test.c

volatile int bufn,obufn;
uint16_t buf[5][128];
q15_t out[640];
q15_t outsq[1280];

void ADC_Handler(){
  int f=ADC->ADC_ISR;
  if (f&(1<<27)){
   bufn=(bufn+1);if(bufn==5)bufn=0;
   ADC->ADC_RNPR=(uint32_t)buf[bufn];
   ADC->ADC_RNCR=128;
  } 
}

void loop(){

  while(obufn==bufn);
  obufn=bufn;    

  int bb=bufn+1;if(bb==5)bb=0;
  uint16_t *q=buf[0]+128*bb;
  for(int j=0;j<512;j++){
    int t=(*q++)-2048;
    if(q==(buf[0]+640))q=buf[0];
    out[j]=t<<4;
  }
  
  // ...

}

I forgot if I linked to this from anywhere or if I can delete this.