RE: Is it possible to use high drive mode with PWM?

Vidar Berg — Wed, 23 Feb 2022 09:12:59 GMT

Hi,

Yes, you can select high drive for the PWM outputs. The problem is that the PWM driver does not expose the drive strength as a configuration setting, so you either have to modify the driver code, or change the drive strength after the pwm has been enabled by nrf_drv_pwm_init().

Option 1: modify driver code

static void configure_pins(nrfx_pwm_t const * const p_instance,
                           nrfx_pwm_config_t const * p_config)
{
    uint32_t out_pins[NRF_PWM_CHANNEL_COUNT];
    uint8_t i;

    for (i = 0; i < NRF_PWM_CHANNEL_COUNT; ++i)
    {
        uint8_t output_pin = p_config->output_pins[i];
        if (output_pin != NRFX_PWM_PIN_NOT_USED)
        {
            bool inverted = output_pin &  NRFX_PWM_PIN_INVERTED;
            out_pins[i]   = output_pin & ~NRFX_PWM_PIN_INVERTED;

            if (inverted)
            {
                nrf_gpio_pin_set(out_pins[i]);
            }
            else
            {
                nrf_gpio_pin_clear(out_pins[i]);
            }

#if PWM_HIGH_DRIVE
            nrf_gpio_cfg(out_pins[i], NRF_GPIO_PIN_DIR_OUTPUT, NRF_GPIO_PIN_INPUT_DISCONNECT,
                NRF_GPIO_PIN_NOPULL, NRF_GPIO_PIN_H0H1, NRF_GPIO_PIN_NOSENSE);
#else 
            nrf_gpio_cfg_output(out_pins[i]);
#endif

        }
        else
        {
            out_pins[i] = NRF_PWM_PIN_NOT_CONNECTED;
        }
    }

    nrf_pwm_pins_set(p_instance->p_registers, out_pins);
}

Option 2: Change drive strength after nrf_drv_pwm_init()

    APP_ERROR_CHECK(nrf_drv_pwm_init());
   NRF_P0->PIN_CNF[< pin number on port 0 >] |= (GPIO_PIN_CNF_DRIVE_H0H1 << GPIO_PIN_CNF_DRIVE_Pos)

Best regards,

Vidar