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atsamd: Add support for reference clock selection to SAMD21 

Add support for using the internal clocks (with USB clock recovery
mode if available) on the SAMD21.  Don't use the internal clock if the
external crystal is requested (instead use the PLL synced to the
external 32Khz signal).

Signed-off-by: Kevin O'Connor <kevin@koconnor.net>
This commit is contained in:
Kevin O'Connor 2019-02-21 12:32:51 -05:00
parent d452a1de48
commit da68da7a63
2 changed files with 59 additions and 28 deletions
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1
src/atsamd/Kconfig
View File

@ -54,7 +54,6 @@ config CLOCK_FREQ
default 120000000 if MACH_SAMD51
choice
depends on MACH_SAMD51
prompt "Clock Reference"
config CLOCK_REF_INTERNAL
bool "Internal clock"

86
src/atsamd/clock.c
View File

@ -9,7 +9,6 @@
// The "generic clock generators" that are configured
#define CLKGEN_MAIN 0
#define CLKGEN_32K 1
#define CLKGEN_ULP32K 2
#define FREQ_MAIN 48000000
@ -49,6 +48,60 @@ get_pclock_frequency(uint32_t pclk_id)
return FREQ_MAIN;
}
// Initialize the clocks using an external 32K crystal
static void
clock_init_32k(void)
{
// 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))
;
// Generate 48Mhz clock on DPLL (with XOSC32K as reference)
SYSCTRL->DPLLCTRLA.reg = 0;
uint32_t mul = DIV_ROUND_CLOSEST(FREQ_MAIN, FREQ_32K);
SYSCTRL->DPLLRATIO.reg = SYSCTRL_DPLLRATIO_LDR(mul - 1);
SYSCTRL->DPLLCTRLB.reg = SYSCTRL_DPLLCTRLB_LBYPASS;
SYSCTRL->DPLLCTRLA.reg = SYSCTRL_DPLLCTRLA_ENABLE;
uint32_t mask = SYSCTRL_DPLLSTATUS_CLKRDY | SYSCTRL_DPLLSTATUS_LOCK;
while ((SYSCTRL->DPLLSTATUS.reg & mask) != mask)
;
// Switch main clock to DPLL clock
gen_clock(CLKGEN_MAIN, GCLK_GENCTRL_SRC_DPLL96M);
}
// Initialize clocks from factory calibrated internal clock
static void
clock_init_internal(void)
{
// Configure DFLL48M clock in open loop mode
SYSCTRL->DFLLCTRL.reg = 0;
uint32_t coarse = GET_FUSE(FUSES_DFLL48M_COARSE_CAL);
uint32_t fine = GET_FUSE(FUSES_DFLL48M_FINE_CAL);
SYSCTRL->DFLLVAL.reg = (SYSCTRL_DFLLVAL_COARSE(coarse)
| SYSCTRL_DFLLVAL_FINE(fine));
if (CONFIG_USBSERIAL) {
// Enable USB clock recovery mode
uint32_t mul = DIV_ROUND_CLOSEST(FREQ_MAIN, 1000);
SYSCTRL->DFLLMUL.reg = (SYSCTRL_DFLLMUL_FSTEP(10)
| SYSCTRL_DFLLMUL_MUL(mul));
SYSCTRL->DFLLCTRL.reg = (SYSCTRL_DFLLCTRL_MODE | SYSCTRL_DFLLCTRL_USBCRM
| SYSCTRL_DFLLCTRL_CCDIS
| SYSCTRL_DFLLCTRL_ENABLE);
} else {
SYSCTRL->DFLLCTRL.reg = SYSCTRL_DFLLCTRL_ENABLE;
}
while (!(SYSCTRL->PCLKSR.reg & SYSCTRL_PCLKSR_DFLLRDY))
;
// Switch main clock to DFLL48M clock
gen_clock(CLKGEN_MAIN, GCLK_GENCTRL_SRC_DFLL48M);
}
void
SystemInit(void)
{
@ -60,30 +113,9 @@ SystemInit(void)
while (GCLK->CTRL.reg & GCLK_CTRL_SWRST)
;
// Enable external 32Khz crystal and route to CLKGEN_32K
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))
;
gen_clock(CLKGEN_32K, GCLK_GENCTRL_SRC_XOSC32K);
// Configure DFLL48M clock (with CLKGEN_32K as reference)
route_pclock(SYSCTRL_GCLK_ID_DFLL48, CLKGEN_32K);
SYSCTRL->DFLLCTRL.reg = 0;
uint32_t mul = DIV_ROUND_CLOSEST(FREQ_MAIN, FREQ_32K);
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
gen_clock(CLKGEN_MAIN, GCLK_GENCTRL_SRC_DFLL48M | GCLK_GENCTRL_IDC);
// Init clocks
if (CONFIG_CLOCK_REF_X32K)
clock_init_32k();
else
clock_init_internal();
}