- Unecessary definitions are removed.
- Since the 48-bit RTC hardware timer uses a RC oscillator as clock, it is pretty inaccurate and leads to a RTC time deviation of up to 3 seconds per minute. Therefore, a calibration during the boot time determines a correction factor for the 48-bit RTC hardware timer. Function _rtc_time_to_us uses now this correction factor and converts a raw 48-bit RTC time to a corrected time in microseconds. Thus, the 48-bit RTC timer becomes much more accurate, but it can't still reach the accuracy of the PLL driven 64-bit system timer. The Advantage of using RTC over 64-bit sydtem timer is that it also continues in deep sleep mode and after software reset.
- If the 64-bit system timer is used to emulate the RTC timer, it uses the RTC hardware timer to continue its operation after software .
It is possible to use different timers as RTC timer for the periph_rtc module. Either the 48-bit RTC hardware timer is used directly or the PLL driven 64-bit system timer emulates a RTC timer. The latter one is much more accurate. Pseudomodule esp_rtc_timer controlls which timer is used. Only if esp_rtc_timer is enabled explicitly, the 48-bit RTC hardware timer is used. Otherwise the 64-bit sytstem timer is used to emulate the RTC timer.
The explicit call of rtc_init during the CPU start was removed because rtc_init is called within the function periph_init. The display of the system time at startup had to be placed after the call to periph_init.
There is an existing function that returns the system time in us as a 64 bit value. Converting this 64 value in us to a 32 bit value in ms is more easier and uses the complete 32 bit range. Using only the low part of the 64 bit system time in us and dividing it by 1e3 cuts the 32 bit range.
The buffer[EHTHERNET_MAX_LEN] used in _esp_wifi_send to convert the iolist of the given packet to a plain buffer for the WiFi interface should not be on the stack to prevent the sending thread's stack from overflowing.
Some ESP8266/ESP8285 modules only work with DOUT SPI flash mode and a SPI flash frequency of 26 MHz. Therefore, these parameters have to be used by default. Otherwise some modules will no boot.
