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Fix a stupid off-by-one that prevented this code from working.

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Update to use 32-bit microsecond values.

Remove PIOS_DELAY_DiffuS per consensus (caller can do it easily themselves).

Update the core delay logic per Stac's suggestion to a version that is
resistant to various overflows.
This commit is contained in:
Mike Smith 2011-07-25 20:55:48 -07:00
parent 480f07a264
commit df5569c758
2 changed files with 28 additions and 27 deletions
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48
flight/PiOS/STM32F10x/pios_delay.c
View File

@ -37,7 +37,7 @@
/* these should be defined by CMSIS, but they aren't */ /* these should be defined by CMSIS, but they aren't */
#define DWT_CTRL (*(volatile uint32_t *)0xe0001000) #define DWT_CTRL (*(volatile uint32_t *)0xe0001000)
#define CYCCNTENA (1<<1) #define CYCCNTENA (1<<0)
#define DWT_CYCCNT (*(volatile uint32_t *)0xe0001004) #define DWT_CYCCNT (*(volatile uint32_t *)0xe0001004)
@ -57,6 +57,7 @@ int32_t PIOS_DELAY_Init(void)
/* compute the number of system clocks per microsecond */ /* compute the number of system clocks per microsecond */
RCC_GetClocksFreq(&clocks); RCC_GetClocksFreq(&clocks);
us_ticks = clocks.SYSCLK_Frequency / 1000000; us_ticks = clocks.SYSCLK_Frequency / 1000000;
PIOS_DEBUG_Assert(us_ticks > 1);
/* turn on access to the DWT registers */ /* turn on access to the DWT registers */
CoreDebug->DEMCR |= CoreDebug_DEMCR_TRCENA_Msk; CoreDebug->DEMCR |= CoreDebug_DEMCR_TRCENA_Msk;
@ -75,18 +76,32 @@ int32_t PIOS_DELAY_Init(void)
* // Wait for 500 uS * // Wait for 500 uS
* PIOS_DELAY_Wait_uS(500); * PIOS_DELAY_Wait_uS(500);
* \endcode * \endcode
* \param[in] uS delay (1..65535 microseconds) * \param[in] uS delay
* \return < 0 on errors * \return < 0 on errors
*/ */
int32_t PIOS_DELAY_WaituS(uint16_t uS) int32_t PIOS_DELAY_WaituS(uint32_t uS)
{ {
uint16_t deadline; uint32_t elapsed = 0;
uint32_t last_count = DWT_CYCCNT;
for (;;) {
uint32_t current_count = DWT_CYCCNT;
uint32_t elapsed_uS;
/* calculate the time at which we should stop waiting */ /* measure the time elapsed since the last time we checked */
deadline = PIOS_DELAY_GetuS() + uS; elapsed += current_count - last_count;
last_count = current_count;
/* and wait until that time has arrived */ /* convert to microseconds */
while (PIOS_DELAY_DiffuS(deadline) < 0) { elapsed_uS = elapsed / us_ticks;
if (elapsed_uS >= uS)
break;
/* reduce the delay by the elapsed time */
uS -= elapsed_uS;
/* keep fractional microseconds for the next iteration */
elapsed %= us_ticks;
} }
/* No error */ /* No error */
@ -104,7 +119,7 @@ int32_t PIOS_DELAY_WaituS(uint16_t uS)
* \param[in] mS delay (1..65535 milliseconds) * \param[in] mS delay (1..65535 milliseconds)
* \return < 0 on errors * \return < 0 on errors
*/ */
int32_t PIOS_DELAY_WaitmS(uint16_t mS) int32_t PIOS_DELAY_WaitmS(uint32_t mS)
{ {
while (mS--) { while (mS--) {
PIOS_DELAY_WaituS(1000); PIOS_DELAY_WaituS(1000);
@ -118,24 +133,11 @@ int32_t PIOS_DELAY_WaitmS(uint16_t mS)
* @brief Query the Delay timer for the current uS * @brief Query the Delay timer for the current uS
* @return A microsecond value * @return A microsecond value
*/ */
uint16_t PIOS_DELAY_GetuS() uint32_t PIOS_DELAY_GetuS()
{ {
return DWT_CYCCNT / us_ticks; return DWT_CYCCNT / us_ticks;
} }
/**
* @brief Compute the difference between now and a reference time
* @param[in] the reference time to compare now to
* @return The number of uS since the delay
*
* @note the user is responsible for worrying about rollover on the 16 bit uS counter
*/
int32_t PIOS_DELAY_DiffuS(uint16_t ref)
{
int32_t ret_t = ref;
return (int16_t) (PIOS_DELAY_GetuS() - ret_t);
}
#endif #endif
/** /**

7
flight/PiOS/inc/pios_delay.h
View File

@ -34,10 +34,9 @@
/* Public Functions */ /* Public Functions */
extern int32_t PIOS_DELAY_Init(void); extern int32_t PIOS_DELAY_Init(void);
extern int32_t PIOS_DELAY_WaituS(uint16_t uS); extern int32_t PIOS_DELAY_WaituS(uint32_t uS);
extern int32_t PIOS_DELAY_WaitmS(uint16_t mS); extern int32_t PIOS_DELAY_WaitmS(uint32_t mS);
extern uint16_t PIOS_DELAY_GetuS(); extern uint32_t PIOS_DELAY_GetuS();
extern int32_t PIOS_DELAY_DiffuS(uint16_t ref);
#endif /* PIOS_DELAY_H */ #endif /* PIOS_DELAY_H */