nrf52832 PPI SAADC Oversample,sample rate up to 250hz

[Coder_hope]

I am using SAADC and PPI to sample 2 channels data with oversample,when I set  timer tick 5ms,the sample rate is 200hz and the system works well,now I want to improve the sample rete,So I change the timer tick to 2ms,the sample rate is 500hz.but I tested that the SAADC output data rate is up to 250hz, the timers frequency is 16M.

void ECG8233_saadc_sampling_event_init(void)
{
ret_code_t err_code;

err_code = nrf_drv_ppi_init();
APP_ERROR_CHECK(err_code);

nrf_drv_timer_config_t timer_cfg = NRF_DRV_TIMER_DEFAULT_CONFIG;
// timer_cfg.frequency = 
timer_cfg.bit_width =NRF_TIMER_BIT_WIDTH_32; 

err_code = nrf_drv_timer_init(&m_hardware_timer, &timer_cfg, timer_handler);//m_hardware_timer即TIMER1
APP_ERROR_CHECK(err_code);


uint32_t ticks = nrf_drv_timer_ms_to_ticks(&m_hardware_timer, 2); 

nrf_drv_timer_extended_compare(&m_hardware_timer,
NRF_TIMER_CC_CHANNEL0,
ticks,
NRF_TIMER_SHORT_COMPARE0_CLEAR_MASK,
false);

nrf_drv_timer_enable(&m_hardware_timer);

uint32_t timer_compare_event_addr = nrf_drv_timer_compare_event_address_get(&m_hardware_timer,
NRF_TIMER_CC_CHANNEL0);
uint32_t saadc_sample_task_addr = nrf_drv_saadc_sample_task_get();


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,
timer_compare_event_addr,
saadc_sample_task_addr);
APP_ERROR_CHECK(err_code);
}

can anyone help me to solve this problem ,is there any configuration wrong?

[haakonsh]

Can you share the rest of your SAADC-related code?

I suggest you enter a debug session and read the value of the BITMODE, PRESCALER, and CC[x] register. 

That will tell us whether the TIMER is triggering the SAADC's sample task when we expect it to. 

[Coder_hope]

void ECG8233_saadc_init(void)
{
	ret_code_t err_code;
	nrf_saadc_channel_config_t channel_ECG_config =
    NRF_DRV_SAADC_DEFAULT_CHANNEL_CONFIG_DIFFERENTIAL(ECG_8233_ADC_PIN_IN,ECG_8233_ADC_REF_PIN_IN);
	channel_ECG_config.gain = NRF_SAADC_GAIN1_4;
	channel_ECG_config.burst = NRF_SAADC_BURST_ENABLED;

    nrf_saadc_channel_config_t channel_VBAT_config =
            NRF_DRV_SAADC_DEFAULT_CHANNEL_CONFIG_SE(BAT_VOL_ADC_PIN_IN);
	channel_VBAT_config.burst = NRF_SAADC_BURST_ENABLED;	

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

    err_code = nrf_drv_saadc_channel_init(0, &channel_ECG_config);
    APP_ERROR_CHECK(err_code);
	//ADC  BatteryLevel config
	nrf_delay_ms(10);
    err_code = nrf_drv_saadc_channel_init(1, &channel_VBAT_config);
    APP_ERROR_CHECK(err_code);

	err_code = nrf_drv_saadc_buffer_convert(m_buffer_pool, SAMPLES_IN_BUFFER);
    APP_ERROR_CHECK(err_code);
}

this is the rest  of SAADC related code,ECG signal  and battery voltage, this is saadc config

// <0=> 8 bit 
// <1=> 10 bit 
// <2=> 12 bit 
// <3=> 14 bit 

#ifndef NRFX_SAADC_CONFIG_RESOLUTION
#define NRFX_SAADC_CONFIG_RESOLUTION 3  //1:10bit
#endif

// <o> NRFX_SAADC_CONFIG_OVERSAMPLE  - Sample period
 
// <0=> Disabled 
// <1=> 2x 
// <2=> 4x 
// <3=> 8x 
// <4=> 16x 
// <5=> 32x 
// <6=> 64x 
// <7=> 128x 
// <8=> 256x 

#ifndef NRFX_SAADC_CONFIG_OVERSAMPLE
#define NRFX_SAADC_CONFIG_OVERSAMPLE 8//8
#endif

[haakonsh]

When debugging peripherals you need to read the content of the peripheral's Registers and compare them with what you'd expect them to be according to their documentation. 

In your case you're missing a part the SAADC configuration and this would be easy to find from reading the OVERSAMPLE register as it will be 0x00000000 = No oversampling in your case. See nrfx_saadc_init and nrfx_saadc_config_t API docs.


Can you share the code that triggers the SAADC's start task?

[Coder_hope]

void ECG8233_saadc_sampling_event_enable(void)
{
    ret_code_t err_code = nrf_drv_ppi_channel_enable(m_ppi_channel);

    APP_ERROR_CHECK(err_code);
}

I use this function to start SAADC sample after" ECG8233_saadc_sampling_event_init" ，

I have defined  NRFX_SAADC_CONFIG_OVERSAMPLE  = 8,,I checked  nrfx_saadc_config_t , the oversample is configed to 8 (256X)。

[haakonsh]

Coder_hope said:

I have defined  NRFX_SAADC_CONFIG_OVERSAMPLE  = 8

 aah the default configs, yes, that should be correct then. 

Can you read the TIMER registers after you've started it?