How can I create 1.7MHz, 2.5MHz, 3MHz duty-cycle 50% by PWM in nRF52832

[chianglin]

Hi,

As well know, nRF52832 can use "16Mhz base-clock to output PWM signal, and it is very simple to create 4Mhz, 2Mhz, 1MHz signal output,

But, If I want to output a 1.7Mhz, 2.5Mhz, 3Mhz signal output with 50% duty-cycle, does it possible?

How can I do this job?

Thank you,

Chianglin

[haakonsh]

The 16MHz clock can be divided by 2^x, but this is just the base clock frequency, it's the COUNTERTOP register that determines the PWM frequency and  COMPx  (Compare Match) that determines the duty-cycle. 

See PWM — Pulse width modulation, PWM driver doc,  PWM driver API, and the PWM Driver Example. 

[chianglin]

Hi haakonsh,

Thank you for your answer so quickly.

So, it is possible to create any frequency output by PWM (Include 1.7MHz, 2.5MHz and 3MHz by 50% duty-cycle,)? And I only need to modify COUNTERTOP register?

Does it true?

Thank you

Chianglin

[haakonsh]

COUNTERTOP sets the PWM frequency, and nrf_pwm_sequence_t "sequence" of duty cycle values sets the duty-cycle. 

COUNTERTOP resets the PWM counter, the compare matches in the "sequence" triggers the GPIO state change.

See nrfx_pwm_simple_playback.

[chianglin]

Hi,

Please find the following source code.

static uint16_t const              m_demo1_top  = 6;
static uint16_t const              m_demo1_step = 200;

static uint8_t                     m_demo1_phase;
static nrf_pwm_values_individual_t m_demo1_seq_values;

static nrf_pwm_sequence_t const    m_demo1_seq =
{
    .values.p_individual = &m_demo1_seq_values,
    .length              = NRF_PWM_VALUES_LENGTH(m_demo1_seq_values),
    .repeats             = 0,
    .end_delay           = 2
};

static void demo1_handler(nrf_drv_pwm_evt_type_t event_type)
{
    if (event_type == NRF_DRV_PWM_EVT_FINISHED)
    {
	}
}

void PwmInit(void)
{
    nrf_drv_pwm_config_t const config0 =
    {
        .output_pins =
        {																// 設定 "連接到 PWM 的 Pin" 和 Pin 的初始狀態
            3 | NRF_DRV_PWM_PIN_INVERTED,								// Offset 0x00000560. Channel-0
            4 | NRF_DRV_PWM_PIN_INVERTED,								// Offset 0x00000564. Channel-1
            31 | NRF_DRV_PWM_PIN_INVERTED,								// Offset 0x00000569. Channel-2
            2 | NRF_DRV_PWM_PIN_INVERTED 								// Offset 0x0000056C. Channel-3
        },
        .irq_priority = APP_IRQ_PRIORITY_LOWEST,
        .base_clock   = NRF_PWM_CLK_16MHz,								// Offset 0x0000050C. 這個地方設的是 PWM 暫存器的 PRESCALER
        .count_mode   = /*NRF_PWM_MODE_UP_AND_DOWN*/ NRF_PWM_MODE_UP,	// Offset 0x00000504. 計數模式 (上緣 or 上緣+下緣)
        .top_value    = m_demo1_top,									// Offset 0x00000508. 脈衝發生器計數器計數的值。 當DECODER.MODE = WaveForm時，將忽略該寄存器，並且僅使用來自RAM的值。
        .load_mode    = NRF_PWM_LOAD_INDIVIDUAL,						// Offset 0x00000510. (bit-0/1) 1st half word (16-bit) in ch.0; 2nd in ch.1; ...; 4th in ch.3
        .step_mode    = NRF_PWM_STEP_AUTO								// Offset 0x00000510. (bit-8) 選擇用於推進活動序列的源: SEQ [n] .REFRESH用於確定加載內部比較寄存器
    };
    APP_ERROR_CHECK(nrf_drv_pwm_init(&m_pwm0, &config0, demo1_handler));

    m_demo1_seq_values.channel_0 = 3;
    m_demo1_seq_values.channel_1 = m_demo1_top/2 /*0*/;
    m_demo1_seq_values.channel_2 = m_demo1_top/2 /*0*/;
    m_demo1_seq_values.channel_3 = m_demo1_top/2 /*0*/;
    m_demo1_phase                = 0;

    (void)nrf_drv_pwm_simple_playback(&m_pwm0, &m_demo1_seq, 1, NRF_DRV_PWM_FLAG_LOOP);
}

If I call "PwmInit()" function. The PWM frequency is 2.667MHz and duty is 0.2us/0.16us.

How to modify PWM setting, then I can get 2.5MHz frequency and 50% duty-cycle?

Thank you,.

Chianglin

[haakonsh]

Oh, I've made a terrible mistake. You won't be able able to get a PWM frequency of 1.7MHz or 2.5MHz, from a 16MHz timer. You will only be able to have a PWM frequency in integers of MHz, ie, 1, 2, 3, 4... MHz. I'm sorry for the confusion. 

[chianglin]

Thank you for your information.