ADC Infuriating Behaviour With Multi-channel Scan Using PPI to RTC

[snoopy20]

Been on all day at this and ready to smash something! :)

I need to do three 'steps' or 'tasks' which are:

1. read 5 channels
2. read 3 channels, which are the same as above minus two (there's a pin aux)
3. read 2 channels repeatedly filling up one of two banks with additional looping.

For brevity I've removed (3) to just do a single read and then call (1).

Each step works from adc interrupt. In the case of (1) and (2) the SAMPLE is wired to STARTED by PPI. Primarily this is because the RTC tick at 32KHz) is too fast.

Then this PPI is disabled and the RTC TICK EVENT is wired to STARTED instead. This gives 30.5us, and the 2 channels plus overhead are well within it.

Behaviour

The routine(s) loop twice and then end with no further interrupts. I believe the ADC is stuck on (2) because the TICK EVENT isn't being pumped through when the PPI channel is re-enabled.

I think I've tried everything to get this working but maybe another pair of eyes could help! 

extern struct statusProto status;

#define ADC_RESOLUTION SAADC_RESOLUTION_VAL_12bit
#define ADC_SAMPLETIME_CFG_SLOW SAADC_CH_CONFIG_TACQ_40us
#define ADC_SAMPLETIME_CFG_MPPT_VOLTAGE SAADC_CH_CONFIG_TACQ_10us
#define ADC_SAMPLETIME_CFG_MPPT_CURRENT SAADC_CH_CONFIG_TACQ_10us

// ADC takes 2us per channel, 4us + 15us + 5us = 24us

// 32,768Hz = 30.52us
// 667 (fit into ram)*30 = 20ms
#define MPPT_SAMPLES 1

// 200ms total / 20ms
#define MPPT_LOOP 2

enum {
  ADC_CH_USB,
  ADC_CH_FRONT,
  ADC_CH_REAR,
  ADC_CH_STORE,
  ADC_CH_LIGHTSENSE,
  ADC_CH_MPPT_VOLTAGE,
  ADC_CH_MPPT_CURRENT
};

struct mpptReadProto {
  int16_t voltage;
  int16_t current;
};

struct {
  volatile struct {
    int16_t usb;
    int16_t front;
    int16_t rear;
    int16_t storage;
    int16_t lightsense;
  } voltages;
  volatile struct {
    int16_t usb;
    int16_t front;
    int16_t rear;
  } currents;
  struct mpptReadProto banks[2][MPPT_SAMPLES];
} reads;

static void step3n (void);
static void step3 (void);
static void step2 (void);
static void step1 (void);

static void (*step)(void);
static uint8_t loop;
static struct mpptTrackProto track;
static struct mpptReadProto *currentBank;

static void step1 (void) {

  step = &step2;

  NRF_PPI->CHENSET = 1 << CFG_PPI_ADC_SAMPLEONSTART;

  NRF_GPIO->OUTCLR = 1 << CFG_PIN_ADC_MUX;

  NRF_SAADC->CH[ADC_CH_USB].PSELP = CFG_ADC_USB_PSEL;
  NRF_SAADC->CH[ADC_CH_FRONT].PSELP = CFG_ADC_FRONT_PSEL;
  NRF_SAADC->CH[ADC_CH_REAR].PSELP = CFG_ADC_REAR_PSEL;
  NRF_SAADC->CH[ADC_CH_STORE].PSELP = CFG_ADC_STORE_PSEL;
  NRF_SAADC->CH[ADC_CH_LIGHTSENSE].PSELP = CFG_ADC_LIGHTSENSE_PSEL;
  NRF_SAADC->RESULT.PTR = (uint32_t) &reads.voltages;
  NRF_SAADC->RESULT.MAXCNT = sizeof(reads.voltages) / 2;
  NRF_SAADC->TASKS_START = SAADC_TASKS_START_TASKS_START_Trigger << SAADC_TASKS_START_TASKS_START_Pos; 
}

static void step2 (void) {

  step = &step3;

  NRF_GPIO->OUTSET = 1 << CFG_PIN_ADC_MUX;
  // rather than wait for adc task compute we do here and send as event
  // this is only benefical if the storage read is greater than 500ms (adc task)
  if (reads.voltages.storage < STORAGE_VOLTAGE_CRITICAL_ON) {
    POWERMANAGER_EventStorageCritical();
  }

