sample ADC synced with PWM

[AmirZ]

Hi All,

I am newbie with nordic, and I need some help.

I am using nRF52832 with softdevice.

I need to generate a 128 kHz clock signal (PWM pulses with 128kHz frequency, duty cycle 50%,) and to sample Analog input at the same frequency (128 kHz) which is synced to the generated pulses (one sample to each cycle of the PWM output)

How can I do that? is there any example?

 

Regards,

Amir

[AmirZ]

Hi,

After reading some documentation and examples, I am trying to connect SAADC with PWM using PPI, but I failed to do that.

I manage to convert the PWM but faild to trigger the ADC sampling.

Attached my code to do this,

please give me some advises or suggestion to correct it.

void pwm_init(void)
{

uint32_t out_pins[] = {18, NRF_PWM_PIN_NOT_CONNECTED, NRF_PWM_PIN_NOT_CONNECTED, NRF_PWM_PIN_NOT_CONNECTED};
static uint16_t pwm_seq[2] = {62, 62};
nrf_pwm_sequence_t const seq =
{
.values.p_common = pwm_seq,
.length = sizeof(pwm_seq)/sizeof(uint16_t),
.repeats = 0,
.end_delay = 0
};

//nrf_gpio_cfg_output(5);
nrf_pwm_pins_set(NRF_PWM0, out_pins);
nrf_pwm_enable(NRF_PWM0);
nrf_pwm_configure(NRF_PWM0, NRF_PWM_CLK_16MHz, NRF_PWM_MODE_UP, 124);
nrf_pwm_loop_set(NRF_PWM0, 0);
nrf_pwm_decoder_set(NRF_PWM0, NRF_PWM_LOAD_COMMON, NRF_PWM_STEP_AUTO);

nrf_pwm_sequence_set(NRF_PWM0, 0, &seq);

NRF_PWM0->TASKS_SEQSTART[0] = 1;

}

void saadc_init(void)
{
ret_code_t err_code;
nrf_saadc_channel_config_t channel_config =
NRF_DRV_SAADC_DEFAULT_CHANNEL_CONFIG_SE(3);

err_code = nrf_drv_saadc_init(NULL, saadc_callback);
APP_ERROR_CHECK(err_code);

err_code = nrf_drv_saadc_channel_init(0, &channel_config);
APP_ERROR_CHECK(err_code);

err_code = nrf_drv_saadc_buffer_convert(m_buffer_pool[0], SAMPLES_IN_BUFFER);
APP_ERROR_CHECK(err_code);

/*err_code = nrf_drv_saadc_buffer_convert(m_buffer_pool[1], SAMPLES_IN_BUFFER);
APP_ERROR_CHECK(err_code);*/

}

void saadc_sampling_event_init(void)
{
ret_code_t err_code;

err_code = nrf_drv_ppi_init();
APP_ERROR_CHECK(err_code);


uint32_t pwm_pulse_event_addr = nrf_pwm_task_address_get(NRF_PWM0, NRF_PWM_EVENT_STOPPED );
uint32_t saadc_sample_task_addr = nrf_drv_saadc_sample_task_get();

#if 1
/* setup ppi channel so that timer compare event is triggering sample task in SAADC */
err_code = nrf_drv_ppi_channel_alloc(&m_ppi_channel);
APP_ERROR_CHECK(err_code);

err_code = nrf_drv_ppi_channel_assign(m_ppi_channel,
pwm_pulse_event_addr,
saadc_sample_task_addr);
APP_ERROR_CHECK(err_code);
#endif
}

void saadc_sampling_event_enable(void)
{
ret_code_t err_code = nrf_drv_ppi_channel_enable(m_ppi_channel);

APP_ERROR_CHECK(err_code);
}

void saadc_callback(nrf_drv_saadc_evt_t const * p_event)
{
if (p_event->type == NRF_DRV_SAADC_EVT_DONE)
{
ret_code_t err_code;

err_code = nrf_drv_saadc_buffer_convert(p_event->data.done.p_buffer, SAMPLES_IN_BUFFER);
APP_ERROR_CHECK(err_code);

int i;
printf("ADC event number: %d\r\n", (int)m_adc_evt_counter);

for (i = 0; i < SAMPLES_IN_BUFFER; i++)
{
printf("%d ", p_event->data.done.p_buffer[i]);
}

printf("\n\r");
}
}

void main()

{

pwm_init();
saadc_init();
saadc_sampling_event_init();

saadc_sampling_event_enable();

}