Timer/Counter configuration issues

[exgreyfox]

Hello, 

I am having an issue with setting up the event generation timing on the nRF51822. Long story short, I am configuring Timer/Counter 0 to generate an event every 50ms. I am using this to generate an emergency kick-out during data exchange between an external uController and the nRF51822. I am seeing the timer/counter generate an event every 4ms instead. 

Now for a little background on my implementation. I am using the nRF51 development kit fly-wired to my external uController. I am building on the example implementation called ble_app_uart_pca10028_s130 using the s130 Bluetooth stack. This example did not have any of the 4 timer/counters enabled and implemented so to do so I referenced the timer_pca10028 example. I initialized timer/counter 0 in the following way:

const nrf_drv_timer_t TIMER = NRF_DRV_TIMER_INSTANCE(0);
volatile uint16_t EmergencyKickOut; // Used an infinite loop bailout or a time delay

/**@brief Application main function.
 */
int main(void)
{
    uint32_t err_code;
    bool erase_bonds;
	
    uint32_t time_ms = 50; //Time(in miliseconds) between consecutive compare events.
    uint32_t time_ticks;
	
    /* Set up the P0.04 MP_INT as an input ready to receive data wakeup pin */ 
    nrf_gpio_cfg_input(MP_INT, NRF_GPIO_PIN_NOPULL);

    /* Set up P0.05 BT_INT pin as MP wakeup pin */
    nrf_gpio_cfg_output( BT_INT );
    nrf_gpio_pin_write( BT_INT, PIN_LEVEL_LOW );
	
	/* Set up P0.06 DEBUG_PIN_06 pin as debug pin */
    nrf_gpio_cfg_output( DEBUG_PIN_06 );
    nrf_gpio_pin_write( DEBUG_PIN_06, PIN_LEVEL_LOW );
	      
    // Initialize.
    APP_TIMER_INIT(APP_TIMER_PRESCALER, APP_TIMER_OP_QUEUE_SIZE, false);
    uart_init();

    buttons_leds_init(&erase_bonds);
    ble_stack_init();
    gap_params_init();
    services_init();
    advertising_init();
    conn_params_init();
		
    //printf("\r\nUART Start!\r\n");
    err_code = ble_advertising_start(BLE_ADV_MODE_FAST);
    APP_ERROR_CHECK(err_code);
		
    // Configure TIMER_COUNTER_1 
    nrf_drv_timer_config_t timer_cfg = NRF_DRV_TIMER_DEFAULT_CONFIG;
    err_code = nrf_drv_timer_init(&TIMER, &timer_cfg, timer_event_handler);
    APP_ERROR_CHECK(err_code);
		
	time_ticks = nrf_drv_timer_ms_to_ticks(&TIMER, time_ms);
    nrf_drv_timer_extended_compare(&TIMER, NRF_TIMER_CC_CHANNEL0, time_ticks, NRF_TIMER_SHORT_COMPARE1_CLEAR_MASK, true);
		
	nrf_drv_timer_enable(&TIMER); 

    // Enter main loop.
    for (;;)
    {
        power_manage();
    }
}

/**
 * @brief Handler for timer events.
 */
void timer_event_handler(nrf_timer_event_t event_type, void* p_context)
{
    nrf_gpio_pin_toggle( DEBUG_PIN_06 ); // debugging trace
	if ( EmergencyKickOut )
	{
		EmergencyKickOut--;
	}
}

I have the following parameters that relate to Timer/counter configured in sdk_config.h as follows:

// <e> TIMER_ENABLED - nrf_drv_timer - TIMER periperal driver
//==========================================================
#ifndef TIMER_ENABLED
#define TIMER_ENABLED 1
#endif
#if  TIMER_ENABLED
// <o> TIMER_DEFAULT_CONFIG_FREQUENCY  - Timer frequency if in Timer mode
 
// <0=> 16 MHz 
// <1=> 8 MHz 
// <2=> 4 MHz 
// <3=> 2 MHz 
// <4=> 1 MHz 
// <5=> 500 kHz 
// <6=> 250 kHz 
// <7=> 125 kHz 
// <8=> 62.5 kHz 
// <9=> 31.25 kHz 

#ifndef TIMER_DEFAULT_CONFIG_FREQUENCY
#define TIMER_DEFAULT_CONFIG_FREQUENCY 0
#endif

