Using timer to count pulse width on interrupt pin

RE: Using timer to count pulse width on interrupt pin

ovrebekk — Wed, 15 Feb 2023 09:11:24 GMT

Thanks a lot for sharing the solution, good to hear you were able to get it to work!

I will close the ticket then.

RE: Using timer to count pulse width on interrupt pin

Gabriel Pinto — Tue, 14 Feb 2023 17:05:29 GMT

Just to give some closure to ths thread, I did manage to implement this with a help of a colleague, but not following this method, as I couldn't figure out what was wrong.

What we did was use the timers with a resolution of 10us, to count each time there was an interrupt on the GPIOTE peripheral activated by a toggle of the pin, this proved to be enough as I didn't exactly need to know the time of pulse in the "high" state, but only the duration between the pin toggles. With a state machine I then managed to parse the durations in accordance to the protocol type I was expecting (NEC IR protocol).

Best regards, and thanks for the support.

RE: Using timer to count pulse width on interrupt pin

ovrebekk — Thu, 02 Feb 2023 11:43:46 GMT

I mean that you configure the GPIOTE by writing to the CONFIG registers directly, using hard coded indexes.

Something like this:

NRF_GPIOTE->CONFIG[0] = GPIOTE_CONFIG_MODE_Event << GPIOTE_CONFIG_MODE_Pos |
						GPIOTE_CONFIG_POLARITY_LoToHi << GPIOTE_CONFIG_POLARITY_Pos |
						IR_RECEIVER_PIN << GPIOTE_CONFIG_PSEL_Pos;
NRF_GPIOTE->CONFIG[1] = GPIOTE_CONFIG_MODE_Event << GPIOTE_CONFIG_MODE_Pos |
						GPIOTE_CONFIG_POLARITY_HiToLo << GPIOTE_CONFIG_POLARITY_Pos |
						IR_RECEIVER_PIN << GPIOTE_CONFIG_PSEL_Pos;

Best regards
Torbjørn

RE: Using timer to count pulse width on interrupt pin

Gabriel Pinto — Wed, 01 Feb 2023 17:13:37 GMT

Hi Torbjorn.

By hard coding, do you mean just assigning the PPI channel to the GPIOTE channel this way?

    nrfx_ppi_channel_alloc(&ppi_channel_a);
    nrfx_ppi_channel_assign(ppi_channel_a,(uint32_t)&NRF_GPIOTE->EVENTS_IN[0], nrfx_timer_task_address_get(&m_timer, NRF_TIMER_TASK_START));
    nrfx_ppi_channel_fork_assign(ppi_channel_a, nrfx_timer_task_address_get(&m_timer, NRF_TIMER_TASK_CLEAR));
    nrfx_ppi_channel_enable(ppi_channel_a);

    nrfx_ppi_channel_alloc(&ppi_channel_b);
    nrfx_ppi_channel_assign(ppi_channel_b,(uint32_t)&NRF_GPIOTE->EVENTS_IN[1], nrfx_timer_task_address_get(&m_timer, NRF_TIMER_TASK_STOP));
    nrfx_ppi_channel_fork_assign(ppi_channel_b, nrfx_timer_task_address_get(&m_timer, NRF_TIMER_TASK_CAPTURE0));
    nrfx_ppi_channel_enable(ppi_channel_b);

I'm assuming it starts by assigning channel 0, 1 and so on. However just by doing this I'm not getting any results inn my main loop.

Here's the full code on my main function:

    nrf_drv_gpiote_in_config_t in_config_1 = GPIOTE_CONFIG_IN_SENSE_LOTOHI(true);
    nrf_drv_gpiote_in_config_t in_config_2 = GPIOTE_CONFIG_IN_SENSE_HITOLO(true);
    nrfx_gpiote_in_init(IR_RECEIVER_PIN, &in_config_1, gpiote_handler);
    nrfx_gpiote_in_init(IR_RECEIVER_PIN, &in_config_2, gpiote_handler);
    nrf_drv_gpiote_in_event_enable(IR_RECEIVER_PIN, true);

