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cpu/atmega_common/periph/pwm: Minor fix & cleanup
- On pwm_poweron, the PWM resolution was not restored. (A custom resolution was
only usable if, PWM channel 0 is not used. That configuration is not common,
so this bug was likely never triggered)
- Disabled a work around to prevent flickering:
- Previously, PWM was disconnected on level 0% and 100%
- This increases the run time of `pwm_set()`
- It prevents using the PWM for wave form generation via DDS, as the wave
noticeably jumps when reaching 0% or 100%
- Slightly reduces memory requirements: 2 Bytes of RAM, 112 Bytes of ROM
- Tested with avr-gcc 9.2.0 and LTO enabled
This commit is contained in:
Marian Buschsieweke
parent
bf676d4728
commit
506288791d
@ -29,6 +29,8 @@
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#define WGM0 0
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#define WGM1 1
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#define WGM2 3
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#define COMB0 4
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#define COMB1 5
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#define COMA0 6
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#define COMA1 7
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@ -38,7 +40,7 @@ static struct {
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uint8_t res;
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} state[PWM_NUMOF];
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static inline unsigned get_prescaler(pwm_t dev, uint32_t *scale)
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static inline uint8_t get_prescaler(pwm_t dev, uint32_t *scale)
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{
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uint16_t divmask = pwm_conf[dev].div;
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uint32_t target = *scale;
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@ -58,8 +60,41 @@ static inline unsigned get_prescaler(pwm_t dev, uint32_t *scale)
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return pre;
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}
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static inline void compute_cra_and_crb(pwm_t dev, uint8_t pre)
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{
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uint8_t cra = (1 << WGM1) | (1 << WGM0);
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uint8_t crb = pre;
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if (pwm_conf[dev].pin_ch[0] != GPIO_UNDEF) {
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cra |= (1 << COMA1);
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}
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else {
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crb |= (1 << WGM2);
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}
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if (pwm_conf[dev].pin_ch[1] != GPIO_UNDEF) {
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cra |= (1 << COMB1);
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}
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state[dev].CRA = cra;
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state[dev].CRB = crb;
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}
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static inline void apply_config(pwm_t dev)
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{
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pwm_conf[dev].dev->CRA = state[dev].CRA;
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pwm_conf[dev].dev->CRB = state[dev].CRB;
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if (pwm_conf[dev].pin_ch[0] == GPIO_UNDEF) {
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/* If channel 0 is not used, variable resolutions can be used for
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* channel 1 */
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pwm_conf[dev].dev->OCR[0] = state[dev].res;
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}
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}
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uint32_t pwm_init(pwm_t dev, pwm_mode_t mode, uint32_t freq, uint16_t res)
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{
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(void)mode;
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/* only left implemented, max resolution 256 */
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assert(dev < PWM_NUMOF && mode == PWM_LEFT && res <= 256);
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/* resolution != 256 only valid if ch0 not used */
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@ -81,36 +116,25 @@ uint32_t pwm_init(pwm_t dev, pwm_mode_t mode, uint32_t freq, uint16_t res)
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/* find out prescaler */
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uint32_t scale = (CLOCK_CORECLOCK / (freq * (uint32_t)res));
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unsigned pre = get_prescaler(dev, &scale);
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uint8_t pre = get_prescaler(dev, &scale);
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freq = (CLOCK_CORECLOCK / (scale * (uint32_t)res));
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/* compute register values and enable pins */
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uint8_t cra = _BV(WGM1) | _BV(WGM0);
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uint8_t crb = 0;
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/* Compute configuration and store it in the state. (The state is needed
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* for later calls to pwm_poweron().)*/
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compute_cra_and_crb(dev, pre);
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state[dev].res = res - 1;
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res -= 1;
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/* configure pins and resolution. Output must be low at initialization.
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* Force the pin low to avoid flickering. */
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/* Apply configuration stored in state */
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apply_config(dev);
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/* Enable outputs */
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if (pwm_conf[dev].pin_ch[0] != GPIO_UNDEF) {
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gpio_init(pwm_conf[dev].pin_ch[0], GPIO_OUT);
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gpio_clear(pwm_conf[dev].pin_ch[0]);
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}
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else {
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crb |= _BV(WGM2);
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pwm_conf[dev].dev->OCR[0] = (uint8_t)res;
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}
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if (pwm_conf[dev].pin_ch[1] != GPIO_UNDEF) {
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gpio_init(pwm_conf[dev].pin_ch[1], GPIO_OUT);
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gpio_clear(pwm_conf[dev].pin_ch[1]);
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}
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pwm_conf[dev].dev->CRA = cra;
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pwm_conf[dev].dev->CRB = crb | (pre);
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state[dev].CRA = cra;
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state[dev].CRB = crb | (pre);
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state[dev].res = res;
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/* return real frequency */
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return freq;
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}
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@ -132,21 +156,11 @@ uint8_t pwm_channels(pwm_t dev)
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void pwm_set(pwm_t dev, uint8_t ch, uint16_t value)
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{
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assert(dev < PWM_NUMOF && ch <= 1 && pwm_conf[dev].pin_ch[ch] != GPIO_UNDEF);
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/* output flickers when duty cycle is 0 or 100%. Simply force the pin
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* low or high respectively to have a clean output. */
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uint8_t bit = (_BV(COMA1) >> (ch << 1));
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if (value >= state[dev].res) {
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pwm_conf[dev].dev->CRA &= ~bit;
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gpio_set(pwm_conf[dev].pin_ch[ch]);
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}
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else if (value == 0) {
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pwm_conf[dev].dev->CRA &= ~bit;
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gpio_clear(pwm_conf[dev].pin_ch[ch]);
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if (value > state[dev].res) {
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pwm_conf[dev].dev->OCR[ch] = state[dev].res;
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}
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else {
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pwm_conf[dev].dev->OCR[ch] = value;
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pwm_conf[dev].dev->CRA |= bit;
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}
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}
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@ -160,8 +174,8 @@ void pwm_poweron(pwm_t dev)
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else {
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power_timer0_enable();
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}
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pwm_conf[dev].dev->CRA = state[dev].CRA;
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pwm_conf[dev].dev->CRB = state[dev].CRB;
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apply_config(dev);
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}
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void pwm_poweroff(pwm_t dev)
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@ -169,7 +183,7 @@ void pwm_poweroff(pwm_t dev)
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assert(dev < PWM_NUMOF);
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pwm_conf[dev].dev->CRA = 0x00;
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pwm_conf[dev].dev->CRB = 0x00;
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/* disable power reduction */
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/* disable timers to lower power consumption */
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if (dev) {
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power_timer2_disable();
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}
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