Look like a bug inside the function nrfx_saadc_calibrate_offset() in SDK 15.3.0 (nRF5_SDK_15.3.0_59ac345)

Question

m_cb.adc_state is set to NRF_SAADC_STATE_CALIBRATION inside the function nrfx_saadc_calibrate_offset(), but the value is never changed to NRF_SAADC_STATE_IDLE, even is the function return with NRFX_SUCCESS. 
 Many functions, like nrfx_saadc_channel_init() will return with NRFX_ERROR_BUSY as m_cb . adc_state != NRF_SAADC_STATE_IDLE. 
 Workaround is to call nrfx_saadc_uninit() that set m_cb . adc_state = NRF_SAADC_STATE_IDLE, and doing a new call to nrfx_saadc_init()

Daniel Landry · Answer

Hi Simon, 
 With some search, I found the solution from https://devzone.nordicsemi.com/f/nordic-q-a/33785/a-plurality-of-a-d-conversion-processing/129869#129869 
 
 The application must wait long enough to run the IRQ. nrfx_saadc_irq_handler () sets m_cb.adc_state = NRF_SAADC_STATE_IDLE and calls our own adc_event_handler. 
 
 I provide my solution in case it could help someone else. In my application, nrfx_saadc_calibrate_offset() is called once every 30 minutes. nrfx_saadc_uninit() and nrfx_saadc_init() are called in sequence as workaround for the errata 86 https://infocenter.nordicsemi.com/index.jsp?topic=%2Ferrata_nRF52832_Rev2%2FERR%2FnRF52832%2FRev2%2Flatest%2Fanomaly_832_86.html&cp=3_1_1_0_1_23

nrfx_saadc_config_t saadcCfg;

saadcCfg . resolution = NRF_SAADC_RESOLUTION_10BIT; 
 saadcCfg . oversample = NRF_SAADC_OVERSAMPLE_DISABLED; 
 saadcCfg . low_power_mode = false ; 
 saadcCfg.interrupt_priority = SAADC_IRQn; 
 nrfx_saadc_init ( & saadcCfg, ub_adc_event_handler);

/*-<ADC offset calibration >-*/ err_code = nrfx_saadc_calibrate_offset(); APP_ERROR_CHECK(err_code); 
 
 while ( nrfx_saadc_is_busy ()) // Wait for calibration to complete 
 { 
 __WFE (); // 
 __SEV (); // 
 __WFE (); // This sequence puts the system to sleep (SystemON) while waiting 
 } 
 // Nordic errata 86 workaround 
 nrfx_saadc_uninit (); 
 nrfx_saadc_init(&saadcCfg, ub_adc_event_handler);

power_vcc = power_vcc_read ();

printf ( "Vcc: %3d V 
 " , ( int )((power_vcc + 0.005 ) * 100 ));

/*****************************************************************************/ 
 
 /** 
 * \brief Read the Vcc voltage 
 * 
 * \param: none 
 * eturn Vcc 
 * 
 
 */ 
 float power_vcc_read ( void ) 
 { 
 nrf_saadc_channel_config_t channelcfg; 
 float volt; 
 nrf_saadc_value_t ADC_count; 
 
 // Channel configuration 
 channelcfg . resistor_p = NRF_SAADC_RESISTOR_DISABLED; 
 channelcfg . resistor_n = NRF_SAADC_RESISTOR_DISABLED; 
 channelcfg . gain = NRF_SAADC_GAIN1_6; 
 channelcfg . reference = NRF_SAADC_REFERENCE_INTERNAL; 
 channelcfg . acq_time = SAADC_CH_CONFIG_TACQ_20us; 
 channelcfg . mode = NRF_SAADC_MODE_SINGLE_ENDED; 
 /* Burst mode used for oversampling */ 
 if (NRFX_SAADC_CONFIG_OVERSAMPLE != 0 ) 
 { 
 channelcfg . burst = NRF_SAADC_BURST_ENABLED; 
 } 
 else 
 { 
 channelcfg . burst = NRF_SAADC_BURST_DISABLED; 
 } 
 channelcfg . pin_p = (SUPPLY_VCC_ADC_PIN + 1 ); /* NRF_SAADC_INPUT_DISABLED is the value 0 */ 
 channelcfg . pin_n = NRF_SAADC_INPUT_DISABLED; 
 nrfx_saadc_channel_init ( 0 , & channelcfg); 
 
 // ADC conversion 
 nrfx_saadc_sample_convert (SUPPLY_VCC_ADC_PIN, & ADC_count); 
 /* 3.6 = Internal Reference (0.6V) * 6 */ 
 volt = 3.6 * ADC_count / cfg . adcmax ; 
 
 return ( volt); 
 } 
 
 Best regards, 
 Daniel

Look like a bug inside the function nrfx_saadc_calibrate_offset() in SDK 15.3.0 (nRF5_SDK_15.3.0_59ac345)

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