Can't register more than two GPIOTE inputs

Question

Hello all, 
 I currently have a test rig with 3 sensors, each with their own pin and interrupt they are supposed to carry out. Whichever two I put first in my gpiote_init() function will always work and setup properly while the third throws a NRF_ERROR_NO_MEM error. Here's code. 
 (NOTE: The only other pins I have setup are two PWM output pins which both function fine.) 
 void gpiote_init()
{
//printf("Enter gpiote_init");

uint32_t err_code;
if(!nrf_drv_gpiote_is_init())
{
	err_code = nrf_drv_gpiote_init();
	if (err_code != NRF_SUCCESS)
	{
 //printf("Error init GPIOTE Module");
	}
	else
	{
 //printf("SUCCESS init GPIOTE Module");
	}
}

#define HOME_PIN 25
#define MASS_PIN 28
#define DOSE_PIN 30

//sensor pin interrupt setup
nrf_drv_gpiote_in_config_t config = GPIOTE_CONFIG_IN_SENSE_LOTOHI(true);

err_code = nrf_drv_gpiote_in_init(HOME_PIN, &config, sensor_home_interrupt);
if (err_code != NRF_SUCCESS)
{
	//printf("Error init sensor_home_interrupt");
}
nrf_drv_gpiote_in_event_enable(HOME_PIN, true);

err_code = nrf_drv_gpiote_in_init(MASS_PIN, &config, sensor_massage_interrupt);
if (err_code != NRF_SUCCESS)
{
	//printf("Error init sensor_massage_interrupt");
}
nrf_drv_gpiote_in_event_enable(MASS_PIN, true);

err_code = nrf_drv_gpiote_in_init(DOSE_PIN, &config, sensor_dose_interrupt);
if (err_code != NRF_SUCCESS)
{
	//printf("Error init sensor_dose_interrupt");
}
nrf_drv_gpiote_in_event_enable(DOSE_PIN, true);

NVIC_EnableIRQ(GPIOTE_IRQn);

return;
}
 
 As you can see all three of my declarations are straight up copies of the ones found in the infocenter, why I am only capped at two is beyond me. 
 For the PWM init I use the app_pwm, I don't believe I am using GPIOTE channels for them, though I may be wrong. Heres the pwm_init. 
 int pwm_init()
{
ret_code_t err_code0;
ret_code_t err_code1;

/* 1-channel PWM, 2000Hz, output to LED1 and LED2 */
//100 = 1kHz, 200 = .5 kHz
app_pwm_config_t pwm0_cfg = APP_PWM_DEFAULT_CONFIG_1CH(50L, BSP_LED_0);
app_pwm_config_t pwm1_cfg = APP_PWM_DEFAULT_CONFIG_1CH(50L, BSP_LED_1);

/* Active High */
pwm0_cfg.pin_polarity[0] = APP_PWM_POLARITY_ACTIVE_HIGH;
pwm1_cfg.pin_polarity[0] = APP_PWM_POLARITY_ACTIVE_HIGH;

/* Initialize and enable PWM. */
err_code0 = app_pwm_init(&PWM0,&pwm0_cfg,pwm_ready_callback);
err_code1 = app_pwm_init(&PWM1,&pwm1_cfg,pwm_ready_callback);
APP_ERROR_CHECK(err_code0);
APP_ERROR_CHECK(err_code1); 
	
return 0;
}

Ole Bauck · Accepted Answer

As said in the comment the nRF51 has only 4 GPIOTE channels used for output (OUT) or input (IN). The PWM library uses one per PWM channel, so you are trying to use 5 total (2 OUT and 3 IN). You can use PORT event instead for some pins by configuring it for "low accuracy" with 
 nrf_drv_gpiote_in_config_t config = GPIOTE_CONFIG_IN_SENSE_LOTOHI(false);
 
 PORT event is less accurate, but also uses less power and are only limited by the number of pins available (PORT event is shared between all pins set up for this).

Can't register more than two GPIOTE inputs

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