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samd/clock_config: Document the #defines use in init_clocks().

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Which may be set in the respective mpconfigboard.h files.
This commit is contained in:
robert-hh 2022-08-13 17:33:04 +02:00 committed by Damien George
parent f0399d35e4
commit ddd41b8bbf
2 changed files with 74 additions and 0 deletions
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34
ports/samd/mcu/samd21/clock_config.c
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@ -96,6 +96,40 @@ void check_usb_recovery_mode(void) {
#endif // MICROPY_HW_XOSC32K
}
// Purpose of the #defines for the clock configuration.
//
// Both CPU and periperal devices are clocked by the DFLL48M clock.
// DFLL48M is either free running, or controlled by the 32kHz crystal, or
// Synchronized with the USB clock.
//
// #define MICROPY_HW_XOSC32K (0 | 1)
//
// If MICROPY_HW_XOSC32K = 1, the 32kHz crystal is used as input for GCLK 1, which
// serves as refernce clock source for the DFLL48M oscillator,
// The crystal is used, unless MICROPY_HW_MCU_OSC32KULP is set.
// In that case GCLK1 (and the CPU clock) is driven by the 32K Low power oscillator.
// The reason for offering this option is a design flaw of the Adafruit
// Feather boards, where the RGB Led and Debug signals interfere with the
// crystal, causing the CPU to fail if it is driven by the crystal.
//
// If MICROPY_HW_XOSC32K = 0, the 32kHz signal for GCLK1 (and the CPU) is
// created by dividing the 48MHz clock of DFLL48M, but not used otherwise.
//
// If MICROPY_HW_DFLL_USB_SYNC = 0, the DFLL48M oscillator is free running using
// the pre-configured trim values. In that mode, the peripheral clock is
// not exactly 48Mhz and has a substantional temperature drift.
//
// If MICROPY_HW_DFLL_USB_SYNC = 1, the DFLL48 is synchronized with the 1 kHz USB sync
// signal. If after boot there is no USB sync withing 500ms, the configuratuion falls
// back to a free running 48Mhz oscillator.
//
// In all modes, the 48MHz signal has a substantial jitter, largest when
// MICROPY_HW_DFLL_USB_SYNC is active. That is caused by the repective
// reference frequencies of 32kHz or 1 kHz being low. That affects most
// PWM. Std Dev at 1kHz 0.156Hz (w. Crystal) up to 0.4 Hz (with USB sync).
//
// If none of the mentioned defines is set, the device uses the internal oscillators.
void init_clocks(uint32_t cpu_freq) {
dfll48m_calibration = 0; // please the compiler

40
ports/samd/mcu/samd51/clock_config.c
View File

@ -142,6 +142,46 @@ void check_usb_recovery_mode(void) {
#endif // MICROPY_HW_XOSC32K
}
// Purpose of the #defines for the clock configuration.
//
// The CPU clock is generated by DPLL0, which takes 32768 Hz as reference frequency,
// supplied through GCLK1.
//
// DFLL48M is used for the peripheral clock, e.g. for PWM, UART, SPI, I2C.
// DFLL48M is either free running, or controlled by the 32kHz crystal, or
// Synchronized with the USB clock.
//
// GCLK1 takes it's input either from the 32kHz crystal, the internal low power
// RC oscillator or from DFLL48M.
//
// #define MICROPY_HW_XOSC32K (0 | 1)
//
// If MICROPY_HW_XOSC32K = 1, the 32kHz crystal is used for the DFLL48M oscillator
// and for GCLK1, feeding the CPU, unless MICROPY_HW_MCU_OSC32KULP is set.
// In that case GCLK1 (and the CPU clock) is driven by the 32K Low power oscillator.
// The reason for offering this option is a design flaw of the Adafruit
// Feather boards, where the RGB Led and Debug signals interfere with the
// crystal, causing the CPU to fail if it is driven by the crystal. The
// peripheral devices are affected as well, but continue it's operation.
//
// If MICROPY_HW_XOSC32K = 0, the 32kHz signal for GCLK1 (and the CPU) is
// created by dividing the 48MHz clock of DFLL48M.
//
// If MICROPY_HW_DFLL_USB_SYNC = 0, the DFLL48M oscillator is free running using
// the pre-configured trim values. In that mode, the peripheral clock is
// not exactly 48Mhz and has a substantional temperature drift.
//
// If MICROPY_HW_DFLL_USB_SYNC = 1, the DFLL48 is synchronized with the 1 kHz USB sync
// signal. If after boot there is no USB sync withing 500ms, the configuratuion falls
// back to a free running 48Mhz oscillator.
//
// In all modes, the 48MHz signal has a substantial jitter, largest when
// MICROPY_HW_DFLL_USB_SYNC is active. That is caused by the repective
// reference frequencies of 32kHz or 1 kHz being low. That affects most
// PWM. Std Dev at 1kHz 0.156Hz (w. Crystal) up to 0.4 Hz (with USB sync).
//
// If none of the mentioned defines is set, the device uses the internal oscillators.
void init_clocks(uint32_t cpu_freq) {
dfll48m_calibration = 0; // please the compiler