PPI and timers

RE: PPI and timers

ovrebekk — Wed, 01 Dec 2021 12:19:18 GMT

You can look at the implementation of counter_nrfx_timer.c for details.

If you look here you can see that CC register 0 is used to store the top value, and CC register 1 is used every time you want to read out the current state of the timer in the read() function.

The TIMER module does not allow you to read out the state of the timer without running a capture operation, and in order to do a capture you need to have a free CC register to store the capture value, which is why CC1 is assigned to this task only.

This leaves only two more free CC registers (CC2 and CC3) to store custom values, and the CC_TO_ID and ID_TO_CC macros are used to convert between CC number and channel ID.

Best regards
Torbjørn

RE: PPI and timers

creative.industry.ag — Tue, 30 Nov 2021 13:17:19 GMT

Yes, but why there is this offset?

RE: PPI and timers

ovrebekk — Tue, 30 Nov 2021 11:13:12 GMT

That makes sense. TIMER1 in the nRF52832 has 4 CC registers (CC0-CC3), so if CC2 is used for channel ID 0 and CC3 for channel ID 1, then there are only CC registers available for 2 channels.

If you want more direct control of the timer and its registers you can use the nrfx_timer library instead.

Best regards
Torbjørn

RE: PPI and timers

creative.industry.ag — Mon, 29 Nov 2021 14:42:27 GMT

uint32_t adr = counter_get_num_of_channels(timer_dev);

adr = 0x02

RE: PPI and timers

ovrebekk — Fri, 26 Nov 2021 07:32:43 GMT

What do you get if you run the counter_get_num_of_channels(..) function?

It is not necessarily a direct mapping between the counter channel ID and the CC register value. The counter driver is probably using some CC registers for other purposes, so that it is not able to use all of them for registering alarms.

Best regards
Torbjørn

RE: PPI and timers

creative.industry.ag — Thu, 25 Nov 2021 05:59:03 GMT

I believe i found problem in driver, but i may be wrong.

My code:

#include <zephyr.h>
#include <debug/ppi_trace.h>
#include <drivers/counter.h>
#include <hal/nrf_rtc.h>
#include <hal/nrf_clock.h>
#include <hal/nrf_timer.h>
#include <nrfx_timer.h>
#include <device.h>
#include <logging/log.h>

LOG_MODULE_REGISTER(app);
#define ALARM_PERIOD_US 1000 * 1000
#define TIMER NRF_TIMER1
#define TIMER_LABEL DT_LABEL(DT_NODELABEL(timer1))

static void timer_callback(const struct device *dev, uint8_t chan_id, uint32_t ticks,
						   void *user_data);

static struct counter_alarm_cfg TIM0_alarm_cfg = {
	.callback = timer_callback,
	.flags = 0, //?
};

static void ppi_trace_pin_setup(uint32_t pin, uint32_t evt)
{
	void *handle;

	handle = ppi_trace_config(pin, evt);
	__ASSERT(handle != NULL,
			 "Failed to initialize trace pin, no PPI or GPIOTE resources?");

	ppi_trace_enable(handle);
}

static void ppi_trace_setup(void)
{
	ppi_trace_pin_setup(19, nrf_timer_event_address_get(TIMER, NRF_TIMER_EVENT_COMPARE0));

	ppi_trace_pin_setup(20, nrf_timer_event_address_get(TIMER, NRF_TIMER_EVENT_COMPARE2));

	LOG_INF("PPI trace setup done.");
}

static void timer_callback(const struct device *dev, uint8_t chan_id,
						   uint32_t ticks, void *user_data)
{
	int err;
	uint32_t alarm_cnt = (uint32_t)user_data + 1;

	TIM0_alarm_cfg.ticks = counter_us_to_ticks(dev, ALARM_PERIOD_US );
	TIM0_alarm_cfg.user_data = (void *)alarm_cnt;
	LOG_INF("timer_callback %d ", TIM0_alarm_cfg.ticks);
	err = counter_set_channel_alarm(dev, 0, &TIM0_alarm_cfg);
	__ASSERT_NO_MSG(err == 0);
	(void)err;
}

static void counter_setup(void)
{
	int err;
	const struct device *dev = device_get_binding(TIMER_LABEL);

	__ASSERT(dev, "Sample cannot run on this board.");

	TIM0_alarm_cfg.ticks = counter_us_to_ticks(dev, ALARM_PERIOD_US);

	err = counter_set_channel_alarm(dev, 0, &TIM0_alarm_cfg);
	__ASSERT_NO_MSG(err == 0);

	err = counter_start(dev);
	__ASSERT_NO_MSG(err == 0);
}

void main(void)
{
	ppi_trace_setup();
	counter_setup();

	while (1)
	{
		k_msleep(1000);
	}
}

Description:

I working on nrf52832 dk.

The problem is with the wrong selection of the timer alarm channel. I call function which should use channel 0 timer 1

counter_set_channel_alarm(dev_tim, NRF_TIMER_CC_CHANNEL0, &TIM0_alarm_cfg);

But the driver has assigned an alarm interrupt on channel 2, you can see it in the CPU registers. ( active interrupt 2 not 0)

RE: PPI and timers

ovrebekk — Wed, 24 Nov 2021 14:05:15 GMT

You mean to say you found the problem in your own code, or that there is a bug in the one of the drivers?

Best regards
Torbjørn

RE: PPI and timers

creative.industry.ag — Wed, 24 Nov 2021 09:55:26 GMT

I managed to run ppi on a fast timer, it turned out that the "counter_set_channel_alarm" function that was supposed to set an alarm on channel 0 sets it on channel 2.