Also, re-enable calibration storage for CircuitPlayground Express.
Tested with a 500hz PWMOut on Metro M0 with Saleae:
* with crystal 500hz
* with usb 500hz +- 0.1hz
* without either 487hz += 0.1hz
SAMD51 is skipped due to DFLL errata and the fact it defaults to a
factory calibrated 48mhz that works fine for USB.
Fixes#648
This uses the crystal to clock the RTC on boards which have a crystal.
Disable clock generator 2 which was enabled in commit
8e2080411f ("atmel-samd: Add rtc module support").
samd51 differs from samd21 when it comes to the RTC clock. samd51 doesn't
have an explicit clock peripheral so no need for a clock generator.
The same commit didn't even setup XOSC32K correctly, it missed EN1K and XTALEN.
The RTC uses the 1k clock output, so enable it on the OSCULP32K even if it works without it.
Refactor the convoluted asf4 clock setup into something more readable.
enable_clock_generator() has 2 changes:
- Set 'Output enabled' to match the current clock setup
- Handle divisors above 511
Add an enable_clock_generator_sync() version which makes it possible to setup
clocks without waiting for syncing. The bootup would hang without this.
I have checked these registers:
NVMCTRL->CTRLA = 0x00000004
Peripheral clocks (only non-zero shown):
PCHCTRL[1]=0x00000045
PCHCTRL[10]=0x00000041
Generator clocks (only non-zero shown):
GENCTRL[0] = 0x00010907
GENCTRL[1] = 0x00010906
-GENCTRL[2] = 0x00041104
+GENCTRL[2] = 0x00200904
GENCTRL[4] = 0x00010907
GENCTRL[5] = 0x00180906
DFLL clock:
OSCCTRL->DFLLCTRLA = 0x00000082
OSCCTRL->DFLLCTRLB = 0x00000000
OSCCTRL->DFLLVAL = 0x00008082
OSCCTRL->DFLLMUL = 0x00000000
DPLL clocks:
OSCCTRL->Dpll[0].DPLLCTRLA=0x00000002
OSCCTRL->Dpll[0].DPLLCTRLB=0x00000000
OSCCTRL->Dpll[0].DPLLRATIO=0x0000003b
OSCCTRL->Dpll[1].DPLLCTRLA=0x00000080
OSCCTRL->Dpll[1].DPLLCTRLB=0x00000020
OSCCTRL->Dpll[1].DPLLRATIO=0x00000000
OSC32KCTRL clock:
OSC32KCTRL->RTCCTRL = 0x00000000
OSC32KCTRL->XOSC32K = 0x00002082
OSC32KCTRL->CFDCTRL = 0x00000000
OSC32KCTRL->EVCTRL = 0x00000000
OSC32KCTRL->OSCULP32K = 0x00002300
Only gen2 changed which is due to samd51 having more bits in the simple
division register so DIVSEL wasn't necessary, and it didn't have OE set.
