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fix 16bit timer pwm output #133

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Merged
merged 2 commits into from
Dec 19, 2013
Merged

fix 16bit timer pwm output #133

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a3465b5
fix 16bit timer pwm output
xiongyihui Dec 19, 2013
6501b16
Merge remote-tracking branch 'upstream/master'
xiongyihui Dec 19, 2013
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16 changes: 10 additions & 6 deletions libraries/mbed/targets/hal/TARGET_NXP/TARGET_LPC11UXX/pwmout_api.c
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Original file line number Diff line number Diff line change
Expand Up @@ -66,8 +66,6 @@ static LPC_CTxxBx_Type *Timers[4] = {
LPC_CT32B0, LPC_CT32B1
};

static unsigned int pwm_clock_mhz;

void pwmout_init(pwmout_t* obj, PinName pin) {
// determine the channel
PWMName pwm = (PWMName)pinmap_peripheral(pin, PinMap_PWM);
Expand All @@ -92,8 +90,6 @@ void pwmout_init(pwmout_t* obj, PinName pin) {
/* Reset Functionality on MR3 controlling the PWM period */
timer->MCR = 1 << 10;

pwm_clock_mhz = SystemCoreClock / 1000000;

// default to 20ms: standard for servos, and fine for e.g. brightness control
pwmout_period_ms(obj, 20);
pwmout_write (obj, 0);
Expand Down Expand Up @@ -141,11 +137,18 @@ void pwmout_period_ms(pwmout_t* obj, int ms) {
// Set the PWM period, keeping the duty cycle the same.
void pwmout_period_us(pwmout_t* obj, int us) {
int i = 0;
uint32_t period_ticks = pwm_clock_mhz * us;
uint32_t period_ticks = (uint32_t)(((uint64_t)SystemCoreClock * (uint64_t)us) / (uint64_t)1000000);

timer_mr tid = pwm_timer_map[obj->pwm];
LPC_CTxxBx_Type *timer = Timers[tid.timer];
uint32_t old_period_ticks = timer->MR3;

// for 16bit timer, set prescaler to avoid overflow
uint16_t high_period_ticks = period_ticks >> 16;
if ((high_period_ticks) && (timer == LPC_CT16B0 || timer == LPC_CT16B1)) {
timer->PR = high_period_ticks;
period_ticks /= (high_period_ticks + 1);
}

timer->TCR = TCR_RESET;
timer->MR3 = period_ticks;
Expand All @@ -169,13 +172,14 @@ void pwmout_pulsewidth_ms(pwmout_t* obj, int ms) {
}

void pwmout_pulsewidth_us(pwmout_t* obj, int us) {
uint32_t t_on = (uint32_t)(((uint64_t)SystemCoreClock * (uint64_t)us) / (uint64_t)1000000);
timer_mr tid = pwm_timer_map[obj->pwm];
LPC_CTxxBx_Type *timer = Timers[tid.timer];
uint32_t t_on = (uint32_t)(((uint64_t)SystemCoreClock * (uint64_t)us) / (uint64_t)1000000 / (timer->PR + 1));

timer->TCR = TCR_RESET;
if (t_on > timer->MR3) {
pwmout_period_us(obj, us);
t_on = (uint32_t)(((uint64_t)SystemCoreClock * (uint64_t)us) / (uint64_t)1000000 / (timer->PR + 1));
}
uint32_t t_off = timer->MR3 - t_on;
timer->MR[tid.mr] = t_off;
Expand Down