    nrf_drv_timer_config_t timer_cfg = NRF_DRV_TIMER_DEFAULT_CONFIG;
    err_code = nrf_drv_timer_init(&m_timer, &timer_cfg, NULL);
    APP_ERROR_CHECK(err_code);
    nrf_drv_timer_enable(&m_timer);

    nrfx_ppi_channel_alloc(&ppi_channel_a);
    nrfx_ppi_channel_assign(ppi_channel_a,(uint32_t)&NRF_GPIOTE->EVENTS_IN[0], nrfx_timer_task_address_get(&m_timer, NRF_TIMER_TASK_START));
    nrfx_ppi_channel_fork_assign(ppi_channel_a, nrfx_timer_task_address_get(&m_timer, NRF_TIMER_TASK_CLEAR));
    nrfx_ppi_channel_enable(ppi_channel_a);

    nrfx_ppi_channel_alloc(&ppi_channel_b);
    nrfx_ppi_channel_assign(ppi_channel_b,(uint32_t)&NRF_GPIOTE->EVENTS_IN[1], nrfx_timer_task_address_get(&m_timer, NRF_TIMER_TASK_STOP));
    nrfx_ppi_channel_fork_assign(ppi_channel_b, nrfx_timer_task_address_get(&m_timer, NRF_TIMER_TASK_CAPTURE0));
    nrfx_ppi_channel_enable(ppi_channel_b);

    // Enter main loop.
    for (;;) {
      idle_state_handle();
      pulse_length = nrfx_timer_capture_get(&m_timer, NRF_TIMER_CC_CHANNEL0);
      NRF_LOG_INFO("PULSE LENGTH: %u",pulse_length);
      nrf_delay_ms(1000);
    }

To clarify the NRF_LOG_INFO just prints 0 on the pulse length.

Am I missing something?

Thank you and best regards

RE: Using timer to count pulse width on interrupt pin

ovrebekk — Fri, 27 Jan 2023 09:31:33 GMT

My bad, I didn't realize you were using the nRF5 SDK...

You can just hard code the channels. The GPIOTE peripheral has 8 channels in total, which means channel indexes in the range 0 to 7 are available.

It is just critical to ensure that if you have other parts of your application using the nrf_gpiote driver you don't get a conflict where you are trying to use the same GPIOTE channels multiple places.

Best regards
Torbjørn

RE: Using timer to count pulse width on interrupt pin

Gabriel Pinto — Thu, 26 Jan 2023 12:52:46 GMT

Hello Torbjorn.

I just checked the nrfx_gpiote drivers and the nrfx_gpiote_channel_alloc() function doesn't seem to exist, that's why I tried to translate the code Jared provided to my case.

According to those drivers the allocation is done automatically through the in_init function:

nrfx_err_t nrfx_gpiote_in_init(nrfx_gpiote_pin_t pin, nrfx_gpiote_in_config_t const * p_config, nrfx_gpiote_evt_handler_t evt_handler)

Of course this function assumes I have previously declared a config before as in:

nrf_drv_gpiote_in_config_t in_config_1 = GPIOTE_CONFIG_IN_SENSE_LOTOHI(true);

But through this method I'm not associating a channel to LoToHi and HiToLo events and this way I don't know how to assign the different PPI channels to each event.

Is there any other way to do this?

Thank you for your support.

Best regards.

RE: Using timer to count pulse width on interrupt pin

ovrebekk — Thu, 26 Jan 2023 12:05:32 GMT

Hi Gabriel

Jared is currently unavailable, and I will help you out in the mean time.

The nrfx_gpiote driver is a bit limited if you want to assign multiple GPIOTE channels to the same pin, since the pin is used to index the different channels rather than the channel index.

In this case I think you would have to use the nrfx_gpiote driver only for allocating the channels, using the nrfx_gpiote_channel_alloc(uint8_t * p_channel) function, and then configure the channels directly using the NRF_GPIOTE->CONFIG[ch] registers. Then you need to use the channel index provided by the alloc function as an index in the CONFIG register.

