diff options
Diffstat (limited to 'src/atsamd/clock.c')
| -rw-r--r-- | src/atsamd/clock.c | 77 |
1 files changed, 77 insertions, 0 deletions
diff --git a/src/atsamd/clock.c b/src/atsamd/clock.c new file mode 100644 index 00000000..ef0cd9bc --- /dev/null +++ b/src/atsamd/clock.c @@ -0,0 +1,77 @@ +// Code to setup peripheral clocks on the SAMD21 +// +// Copyright (C) 2018 Kevin O'Connor <kevin@koconnor.net> +// +// This file may be distributed under the terms of the GNU GPLv3 license. + +#include "autoconf.h" // CONFIG_CLOCK_FREQ +#include "compiler.h" // DIV_ROUND_CLOSEST +#include "internal.h" // enable_pclock +#include "samd21.h" // GCLK + +// The "generic clock generators" that are configured +#define CLKGEN_MAIN 0 +#define CLKGEN_32K 1 +#define CLKGEN_ULP32K 2 + +// Enable a peripheral clock and power to that peripheral +void +enable_pclock(uint32_t clock_id, uint32_t pmask) +{ + GCLK->CLKCTRL.reg = (GCLK_CLKCTRL_ID(clock_id) + | GCLK_CLKCTRL_GEN(CLKGEN_MAIN) | GCLK_CLKCTRL_CLKEN); + while (GCLK->STATUS.reg & GCLK_STATUS_SYNCBUSY) + ; + PM->APBCMASK.reg |= pmask; +} + +#define FREQ_XOSC32K 32768 + +void +SystemInit(void) +{ + // Setup flash to work with 48Mhz clock + NVMCTRL->CTRLB.reg = NVMCTRL_CTRLB_RWS_HALF; + + // Enable external 32Khz crystal + uint32_t val = (SYSCTRL_XOSC32K_STARTUP(6) + | SYSCTRL_XOSC32K_XTALEN | SYSCTRL_XOSC32K_EN32K); + SYSCTRL->XOSC32K.reg = val; + SYSCTRL->XOSC32K.reg = val | SYSCTRL_XOSC32K_ENABLE; + while (!(SYSCTRL->PCLKSR.reg & SYSCTRL_PCLKSR_XOSC32KRDY)) + ; + + // Reset GCLK + GCLK->CTRL.reg = GCLK_CTRL_SWRST; + while (GCLK->CTRL.reg & GCLK_CTRL_SWRST) + ; + + // Route external 32Khz clock to DFLL48M (via CLKGEN_32K) + GCLK->GENDIV.reg = GCLK_GENDIV_ID(CLKGEN_32K); + GCLK->GENCTRL.reg = (GCLK_GENCTRL_ID(CLKGEN_32K) + | GCLK_GENCTRL_SRC_XOSC32K | GCLK_GENCTRL_GENEN); + GCLK->CLKCTRL.reg = (GCLK_CLKCTRL_ID(SYSCTRL_GCLK_ID_DFLL48) + | GCLK_CLKCTRL_GEN(CLKGEN_32K) | GCLK_CLKCTRL_CLKEN); + while (GCLK->STATUS.reg & GCLK_STATUS_SYNCBUSY) + ; + + // Configure DFLL48M clock + SYSCTRL->DFLLCTRL.reg = 0; + uint32_t mul = DIV_ROUND_CLOSEST(CONFIG_CLOCK_FREQ, FREQ_XOSC32K); + SYSCTRL->DFLLMUL.reg = (SYSCTRL_DFLLMUL_CSTEP(31) + | SYSCTRL_DFLLMUL_FSTEP(511) + | SYSCTRL_DFLLMUL_MUL(mul)); + SYSCTRL->DFLLCTRL.reg = (SYSCTRL_DFLLCTRL_MODE | SYSCTRL_DFLLCTRL_WAITLOCK + | SYSCTRL_DFLLCTRL_QLDIS + | SYSCTRL_DFLLCTRL_ENABLE); + uint32_t ready = (SYSCTRL_PCLKSR_DFLLRDY | SYSCTRL_PCLKSR_DFLLLCKC + | SYSCTRL_PCLKSR_DFLLLCKF); + while ((SYSCTRL->PCLKSR.reg & ready) != ready) + ; + + // Switch main clock to DFLL48M clock + GCLK->GENDIV.reg = GCLK_GENDIV_ID(CLKGEN_MAIN); + GCLK->GENCTRL.reg = (GCLK_GENCTRL_ID(CLKGEN_MAIN) + | GCLK_GENCTRL_SRC_DFLL48M + | GCLK_GENCTRL_IDC | GCLK_GENCTRL_GENEN); +} |