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samd/mcu: Set the SAMD21 us-counter to 2 MHz for better resolution. 

It turned out that the result of calling ticks_us() was always either odd
or even, depending on some internal state during boot.  So the us-counter
was set to a 2 MHz input and the result shifted by 1.  The counting period
is still long enough, since internally a (now) 63 bit value is used for us.
This commit is contained in:
robert-hh 2023-01-25 18:05:40 +01:00 committed by Damien George
parent 76cf98c35b
commit 4160ec087b
3 changed files with 4 additions and 8 deletions
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6
ports/samd/mcu/samd21/clock_config.c
View File

@ -166,7 +166,7 @@ void init_clocks(uint32_t cpu_freq) {
// GCLK0: 48MHz, source: DFLL48M or FDPLL96M, usage: CPU
// GCLK1: 32kHz, source: XOSC32K or OSCULP32K, usage: FDPLL96M reference
// GCLK2: 1-48MHz, source: DFLL48M, usage: Peripherals
// GCLK3: 1Mhz, source: DFLL48M, usage: us-counter (TC4/TC5)
// GCLK3: 2Mhz, source: DFLL48M, usage: us-counter (TC4/TC5)
// GCLK4: 32kHz, source: XOSC32K, if crystal present, usage: DFLL48M reference
// GCLK5: 48MHz, source: DFLL48M, usage: USB
// GCLK8: 1kHz, source: XOSC32K or OSCULP32K, usage: WDT and RTC
@ -291,8 +291,8 @@ void init_clocks(uint32_t cpu_freq) {
set_cpu_freq(cpu_freq);
// Enable GCLK output: 1MHz on GCLK3 for TC4
GCLK->GENDIV.reg = GCLK_GENDIV_ID(3) | GCLK_GENDIV_DIV(48);
// Enable GCLK output: 2MHz on GCLK3 for TC4
GCLK->GENDIV.reg = GCLK_GENDIV_ID(3) | GCLK_GENDIV_DIV(24);
GCLK->GENCTRL.reg = GCLK_GENCTRL_GENEN | GCLK_GENCTRL_SRC_DFLL48M | GCLK_GENCTRL_ID(3);
while (GCLK->STATUS.bit.SYNCBUSY) {
}

2
ports/samd/mphalport.c
View File

@ -147,7 +147,7 @@ uint64_t mp_hal_ticks_us_64(void) {
us64_upper++;
}
#if defined(MCU_SAMD21)
return ((uint64_t)us64_upper << 32) | us64_lower;
return ((uint64_t)us64_upper << 31) | (us64_lower >> 1);
#elif defined(MCU_SAMD51)
return ((uint64_t)us64_upper << 28) | (us64_lower >> 4);
#endif

4
ports/samd/mphalport.h
View File

@ -54,11 +54,7 @@ static inline mp_uint_t mp_hal_ticks_ms(void) {
}
static inline mp_uint_t mp_hal_ticks_us(void) {
#if defined(MCU_SAMD21)
return REG_TC4_COUNT32_COUNT;
#else
return (mp_uint_t)mp_hal_ticks_us_64();
#endif
}
#if defined(MCU_SAMD21)