microseconds to ticks - divide by 52: when converting from ticks to microseconds The latter potentially introduces a performance issue for the esp_timer_get_time function.		2022-07-11 12:24:37 +08:00
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hal	esp_timer, hal: add support for non-integer systimer frequency	2022-07-11 12:24:37 +08:00