Small example:

#define IR_PIN 9
uint8_t gpiote_ch_a, gpiote_ch_b;
nrfx_gpiote_channel_alloc(&gpiote_ch_a);
nrfx_gpiote_channel_alloc(&gpiote_ch_b);
NRF_GPIOTE->CONFIG[gpiote_ch_a] = GPIOTE_CONFIG_MODE_Event << GPIOTE_CONFIG_MODE_Pos |
						GPIOTE_CONFIG_POLARITY_LoToHi << GPIOTE_CONFIG_POLARITY_Pos |
						IR_PIN << GPIOTE_CONFIG_PSEL_Pos;
NRF_GPIOTE->CONFIG[gpiote_ch_b] = GPIOTE_CONFIG_MODE_Event << GPIOTE_CONFIG_MODE_Pos |
						GPIOTE_CONFIG_POLARITY_HiToLo << GPIOTE_CONFIG_POLARITY_Pos |
						IR_PIN << GPIOTE_CONFIG_PSEL_Pos;

Best regards
Torbjørn

RE: Using timer to count pulse width on interrupt pin

Gabriel Pinto — Mon, 23 Jan 2023 17:41:44 GMT

Hi Jared, thanks for the example, I have a question though.

How do I assign the different ppi channels to the different gpiote configs? I have these two configs:

nrf_drv_gpiote_in_config_t in_config_1 = GPIOTE_CONFIG_IN_SENSE_LOTOHI(true);
nrf_drv_gpiote_in_config_t in_config_2 = GPIOTE_CONFIG_IN_SENSE_HITOLO(true);
nrfx_gpiote_in_init(IR_RECEIVER_PIN, &in_config_1, gpiote_handler);
nrfx_gpiote_in_init(IR_RECEIVER_PIN, &in_config_2, gpiote_handler);

But when I assign the ppi channels I'm doing the following:

    nrfx_ppi_channel_alloc(&ppi_channel_a);
    nrfx_ppi_channel_assign(ppi_channel_a, nrfx_gpiote_in_event_addr_get(IR_RECEIVER_PIN), nrfx_timer_task_address_get(&m_timer, NRF_TIMER_TASK_START));
    nrfx_ppi_channel_fork_assign(ppi_channel_a, nrfx_timer_task_address_get(&m_timer, NRF_TIMER_TASK_CLEAR));
    nrfx_ppi_channel_enable(ppi_channel_a);

    nrfx_ppi_channel_alloc(&ppi_channel_b);
    nrfx_ppi_channel_assign(ppi_channel_b, nrfx_gpiote_in_event_addr_get(IR_RECEIVER_PIN), nrfx_timer_task_address_get(&m_timer, NRF_TIMER_TASK_STOP));
    nrfx_ppi_channel_fork_assign(ppi_channel_b, nrfx_timer_task_address_get(&m_timer, NRF_TIMER_TASK_CAPTURE0));
    nrfx_ppi_channel_enable(ppi_channel_b);

However this doesn't seem to be assigning the PPI to LOTOHI and HITOLO events but rather any gpiote event. Am I missing something? Can I configure GPIOTE channels in a different way?

Thank you for your help.

RE: Using timer to count pulse width on interrupt pin

Jared — Wed, 18 Jan 2023 15:34:59 GMT

Hi,

I'm sorry for the late reply, I was looking for other threads that might had done the same and I see that I sent you the wrong one. I was supposed to send you this example that my colleague Torbjørn made for Zephyr. It should be a small task to port it to nRF5SDK. Come back to me if you're not able to port it and I'll do it... Either way this is the correct one.

regards

Jared

devzone.nordicsemi.com/.../5736.pulse_5F00_length_5F00_measurement.zip

RE: Using timer to count pulse width on interrupt pin

Gabriel Pinto — Fri, 13 Jan 2023 15:16:58 GMT

Hi Jared, Thank you for your answer.

I've been reading that thread before, but I always assumed that my application was supposed to be simpler.

Am I then to assume that measuring an IR signal requires either 2 simultaneous timers, or GPIOTE + TIMER + PPI? Or is this possible with only GPIOTE + TIMER like I'm doing?

Neither of the examples of your colleague Jorgen seems to directly correspond to my situation, which one should I follow?

RE: Using timer to count pulse width on interrupt pin

Jared — Fri, 13 Jan 2023 13:23:28 GMT

Hi,

My colleague Jørgen has already shared a project on how to implement this here. Could you take a look at it?

regards

Jared