  NRF_SAADC->CH[ADC_CH_STORE].PSELP = SAADC_CH_PSELP_PSELP_NC;
  NRF_SAADC->CH[ADC_CH_LIGHTSENSE].PSELP = SAADC_CH_PSELP_PSELP_NC;
  NRF_SAADC->RESULT.PTR = (uint32_t) &reads.currents;
  NRF_SAADC->RESULT.MAXCNT = sizeof(reads.currents) / 2;
  NRF_SAADC->TASKS_START = SAADC_TASKS_START_TASKS_START_Trigger << SAADC_TASKS_START_TASKS_START_Pos; 
}

static void step3 (void) {

  currentBank = &reads.banks[0][0];
  step = &step3n;

  NRF_PPI->CHENCLR = 1 << CFG_PPI_ADC_SAMPLEONSTART;

  NRF_SAADC->CH[ADC_CH_USB].PSELP = SAADC_CH_PSELP_PSELP_NC;
  NRF_SAADC->CH[ADC_CH_FRONT].PSELP = SAADC_CH_PSELP_PSELP_NC;
  NRF_SAADC->CH[ADC_CH_REAR].PSELP = SAADC_CH_PSELP_PSELP_NC;
  NRF_SAADC->CH[ADC_CH_MPPT_VOLTAGE].PSELP = CFG_ADC_MPPT_VOLTAGE_PSEL;
  NRF_SAADC->CH[ADC_CH_MPPT_CURRENT].PSELP = CFG_ADC_MPPT_CURRENT_PSEL;
  NRF_SAADC->RESULT.PTR = (uint32_t) &reads.banks[0];
  NRF_SAADC->RESULT.MAXCNT = sizeof(reads.banks[0]) / sizeof(reads.banks[0][0]);
  NRF_SAADC->TASKS_START = SAADC_TASKS_START_TASKS_START_Trigger << SAADC_TASKS_START_TASKS_START_Pos;
  NRF_PPI->CHENSET = 1 << CFG_PPI_ADC_SAMPLEBYTIMER;
}


static void step3n (void) {

  // code cut down to remove looping
  NRF_SAADC->CH[ADC_CH_MPPT_VOLTAGE].PSELP = SAADC_CH_PSELP_PSELP_NC;
  NRF_SAADC->CH[ADC_CH_MPPT_CURRENT].PSELP = SAADC_CH_PSELP_PSELP_NC;
  NRF_PPI->CHENCLR = 1 << CFG_PPI_ADC_SAMPLEBYTIMER;
  step1();
}

void SAADC_IRQHandler (void) {

  NRF_SAADC->EVENTS_END = SAADC_EVENTS_END_EVENTS_END_NotGenerated << SAADC_EVENTS_END_EVENTS_END_Pos;
  step();
}

uint32_t ADC_TaskCalibrate (void) {

  NRF_SAADC->ENABLE = SAADC_ENABLE_ENABLE_Enabled << SAADC_ENABLE_ENABLE_Pos;
  NRF_SAADC->TASKS_CALIBRATEOFFSET = SAADC_TASKS_CALIBRATEOFFSET_TASKS_CALIBRATEOFFSET_Trigger << SAADC_TASKS_CALIBRATEOFFSET_TASKS_CALIBRATEOFFSET_Pos;
  return CFG_SCHEDULER_TIMER_MINIMUM;
}

uint32_t ADC_TaskStart (void) {

  NRF_SAADC->EVENTS_END = SAADC_EVENTS_END_EVENTS_END_NotGenerated << SAADC_EVENTS_END_EVENTS_END_Pos;
  NRF_SAADC->INTENSET = SAADC_INTENSET_END_Enabled << SAADC_INTENSET_END_Pos;
  
  // Note RTC Event tick is enabled elsewhere!

