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HPS Avalon MM FIFO dump data at read status pointer 0

output.JPGfifo settings.JPG​Hi, I have following questions?

  1. Why read pointer is 1 less than the write pointer?
  2. What is this dump value 19844532 at position 0 of read status pointer?
  3. I am writing 1 to 8 to fifo but not getting the last digits as fifo read status pointer reaches 0.

Here is my code and designs.

#include <stdio.h> #include <unistd.h> #include <stdlib.h> #include <stdint.h> #include <fcntl.h> #include <sys/mman.h> #include <sys/types.h> #include <sys/stat.h> #include "C:\altera\15.1\embedded\ip\altera\hps\altera_hps\hwlib\include\hwlib.h" #include "C:\altera\15.1\embedded\ip\altera\hps\altera_hps\hwlib\include\soc_cv_av\socal\socal.h" #include "C:\altera\15.1\embedded\ip\altera\hps\altera_hps\hwlib\include\soc_cv_av\socal\hps.h" #include "C:\altera\15.1\embedded\ip\altera\hps\altera_hps\hwlib\include\soc_cv_av\socal\alt_gpio.h" #include "D:\TestDesigns\customfifoloopback1\hps_0.h" //fifo status pointers //#define FIFO_FULL ((*(FIFO_write_status_ptr+1))& 1 ) //#define FIFO_EMPTY ((*(FIFO_read_ptr+1))& 2 ) //LW Addresses #define REG_BASE 0xFF200000 #define REG_SPAN 0x00200000 //initializing the pointers void* virtual_base; volatile unsigned int * FIFO_write_status_ptr= NULL; volatile unsigned int * FIFO_read_status_ptr = NULL ; volatile unsigned int * FIFO_write_ptr = NULL ; volatile unsigned int * FIFO_read_ptr = NULL ; unsigned int value; int data[5]; int i; //int FIFO_FULL; //int FIFO_EMPTY; //main functions int main () { int fd = EXIT_FAILURE; fd=open("/dev/mem",(O_RDWR|O_SYNC)); if (fd < 0) { perror("open"); exit(EXIT_FAILURE); } printf("fd is ok\n"); //accessing the virtual addresses of the fifo pointers virtual_base=mmap(NULL,REG_SPAN,(PROT_READ|PROT_WRITE),MAP_SHARED,fd,REG_BASE); printf("virtual base pointer to open device memory file is ok\n"); FIFO_write_status_ptr = (unsigned int *)(virtual_base+FIFO_0_IN_CSR_BASE); FIFO_read_status_ptr = (unsigned int *)(virtual_base+FIFO_0_OUT_CSR_BASE); FIFO_write_ptr=(unsigned int *)(virtual_base+FIFO_0_IN_BASE); FIFO_read_ptr= (unsigned int *)(virtual_base+FIFO_0_OUT_BASE); printf("fifo pointers are ok\n"); //entering data into the fifo for(i=0;i<8;i++) { data[i]=i+1; *FIFO_write_ptr=data[i]; printf("////////////////////////////\n"); printf("you entered the value %d\n",*FIFO_write_ptr); printf("fifo write status pointer is %d\n",*FIFO_write_status_ptr); printf("//////////////////////////////\n"); } printf("reading back the data\n"); for(i=0;i<8;i++) { //reading data from the fifo printf("////////////////////////////\n"); printf("the output value from the fifo is%d\n",*FIFO_read_ptr); printf("fifo read status pointer is %d\n",*FIFO_read_status_ptr); printf("/////////////////////////////\n"); } return 0; }


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May I know which Quartus Version you are using and are you using Cyclone V soc?