52820 COMP interrupt problem

[logan.xu]

Hi, Friend, 

      I have a light sensor connected to P0.04/AIN2 on 52820, and use COMP to detect the change of voltage. 

      Here is my test code. When light change, the return value of nrfx_comp_sample() is correct (it can change between 0 and 1). 

      But if I channge the params of nrf_drv_comp_start(0, 0) to nrf_drv_comp_start(NRF_DRV_COMP_EVT_EN_DOWN_MASK | NRF_DRV_COMP_EVT_EN_UP_MASK, 0),  the RTT Viewer will printf sample value every 0.5s, but stoped (printing nothing) when AIN2 vlotage changed.  

      I suppose is the interrupt problem. What can I do next? Thank you.

void comp_event_handler(nrf_comp_event_t evt)
{
        NRF_LOG_INFO("VAL=%",evt);
}

void COMP_TEST()
{
        uint32_t err_code;
        nrf_drv_comp_config_t comp_config = NRF_DRV_COMP_DEFAULT_CONFIG(NRF_COMP_INPUT_2);

        comp_config.reference = 4; // <0=> Internal 1.2V, <1=> Internal 1.8V, <2=> Internal 2.4V, <4=> VDD, <7=> ARef
        comp_config.ext_ref = NRF_COMP_EXT_REF_0; // Use AIN0 as external analog reference.
        comp_config.main_mode = 0; /* // <0=> Single ended, <1=> Differential */
        comp_config.threshold.th_down = NRFX_VOLTAGE_THRESHOLD_TO_INT(1.0, 3.3);
        comp_config.threshold.th_up = NRFX_VOLTAGE_THRESHOLD_TO_INT(2.0, 3.3);
        comp_config.speed_mode = 2; // <0=> Low power, <1=> Normal, <2=> High speed
        comp_config.hyst = 0; // <0=> No, <1=> 50mV
        comp_config.interrupt_priority = 6;

        NRF_LOG_INFO("#####%d,%d,%d,%d,%d", comp_config.input, comp_config.reference, comp_config.threshold.th_down,
        comp_config.threshold.th_up, comp_config.interrupt_priority);
        err_code = nrf_drv_comp_init(&comp_config, comp_event_handler);
        nrf_drv_comp_start(0, 0);

        while (true)
        {
                NRF_LOG_INFO("VAL:%d", nrfx_comp_sample());
                NRF_LOG_FLUSH();
                nrf_delay_ms(500);
        }
}

[Jørgen Holmefjord]

Hi,

See my comment about PRS here. As far as I can see, the nrfx_prs_acquire() function should get a NULL-pointer returned from prs_box_get(), which should skip the if-setting and return success. 

I tested your code (with some small modifications, replaced NRF_LOG with LED blinking, and connected a button as input, as I do not have a light sensor). I was able to generate interrupts (checked with debugger that event handler is called) by changing the state of the input pin. I did test on a nRF52833 DK with emulation for nRF52820,as I do not have a board with the actual chip available right now.

If your logging stops, it sounds like a hardfault or similar have occurred. This may have happened if you have configured the project incorrectly, or with wrong MDK files. If you could upload the full project, I can have a look at it.

Best regards,
Jørgen

[Jørgen Holmefjord]

Since nRF52820 does not have a LPCOMP peripheral, there is no PRS box defined for sharing resources between COMP and LPCOMP. The interrupts from NVIC will be triggered directly in nrfx_comp_irq_handler (redefined from COMP_IRQHandler, which is the default handler name defined in the MDK files). In chips variants where both LPCOMP and COMP are available, and PRS is enabled, a common interrupt handler inside PRS is defined, where interrupts are forwarder instead of the default NRFX IRQ handler for that peripheral.

[logan.xu]

Thank you. As your suggestion, I mofify the define of nrfx_comp_irq_handler In nrfx_irqs_nrf52820.h, "#define COMP_LPCOMP_IRQHandler" to "#define COMP_IRQHandler", it works now. 

[logan.xu]

Hi，Jorgen,

        I have another question. I set the threhold param as follow:

        comp_config.threshold.th_down = NRFX_VOLTAGE_THRESHOLD_TO_INT(2.0, 3.3);
        comp_config.threshold.th_up = NRFX_VOLTAGE_THRESHOLD_TO_INT(2.8, 3.3);

        And if the VIN+ is 2.5V(above 2.0V) when call nrf_drv_comp_start(NRFX_COMP_EVT_EN_CROSS_MASK, 0), so the value of nrfx_comp_sample()  is 1. When VIN+ increase from 2.5V to 3.0V, it won't generate interrupt. It only generate when VIN+ decrease from 2.5V to 1.5V(for example). 

        I hope it can generate interrupt both when increase above 2.8V and decrease bellow 2.0V. Does it possible?

        

[Jørgen Holmefjord]

If you look at the description and figures in the COMP peripheral documentation, you will see that this is not possible. VIN- will initially be set to either VUP or VDOWN, depending on if VIN+ is ABOVE or BELOW VIN-. The VIN- needs to cross VIN+ in the given direction before it switch to detecting crossing in the other direction.

So after the input have increased to 3.0V, you should be able to detect the down crossing if decreasing the input to 1.5V again.