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[CM3] Systick Add helper function to easily set the desired frequency

This commit is contained in:
Frantisek Burian 2013-09-11 06:05:48 -07:00 committed by Piotr Esden-Tempski
parent 52758bb8fd
commit d541c14110
2 changed files with 37 additions and 2 deletions
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8
include/libopencm3/cm3/systick.h
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@ -85,8 +85,11 @@
#define STK_CSR_CLKSOURCE_EXT (0 << STK_CSR_CLKSOURCE_LSB)
#define STK_CSR_CLKSOURCE_AHB (1 << STK_CSR_CLKSOURCE_LSB)
#else
#define STK_CTRL_CLKSOURCE_AHB_DIV8 (0 << STK_CTRL_CLKSOURCE_LSB)
#define STK_CTRL_CLKSOURCE_AHB (1 << STK_CTRL_CLKSOURCE_LSB)
#define STK_CTRL_CLKSOURCE_AHB_DIV8 (0 << STK_CSR_CLKSOURCE_LSB)
#define STK_CTRL_CLKSOURCE_AHB (1 << STK_CSR_CLKSOURCE_LSB)
#define STK_CSR_CLKSOURCE_AHB_DIV8 (0 << STK_CSR_CLKSOURCE_LSB)
#define STK_CSR_CLKSOURCE_AHB (1 << STK_CSR_CLKSOURCE_LSB)
#endif
/**@}*/
@ -123,6 +126,7 @@
BEGIN_DECLS
void systick_set_reload(uint32_t value);
bool systick_set_frequency(uint32_t freq, uint32_t ahb);
uint32_t systick_get_reload(void);
uint32_t systick_get_value(void);
void systick_set_clocksource(uint8_t clocksource);

31
lib/cm3/systick.c
View File

@ -65,6 +65,37 @@ uint32_t systick_get_reload(void)
return STK_RVR & STK_RVR_RELOAD;
}
/** @brief SysTick Set clock and frequency of overflow
*
* This function sets the systick to AHB clock source, and the prescaler to
* generate interrupts with the desired frequency. The function fails, if
* the frequency is too low.
*
* @param[in] freq uint32_t The desired frequency in Hz
* @param[in] ahb uint32_t The current AHB frequency in Hz
* @returns true, if success, false if the desired frequency cannot be set.
*/
bool systick_set_frequency(uint32_t freq, uint32_t ahb)
{
uint32_t ratio = ahb / freq;
#if defined(__ARM_ARCH_6M__)
systick_set_clocksource(STK_CSR_CLKSOURCE_AHB);
#else
if (ratio >= (STK_RVR_RELOAD * 8)) {
/* This frequency is too slow */
return false;
} else if (ratio >= STK_RVR_RELOAD) {
ratio /= 8;
systick_set_clocksource(STK_CSR_CLKSOURCE_AHB_DIV8);
} else {
systick_set_clocksource(STK_CSR_CLKSOURCE_AHB);
}
#endif
systick_set_reload(ratio - 1);
return true;
}
/*---------------------------------------------------------------------------*/
/** @brief Get the current SysTick counter value.
*