Interrupts for Data Ready pin

Question

I have an external signal coming in from a device (AFE - Analog Front End) which I need to use as an interrupt to perform a task. The signal is active low, and it goes low whenever data is ready to be read from the device. It goes high ODR times (where ODR is the output data rate) in a second. I need to use it as a logic 0 level interrupt, reading data from the device using my K53 Kinetis microcontroller from Freescale. I am communicating via SPI with the microcontroller as master and AFE as slave

The issue is, only when I send NOPs to the AFE do I get data from the device, due to the two way nature of SPI. So unless I send NOP commands, I do not get the DRDY (data ready) signal from the AFE, which I must use as the interrupt - but, the DRDY signal tells me when I read data from the device (Giving NOP = giving clock cycles in which to receive data from the AFE. Thus, reading data = giving NOP commands).

So far, what I've done is given a few NOPs just after configuring the device to output data and enabling the interrupt - so that some data can come in and th eDRDY signal can come in. Without the NOPs, the DRDY signal is always low and I am stuck forever in the ISR. With the few NOPs before the main while, DRDY is generated, and within the ISR, I give more NOPs so that the DRDY signal can be sustained.

However, using the same code, it works sometimes, but sometimes it still gets stuck in the ISR. It is inconsistent, making me think that there are some serious timing issues here.

My code looks like this:

enable_irq(91);  
//this tells the device to output frames of data at ODR
reg_read_adas1000(0x40000000); 

for (i=0;i<1000;i++) 
//few NOPs - the slave in line is 0 
reg_read_adas1000(0x00000000); 

while (j<9900){
  asm("nop");
  j++; 
}

The ISR :

void porte_isr(void) {
  //giving NOP and storing data obtained from device in an array
  data_adas1000[inter_iter_flag]=reg_read_adas1000(0x00000000);        

  //increment counter
  inter_iter_flag++;

  //break out of the program at a suitable length of array
  if (inter_iter_flag >= 9900)
    disable_irq(91); 
  PORTE_ISFR = 0xFFFFFFFF; //Clear Flags  
}

Would really appreciate any help.