- 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.
ROM code already implements XTAL frequency detection, but it uses the 8M
clock before the clock tuning parameters are initialized. With the
zero clock tuning parameter, 8M clock has significant frequency deviation
at high temperatures, which can lead to erroneous detection of 40 MHz
crystal as a 26 MHz one.
This change adds XTAL frequency detection code to rtc_clk_init routine,
and detection is performed after the 8M clock tuning parameter as been
initialized.
On first reset, ROM code writes the estimated XTAL frequency into
RTC_APB_FREQ_REG (aka STORE5). If the application doesn’t specify exact
XTAL frequency (which is always the case for now), rtc_clk_init will
guess what kind of XTAL is used (26M or 40M), based on the estimated
frequency. Later, detected frequency is written into RTC_XTAL_FREQ_REG
(aka STORE4).
When the application switches clock source to PLL, APB frequency changes
and RTC_APB_FREQ_REG is updated. If the application encounters an RTC
WDT reset, RTC_APB_FREQ_REG will not be updated prior to reset. Once the
application starts up again, it will attempt to auto-detect XTAL
frequency based on RTC_APB_FREQ_REG, which now has value of 80000000.
This will fail, and rtc_clk_xtal_freq_estimate will fall back to the
default value of 26 MHz. Due to an incorrect XTAL frequency, PLL
initialization will also take incorrect path, and PLL will run at a
different frequency. Depending on the application this may cause just
garbage output on UART or a crash (if WiFi is used).
