Processor-FPGA Communication: Using FIFO Processor Part

Date:

20 Sep 2019

What are we gonna do?

• We will write a simple counter in the FPGA Part, the counter increases \(1\) every clk cycle

• This counter makes a write request every \(2^{24}\) clk cycle to the FIFO, and writes the counter value to the FIFO

• To FIFO read port is connected to 3 PIOs generated by Platform Designer(Qsys), these 3 PIOs can be directly accessed by the Processor via memory mapping, since this memory is shared by the FPGA and Processor

• Meanwhile, the 8 LEDs on the DE10-NANO board are connected to usedw (used words) which indicates the number of data stored in the FIFO

• We will write a simple reader in the Processor Part

• User execute the compiled C code in the terminal, then they type in number of data to read

• They will see read data printed to the terminal, as well as the decrease in number indicated by the LED

Modify the Standard Example HPS_FPGA_LED/main.c

• Recall the address map earlier

• Use it

// FIFO
h2p_lw_FIFOreadRequest_addr = virtual_base + (
                (unsigned long)(ALT_LWFPGASLVS_OFST + 0x40000) &
                (unsigned long)(HW_REGS_MASK)
        );
h2p_lw_FIFOreadDataQueue_addr = virtual_base + (
                (unsigned long)(ALT_LWFPGASLVS_OFST + 0x40010) &
                (unsigned long)(HW_REGS_MASK)
        );
h2p_lw_FIFOreadEmpty_addr = virtual_base + (
                (unsigned long)(ALT_LWFPGASLVS_OFST + 0x40020) &
                (unsigned long)(HW_REGS_MASK)
        );

• Handle FIFO reading

int FIFOread(){
        if(*(uint32_t *)h2p_lw_FIFOreadEmpty_addr != 1){
                *(uint32_t *)h2p_lw_FIFOreadRequest_addr = 1;
                usleep(1);
                *(uint32_t *)h2p_lw_FIFOreadRequest_addr = 0;
                return(0); // successful
        }
        return(1); // failed due to empty
}

The full code

#include <string.h>
#include <inttypes.h>

#include <stdio.h>
#include <unistd.h> // provides access to the POSIX operating system API
#include <fcntl.h>  // header in the C POSIX library
#include <sys/mman.h> // memory management
#include "hwlib.h" // location: SoC EDS\embedded\ip\altera\hps\altera_hps\hwlib\include
#include "socal/socal.h" // location: SoC EDS\embedded\ip\altera\hps\altera_hps\hwlib\include\soc_cv_av\socal
#include "socal/hps.h"
#include "socal/alt_gpio.h"

#include "hps_0.h" //

#define HW_REGS_BASE ( ALT_STM_OFST )
#define HW_REGS_SPAN ( 0x04000000 )
#define HW_REGS_MASK ( HW_REGS_SPAN - 1 )

//////////////////////////////////////////////////

void *virtual_base;
void *h2p_lw_led_addr;

// FIFO
void *h2p_lw_FIFOreadRequest_addr;
void *h2p_lw_FIFOreadDataQueue_addr;
void *h2p_lw_FIFOreadEmpty_addr;

int fd;

//////////////////////////////////////////////////

int memoryMapping(){
        // Map the **Address Space** for LED registers
        // into **User Space** so we can use them
        // We'll actually map in the entire CSR ??? span of
        // the HPS since we want to access various registers
        // within that span.

        fd = open("/dev/mem", ( O_RDWR | O_SYNC ) );
        if( fd == -1 ){
                printf("Error: can't open \"/dev/mem\" \n");
                return(1);
        }

        virtual_base = mmap(NULL, HW_REGS_SPAN, (PROT_READ|PROT_WRITE),
                MAP_SHARED, fd, HW_REGS_BASE);

        if(virtual_base == MAP_FAILED){
                printf("Error: mmap() failed \n");
                close(fd);
                return(1);
        }

        h2p_lw_led_addr = virtual_base + (
                        (unsigned long)(ALT_LWFPGASLVS_OFST + LED_PIO_BASE) &
                        (unsigned long)(HW_REGS_MASK)
                );

        // FIFO
        h2p_lw_FIFOreadRequest_addr = virtual_base + (
                        (unsigned long)(ALT_LWFPGASLVS_OFST + 0x40000) &
                        (unsigned long)(HW_REGS_MASK)
                );
        h2p_lw_FIFOreadDataQueue_addr = virtual_base + (
                        (unsigned long)(ALT_LWFPGASLVS_OFST + 0x40010) &
                        (unsigned long)(HW_REGS_MASK)
                );
        h2p_lw_FIFOreadEmpty_addr = virtual_base + (
                        (unsigned long)(ALT_LWFPGASLVS_OFST + 0x40020) &
                        (unsigned long)(HW_REGS_MASK)
                );

        return(0);
}

int FIFOread(){
        if(*(uint32_t *)h2p_lw_FIFOreadEmpty_addr != 1){
                *(uint32_t *)h2p_lw_FIFOreadRequest_addr = 1;
                usleep(1);
                *(uint32_t *)h2p_lw_FIFOreadRequest_addr = 0;
                return(0); // successful
        }
        return(1); // failed due to empty
}

int FIFOreadContinuously(){
        int i;
        int n;
        while(1){
                printf( "Number of words to read: ");
                scanf("%d", &i);
                for (n=0;n<i;n++){
                        if(FIFOread()==0){
                                printf( "Value: ");
                        printf("%" PRIu32 "\n",*(uint32_t *)h2p_lw_FIFOreadDataQueue_addr);
                                printf( "\n");
                        }
                        else{
                                printf( "Empty!\n");
                        }
                }
        }
        return(0);
}

int cleanMemoryAndExit(){
        if( munmap(virtual_base,HW_REGS_SPAN)!=0 ){
                printf("Error: munmap() failed \n");
                close(fd);
                return(1);
        }
        close(fd);
        return(0);
}

/////////////////////////////////////////////////////

int main(){
        memoryMapping();
        FIFOreadContinuously();
        cleanMemoryAndExit();
        return(0);
}