Gd32f3x0 official PWM drive has a small positive bandwidth (inaccurate timing)

1. Code

#include "gd32f3x0.h"
#include <stdio.h>
#include "gd32f350r_eval.h"

void gpio_config(void);
void timer_config(void);

/*! \brief configure the GPIO ports \param[in] none \param[out] none \retval none */
void gpio_config(void)
{
    
    /*Configure PB3 PB10 PB11(TIMER1 CH1 CH2 CH3) as alternate function*/
    gpio_mode_set(GPIOB, GPIO_MODE_AF, GPIO_PUPD_NONE, GPIO_PIN_3);
    gpio_output_options_set(GPIOB, GPIO_OTYPE_PP, GPIO_OSPEED_50MHZ,GPIO_PIN_3);

    gpio_mode_set(GPIOB, GPIO_MODE_AF, GPIO_PUPD_NONE, GPIO_PIN_10);
    gpio_output_options_set(GPIOB, GPIO_OTYPE_PP, GPIO_OSPEED_50MHZ,GPIO_PIN_10);

    gpio_mode_set(GPIOB, GPIO_MODE_AF, GPIO_PUPD_NONE, GPIO_PIN_11);
    gpio_output_options_set(GPIOB, GPIO_OTYPE_PP, GPIO_OSPEED_50MHZ,GPIO_PIN_11);

    gpio_af_set(GPIOB, GPIO_AF_2, GPIO_PIN_3);
    gpio_af_set(GPIOB, GPIO_AF_2, GPIO_PIN_10);
    gpio_af_set(GPIOB, GPIO_AF_2, GPIO_PIN_11);
}

/*! \brief configure the TIMER peripheral \param[in] none \param[out] none \retval none */
void timer_config(void)
{
    
    /* ----------------------------------------------------------------------- TIMER1 configuration: generate 3 PWM signals with 3 different duty cycles: TIMER1CLK is 1MHz TIMER1 channel1 duty cycle = (4000/ 16000)* 100 = 25% TIMER1 channel2 duty cycle = (8000/ 16000)* 100 = 50% TIMER1 channel3 duty cycle = (12000/ 16000)* 100 = 75% ----------------------------------------------------------------------- */
    timer_oc_parameter_struct timer_ocintpara;
    timer_parameter_struct timer_initpara;

    rcu_periph_clock_enable(RCU_TIMER1);

    timer_deinit(TIMER1);

    /* TIMER1 configuration */
#ifdef GD32F330
    timer_initpara.prescaler         = 83;
#endif /* GD32F330 */
#ifdef GD32F350
    timer_initpara.prescaler         = 107;
#endif /* GD32F350 */
    timer_initpara.alignedmode       = TIMER_COUNTER_EDGE;
    timer_initpara.counterdirection  = TIMER_COUNTER_UP;
    timer_initpara.period            = 15999;
    timer_initpara.clockdivision     = TIMER_CKDIV_DIV1;
    timer_initpara.repetitioncounter = 0;
    timer_init(TIMER1,&timer_initpara);

    /* CH1,CH2 and CH3 configuration in PWM mode */
    timer_ocintpara.outputstate  = TIMER_CCX_ENABLE;
    timer_ocintpara.outputnstate = TIMER_CCXN_DISABLE;
    timer_ocintpara.ocpolarity   = TIMER_OC_POLARITY_HIGH;
    timer_ocintpara.ocnpolarity  = TIMER_OCN_POLARITY_HIGH;
    timer_ocintpara.ocidlestate  = TIMER_OC_IDLE_STATE_LOW;
    timer_ocintpara.ocnidlestate = TIMER_OCN_IDLE_STATE_LOW;

    timer_channel_output_config(TIMER1,TIMER_CH_1,&timer_ocintpara);
    timer_channel_output_config(TIMER1,TIMER_CH_2,&timer_ocintpara);
    timer_channel_output_config(TIMER1,TIMER_CH_3,&timer_ocintpara);

    timer_channel_output_pulse_value_config(TIMER1,TIMER_CH_1,3999);
    timer_channel_output_mode_config(TIMER1,TIMER_CH_1,TIMER_OC_MODE_PWM0);
    timer_channel_output_shadow_config(TIMER1,TIMER_CH_1,TIMER_OC_SHADOW_DISABLE);

    timer_channel_output_pulse_value_config(TIMER1,TIMER_CH_2,7999);
    timer_channel_output_mode_config(TIMER1,TIMER_CH_2,TIMER_OC_MODE_PWM0);
    timer_channel_output_shadow_config(TIMER1,TIMER_CH_2,TIMER_OC_SHADOW_DISABLE);

    timer_channel_output_pulse_value_config(TIMER1,TIMER_CH_3,11999);
    timer_channel_output_mode_config(TIMER1,TIMER_CH_3,TIMER_OC_MODE_PWM0);
    timer_channel_output_shadow_config(TIMER1,TIMER_CH_3,TIMER_OC_SHADOW_DISABLE);

    /* auto-reload preload enable */
    timer_auto_reload_shadow_enable(TIMER1);
    /* auto-reload preload enable */
    timer_enable(TIMER1);
}

/*! \brief main function \param[in] none \param[out] none \retval none */
int main(void)
{
    
    rcu_periph_clock_enable(RCU_GPIOB);
    gpio_config();
    timer_config();

    while (1);
}

2. analysis

PWM frequency =84MHz/(83+1)/（15999+1）= 62.5Hz

timer_channel_output_pulse_value_config(TIMER1,TIMER_CH_1,3999);

Calculate it like this TIMER1 channel1 duty cycle = (3999/ 16000)* 100 = 24.99375%.

So the correct answer is

timer_channel_output_pulse_value_config(TIMER1,TIMER_CH_1,4000);

TIMER1 channel1 duty cycle = (4000/ 16000)* 100 = 25%

stay PWM It is not easy to find this problem when the frequency is very low , stay 10~100kHz when , The problem that the positive bandwidth is too small can be obviously found by oscilloscope .