  step1();
  return CFG_SCHEDULER_TIMER_MINIMUM;
}


inline void ADC_Init (void) {

  NRF_GPIO->PIN_CNF[CFG_PIN_ADC_STORE] = pinDisconnectInputBuffer;
  NRF_GPIO->PIN_CNF[CFG_PIN_ADC_USB] = pinDisconnectInputBuffer;
  NRF_GPIO->PIN_CNF[CFG_PIN_ADC_FRONT] = pinDisconnectInputBuffer;
  NRF_GPIO->PIN_CNF[CFG_PIN_ADC_REAR] = pinDisconnectInputBuffer;
  NRF_GPIO->PIN_CNF[CFG_PIN_ADC_MPPT_VOLTAGE] = pinDisconnectInputBuffer;
  NRF_GPIO->PIN_CNF[CFG_PIN_ADC_MPPT_CURRENT] = pinDisconnectInputBuffer;
  NRF_GPIO->PIN_CNF[CFG_PIN_ADC_LIGHTSENSE] = pinDisconnectInputBuffer;
  NRF_GPIO->PIN_CNF[CFG_PIN_ADC_MUX] = pinDisconnectInputBuffer | (GPIO_PIN_CNF_DIR_Output << GPIO_PIN_CNF_DIR_Pos);
  NRF_GPIO->OUTSET = 1 << CFG_PIN_ADC_MUX;

  NRF_SAADC->RESOLUTION = SAADC_RESOLUTION_VAL_12bit << SAADC_RESOLUTION_VAL_Pos;
  NRF_SAADC->CH[ADC_CH_USB].CONFIG = SAADC_CH_CONFIG_REFSEL_Internal << SAADC_CH_CONFIG_REFSEL_Pos | SAADC_CH_CONFIG_GAIN_Gain1 << SAADC_CH_CONFIG_GAIN_Pos | ADC_SAMPLETIME_CFG_SLOW << SAADC_CH_CONFIG_TACQ_Pos;
  NRF_SAADC->CH[ADC_CH_FRONT].CONFIG = SAADC_CH_CONFIG_REFSEL_Internal << SAADC_CH_CONFIG_REFSEL_Pos | SAADC_CH_CONFIG_GAIN_Gain1 << SAADC_CH_CONFIG_GAIN_Pos | ADC_SAMPLETIME_CFG_SLOW << SAADC_CH_CONFIG_TACQ_Pos;
  NRF_SAADC->CH[ADC_CH_REAR].CONFIG = SAADC_CH_CONFIG_REFSEL_Internal << SAADC_CH_CONFIG_REFSEL_Pos | SAADC_CH_CONFIG_GAIN_Gain1 << SAADC_CH_CONFIG_GAIN_Pos | ADC_SAMPLETIME_CFG_SLOW << SAADC_CH_CONFIG_TACQ_Pos;
  NRF_SAADC->CH[ADC_CH_STORE].CONFIG = SAADC_CH_CONFIG_REFSEL_Internal << SAADC_CH_CONFIG_REFSEL_Pos | SAADC_CH_CONFIG_GAIN_Gain1_2 << SAADC_CH_CONFIG_GAIN_Pos | ADC_SAMPLETIME_CFG_SLOW << SAADC_CH_CONFIG_TACQ_Pos;
  NRF_SAADC->CH[ADC_CH_LIGHTSENSE].CONFIG = SAADC_CH_CONFIG_REFSEL_Internal << SAADC_CH_CONFIG_REFSEL_Pos | SAADC_CH_CONFIG_GAIN_Gain2 << SAADC_CH_CONFIG_GAIN_Pos | ADC_SAMPLETIME_CFG_SLOW << SAADC_CH_CONFIG_TACQ_Pos;
  NRF_SAADC->CH[ADC_CH_MPPT_VOLTAGE].CONFIG = SAADC_CH_CONFIG_REFSEL_Internal << SAADC_CH_CONFIG_REFSEL_Pos | SAADC_CH_CONFIG_GAIN_Gain1_6 << SAADC_CH_CONFIG_GAIN_Pos | ADC_SAMPLETIME_CFG_MPPT_VOLTAGE << SAADC_CH_CONFIG_TACQ_Pos;
  NRF_SAADC->CH[ADC_CH_MPPT_CURRENT].CONFIG = SAADC_CH_CONFIG_REFSEL_Internal << SAADC_CH_CONFIG_REFSEL_Pos | SAADC_CH_CONFIG_GAIN_Gain1_6 << SAADC_CH_CONFIG_GAIN_Pos | ADC_SAMPLETIME_CFG_MPPT_CURRENT << SAADC_CH_CONFIG_TACQ_Pos;
  
