b85011c15f
Add Kconfig option SPIRAM_ALLOW_NOINIT_EXTERNAL_MEMORY When enabled, a new linker script rule (from esp32.extram.noinit.ld) places any variables in the .ext_ram.noinit section in SPIRAM. This section is exempted from the startup SPIRAM memory test and is not zero-initialized or added to the malloc pool, making it usable for noinit variables that persist across reset. The EXT_RAM_NOINIT_ATTR macro places variables in this section.
System Notes
Timekeeping
The following are the timekeeping mechanisms available and their differences:
- System time (
esp_system_get_time)
Time with the origin at g_startup_time. The implementation is not handled by esp_system,
but it does provide a default implementation using RTC timer. Currently, esp_timer
provides system time, since the hardware timers are under the control of that
component. However, no matter the underlying timer, the system time provider
should maintain the definition of having the origin point at g_startup_time.
esp_timertime (esp_timer_get_time)
This is the time read from an underlying hardware timer, controlled through config. Origin is at the point where the underlying timer starts counting.
newlibtime (gettimeofday)
Timekeeping function in standard library. Can be set (settimeofday) or moved forward/backward (adjtime);
with the possibility of the changes being made persistent through config.
Currently implemented in terms of system time, as the point of origin is fixed.
If persistence is enabled, RTC time is also used in conjuction with system time.
- RTC time (
esp_rtc_get_time_us)
Time read from RTC timer.