// <o> TIMER_DEFAULT_CONFIG_MODE  - Timer mode or operation
 
// <0=> Timer 
// <1=> Counter 

#ifndef TIMER_DEFAULT_CONFIG_MODE
#define TIMER_DEFAULT_CONFIG_MODE 0
#endif

// <o> TIMER_DEFAULT_CONFIG_BIT_WIDTH  - Timer counter bit width
 
// <0=> 16 bit 
// <1=> 8 bit 
// <2=> 24 bit 
// <3=> 32 bit 

#ifndef TIMER_DEFAULT_CONFIG_BIT_WIDTH
#define TIMER_DEFAULT_CONFIG_BIT_WIDTH 3
#endif

// <o> TIMER_DEFAULT_CONFIG_IRQ_PRIORITY  - Interrupt priority
 

// <i> Priorities 0,2 (nRF51) and 0,1,4,5 (nRF52) are reserved for SoftDevice
// <0=> 0 (highest) 
// <1=> 1 
// <2=> 2 
// <3=> 3 

#ifndef TIMER_DEFAULT_CONFIG_IRQ_PRIORITY
#define TIMER_DEFAULT_CONFIG_IRQ_PRIORITY 1
#endif

// <q> TIMER0_ENABLED  - Enable TIMER0 instance
 

#ifndef TIMER0_ENABLED
#define TIMER0_ENABLED 1
#endif

I notice immediately upon flashing the nRF51 dev kit that it completely stops broadcasting Bluetooth. I have not taken time to debug exactly what occurs at this point but it seems that the application code in the nRF51822 has completely cratered at this point. Upon tinkering, I changed the implementation from using Timer/counter 0 to 1 and as soon as I did, it boot up and began executing as expected. The event generation works and I am able to use it as means to generate bailouts during inter-processor communication. 

I am configuring the Timer/counter to generate events at a 50ms rate however my debugging trace on pin P0.06 tells me that it is instead banging away at 4ms instead. I am assuming that I am having some sort of cross peripheral conflict here. To be blunt, I am still very new to the nRF line and still learning as I go so some insight on how to properly configure these peripherals to be congruent with the intended output would be greatly appreciated. 

[tommy.lane]

It sounds like the SoftDevice is using timer0, try initializing your interrupt to use timer1 instead.

[exgreyfox]

Does my configuration not do just that?

const nrf_drv_timer_t TIMER = NRF_DRV_TIMER_INSTANCE(0);
err_code = nrf_drv_timer_init(&TIMER, &timer_cfg, timer_event_handler);

[exgreyfox]

haakonsh any chance you might be able to point me to the prescalar definition?

[haakonsh]

See Chapter 18 of the nRF51 Reference Manual v3.0.1. 

I see now that the value TIMER_DEFAULT_CONFIG_FREQUENCY is actually the value of the PRESCALER register and should yield a 16MHz timer in your application. 

I need you to read out the value of the CC[0] register when the timer is running to verify that it is correctly set to 800 000dec. 

EDIT:

Are you using the SoftDevice? If so then you cannot use TIMER0 as it is used by the SoftDevice, see System on Chip resource requirements: Hardware peripherals.

[exgreyfox]

Yes I am using SoftDevice. I have made sure to switch to Timer 1 per your earlier instructions. I will get the value of CC[0] and get back to you. 

[exgreyfox]

haakonsh I just took a look at the value of register CC[0] and as I stepped through the code while debugging, after executing the line

nrf_drv_timer_extended_compare(&TIMER, NRF_TIMER_CC_CHANNEL0, time_ticks, NRF_TIMER_SHORT_COMPARE1_CLEAR_MASK, true);

CC[0] appears to contain the value 0x00003500 which is 13,568 dec. So I guess this is the discrepancy that we are seeing here. I see that time_ticks equates to 800,000 and is being passed as the cc_value argument to be written to register CC[0]. 800,000 dec = 0xC3500 in hex and what is actually making it into CC[0] is 0x3500. Somehow the 0xC0000 is being dropped. I tried simply forcing the value of CC[0] with the following code:

NRF_TIMER_Type * p_reg;
p_reg->CC[0] = 0xC3500;
nrf_drv_timer_enable(&TIMER); 

But I end up in the Hard fault Handler. 

Any ideas?

[haakonsh]

Yeah, I think the timer is configured for 16-bit only. What's the value of the BITMODE register?

[exgreyfox]

haakonsh BITMODE register is set to 32-bits. Are there any other registers you would like me to verify? This is very puzzling, I don't understand why this isn't working. All of the configurations look properly set.