  NRF_PPI->CH[CFG_PPI_ADC_SAMPLEONSTART].EEP = (uint32_t) &NRF_SAADC->EVENTS_STARTED;
  NRF_PPI->CH[CFG_PPI_ADC_SAMPLEONSTART].TEP = (uint32_t) &NRF_SAADC->TASKS_SAMPLE;
  NRF_PPI->CH[CFG_PPI_ADC_SAMPLEBYTIMER].EEP = (uint32_t) &NRF_RTC1->EVENTS_TICK;
  NRF_PPI->CH[CFG_PPI_ADC_SAMPLEBYTIMER].TEP = (uint32_t) &NRF_SAADC->TASKS_SAMPLE;
  
  NVIC_SetPriority(SAADC_IRQn, CFG_INTERRUPT_PRIORITY_ADC);
  NVIC_EnableIRQ(SAADC_IRQn);
}

void ADC_Shutdown (void) {

  NRF_SAADC->ENABLE = SAADC_ENABLE_ENABLE_Disabled << SAADC_ENABLE_ENABLE_Pos;
}

[snoopy20]

Hi Karl,

I'm in production with it, it's working well.

I perform a number of steps in a adc-interrupt-loop with calibration being the first. Each step does a full reset of the adc using the errata code. It's not the fastest or the most optimal (i.e calibration every ~100ms) but it works and is fast enough!

A.

[Karl Ylvisaker]

Hello A,

I am glad to hear that it now functions as expected! :)
I understand that it is not ideal to have to go through the calibration so often, but unfortunately it is no way around the reset of the SAADC peripheral between the configurations you are using in this case.

Alternatively, if the repeated calibration is effecting the performance of other components in your system you could also run some tests on the feasibility for your application not to perform the offset calibration at all - as mentioned in the Product Specification the SAADC has a temperature dependent offset, but if what you are after in your application is the relative change in voltage over time, and the device is operating in a small temperature range - less than 10 degrees change in ambient temperature - it could also be feasible for you to run without the calibration. At least I do not know enough about your applications requirements and constraints to rule this possibility out.

Best regards,
Karl

[snoopy20]

It's not an issue in this application and to be honest if it were I'd monitor the internal temperature of the die and skip the step if the delta isn't high enough. There's always a way!

I do think however that some work is needed on the errata. For the 810 at least there are two around the calibration, which are the same thing, and as I've shown in this thread the errata applies at any time configuration changes between scans and not just calibration.

[Karl Ylvisaker]

snoopy20 said:

It's not an issue in this application and to be honest if it were I'd monitor the internal temperature of the die and skip the step if the delta isn't high enough. There's always a way!

Yeah, if it had been an issue for you we'd have to turn some rocks to see what the possible solutions could be, but I am glad to hear that this is not an issue! :) 

snoopy20 said:

I do think however that some work is needed on the errata. For the 810 at least there are two around the calibration, which are the same thing, and as I've shown in this thread the errata applies at any time configuration changes between scans and not just calibration.

To me it looks like you are seeing the effects of Errata 212 paired with the buffer-shift issue explained by my colleague Jørgen in the other thread, could you elaborate what you mean when you say 'the errata applies at any time configuration changes between scans and not just calibration?

I do agree that Errata 237 and Errata 252 perhaps should have been a single errata as I am not sure if their distinction is clear enough. I will check internally to see if what the background for this is.

Best regards,
Karl

[snoopy20]

There are three erratas for 810 adc at least:

1. when using calibration a sample may be taken, so one should configure the channels and dma after calibration.
2. when using calibration if a task_sample is invoked the reads will be garbage from that point forth. Really this is misconfiguration of running a timer and ppi event and not exactly errata per say.
3. when re-configuring adc registers (config,dma) after a multi-scan (not just one pass) then easydma will eventually buffer shift.

The errata says that a TASK_STOP should be used, this is not true as one of my posts above shows, however the delay it introduces may change the timing upon which easydma fails and perhaps gave the impression of such.

I actually use the 810 in another project where the adc is pushed to it's max computing real/apparent wattages for a generator. I don't have to reset there because I don't reconfigure the channels.

Also...

Another errata says that 5us channels can't be used with timer+PPI. This is untrue, I'm doing it and have never seen an issue.

And in the datasheet it says burst can't be combined with scan mode. This is not true, I do it just fine. But it may be the case that it can only be one sweep.

A.