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cc2538: Allow for configuration of processor speed

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This commit is contained in:
Ulf Knoblich 2015-05-12 14:06:40 +02:00
parent 730bda2001
commit d8efa8428c
7 changed files with 107 additions and 38 deletions
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35
cpu/cc2538/clock.c
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@ -37,12 +37,12 @@
* Implementation of the clock module for the cc2538
*
* To implement the clock functionality, we use the SysTick peripheral on the
* cortex-M3. We run the system clock at 16 MHz and we set the SysTick to give
* us 128 interrupts / sec. However, the Sleep Timer counter value is used for
* the number of elapsed ticks in order to avoid a significant time drift caused
* by PM1/2. Contrary to the Sleep Timer, the SysTick peripheral is indeed
* frozen during PM1/2, so adjusting upon wake-up a tick counter based on this
* peripheral would hardly be accurate.
* cortex-M3. We run the system clock at a configurable speed and set the
* SysTick to give us 128 interrupts / sec. However, the Sleep Timer counter
* value is used for the number of elapsed ticks in order to avoid a
* significant time drift caused by PM1/2. Contrary to the Sleep Timer, the
* SysTick peripheral is indeed frozen during PM1/2, so adjusting upon wake-up
* a tick counter based on this peripheral would hardly be accurate.
* @{
*
* \file
@ -62,7 +62,19 @@
#include <stdint.h>
/*---------------------------------------------------------------------------*/
#define RTIMER_CLOCK_TICK_RATIO (RTIMER_SECOND / CLOCK_SECOND)
#define RELOAD_VALUE (125000 - 1) /** Fire 128 times / sec */
/* Prescaler for GPT0:Timer A used for clock_delay_usec(). */
#if SYS_CTRL_SYS_CLOCK < SYS_CTRL_1MHZ
#error System clock speeds below 1MHz are not supported
#endif
#define PRESCALER_VALUE (SYS_CTRL_SYS_CLOCK / SYS_CTRL_1MHZ - 1)
/* Reload value for SysTick counter */
#if SYS_CTRL_SYS_CLOCK % CLOCK_SECOND
/* Too low clock speeds will lead to reduced accurracy */
#error System clock speed too slow for CLOCK_SECOND, accuracy reduced
#endif
#define RELOAD_VALUE (SYS_CTRL_SYS_CLOCK / CLOCK_SECOND - 1)
static volatile uint64_t rt_ticks_startup = 0, rt_ticks_epoch = 0;
/*---------------------------------------------------------------------------*/
@ -74,8 +86,8 @@ static volatile uint64_t rt_ticks_startup = 0, rt_ticks_epoch = 0;
*
* We also initialise GPT0:Timer A, which is used by clock_delay_usec().
* We use 16-bit range (individual), count-down, one-shot, no interrupts.
* The system clock is at 16MHz giving us 62.5 nano sec ticks for Timer A.
* Prescaled by 16 gives us a very convenient 1 tick per usec
* The prescaler is computed according to the system clock in order to get 1
* tick per usec.
*/
void
clock_init(void)
@ -98,15 +110,14 @@ clock_init(void)
/* Make sure GPT0 is off */
REG(GPT_0_BASE + GPTIMER_CTL) = 0;
/* 16-bit */
REG(GPT_0_BASE + GPTIMER_CFG) = 0x04;
/* One-Shot, Count Down, No Interrupts */
REG(GPT_0_BASE + GPTIMER_TAMR) = GPTIMER_TAMR_TAMR_ONE_SHOT;
/* Prescale by 16 (thus, value 15 in TAPR) */
REG(GPT_0_BASE + GPTIMER_TAPR) = 0x0F;
/* Prescale depending on system clock used */
REG(GPT_0_BASE + GPTIMER_TAPR) = PRESCALER_VALUE;
}
/*---------------------------------------------------------------------------*/
CCIF clock_time_t