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Merge branch 'master' of https://github.com/mbedmicro/mbed

pull/1/head
samux 2013-03-21 13:37:36 +00:00
parent 301abc8fef 3fa0f0a3c0
commit 7ee1e59662
1 changed files with 5 additions and 35 deletions
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40
libraries/mbed/vendor/Freescale/capi/us_ticker.c vendored
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@ -32,26 +32,18 @@ void us_ticker_init(void) {
/****************************************************************************** /******************************************************************************
* Timer for us timing. * Timer for us timing.
*
* Need to have 32bit resolution, we are using the PIT (2x32bit timers) for
* that. All the other timers have only 16bit resolution.
* Unfortunately, the PIT does not have a prescaler, therefore it ticks at the
* bus clock of (24)MHz.
* To keep 32bit resolution we are chaining the 2 32bit timers together dividing
* the final result by 24.
* NOTE: The PIT is a countdown timer.
******************************************************************************/ ******************************************************************************/
static void pit_init(void) { static void pit_init(void) {
SIM->SCGC6 |= SIM_SCGC6_PIT_MASK; // Clock PIT SIM->SCGC6 |= SIM_SCGC6_PIT_MASK; // Clock PIT
PIT->MCR = 0; // Enable PIT PIT->MCR = 0; // Enable PIT
// Timer 1 // Channel 1
PIT->CHANNEL[1].LDVAL = 0xFFFFFFFF; PIT->CHANNEL[1].LDVAL = 0xFFFFFFFF;
PIT->CHANNEL[1].TCTRL = PIT_TCTRL_CHN_MASK; // Chain to timer 0, disable Interrupts PIT->CHANNEL[1].TCTRL = PIT_TCTRL_CHN_MASK; // Chain to timer 0, disable Interrupts
PIT->CHANNEL[1].TCTRL |= PIT_TCTRL_TEN_MASK; // Start timer 1 PIT->CHANNEL[1].TCTRL |= PIT_TCTRL_TEN_MASK; // Start timer 1
// Timer 2 // Use channel 0 as a prescaler for channel 1
PIT->CHANNEL[0].LDVAL = 0xFFFFFFFF; PIT->CHANNEL[0].LDVAL = 23;
PIT->CHANNEL[0].TCTRL = PIT_TCTRL_TEN_MASK; // Start timer 0, disable interrupts PIT->CHANNEL[0].TCTRL = PIT_TCTRL_TEN_MASK; // Start timer 0, disable interrupts
} }
@ -59,31 +51,9 @@ uint32_t us_ticker_read() {
if (!us_ticker_inited) if (!us_ticker_inited)
us_ticker_init(); us_ticker_init();
/* To use LTMR64H and LTMR64L, timer 0 and timer 1 need to be chained. // The PIT is a countdown timer
* To obtain the correct value, first read LTMR64H and then LTMR64L. return ~(PIT->CHANNEL[1].CVAL);
* LTMR64H will have the value of CVAL1 at the time of the first access,
* LTMR64L will have the value of CVAL0 at the time of the first access,
* therefore the application does not need to worry about carry-over effects
* of the running counter.
*/
uint64_t ticks;
ticks = (uint64_t)PIT->LTMR64H << 32;
ticks |= (uint64_t)PIT->LTMR64L;
// More efficient division by constant integer (24): /8 /3
// complement (because count down timer) and divide by 8
ticks = (~ticks) >> 3;
// divide by 3
if (ticks > 0xFFFFFFFF) {
ticks /= 3;
} else {
ticks = (ticks * 0x55555556) >> 32;
} }
return (uint32_t)(0xFFFFFFFF & ticks);
}
/****************************************************************************** /******************************************************************************
* Timer Event * Timer Event