Even though RTC_CLK_CONFIG_DEFAULT correctly had RTC_FAST_FREQ_8M as the
fast clock, the bootloader modified fast_freq field to the currently
selected RTC_FAST_CLK (so that the clock choice is not affected by the
bootloader). The application startup code never switched to 8M clock,
which caused the default (XTAL/4) to be used as RTC_FAST_CLK. This had
caused a number of issues, such as touch pads not working in deep sleep.
Fixes https://github.com/espressif/esp-idf/issues/542.
Ref TW12053.
- RTC_CNTL_SLOWCLK_FREQ define is removed; rtc_clk_slow_freq_get_hz
function can be used instead to get an approximate RTC_SLOW_CLK
frequency
- Clock calibration is performed at startup. The value is saved and used
for timekeeping and when entering deep sleep.
- When using the 32k XTAL, startup code will wait for the oscillator to
start up. This can be possibly optimized by starting a separate task
to wait for oscillator startup, and performing clock switch in that
task.
- Fix a bug that 32k XTAL would be disabled in rtc_clk_init.
- Fix a rounding error in rtc_clk_cal, which caused systematic frequency
error.
- Fix an overflow bug which caused rtc_clk_cal to timeout early if the
slow_clk_cycles argument would exceed certain value
- Improve 32k XTAL oscillator startup time by introducing bootstrapping
code, which uses internal pullup/pulldown resistors on 32K_N/32K_P
pins to set better initial conditions for the oscillator.
