Little help with DMA reading from a source

Altera_Forum · ‎01-10-2011

Hello i have a fifo that get's filled after 10 seconds and i want to read half of the fifo from my DMA. How can i do that?

I am recieving a half_full signal from my fifo, which generates an IRQ.

I am getting this IRQ without any problem but i want to know how to tell the DMA to read 32 positions of my fifo (half).

My DMA CODE that works from SDRAM to ONCHIP ram is the follow

#include <stdio.h># include <unistd.h> // usleep()# include "system.h"# include "sys/alt_irq.h"# include "altera_avalon_pio_regs.h"# include <stdlib.h># include <stddef.h># include <string.h># include <io.h># include <alt_types.h># include "sys/alt_dma.h"# include "sys/alt_cache.h"# include "sys/alt_alarm.h"# include "sys/alt_irq.h"# include "alt_types.h"# include "altera_avalon_pio_regs.h"
static volatile int txrx_done = 0;
int i;
static void handle_button_interrupts(void* context, alt_u32 id);
volatile alt_u8 led=0;
/* A variable to hold the value of the button pio edge capture register. */
volatile int edge_capture;
volatile int irq_count;
//callback function when DMA transfer done
static void txrxDone(void * handle, void * data)
{
    txrx_done = 1;
}
void initMEM(int base_addr,int len)
{
    for ( i=0;i<len;i++)
    {
        IOWR_8DIRECT(base_addr,i,i);
    }
}
int initdma(void)
{
    printf("testing fifo & onchip : dma operation\n");
    alt_16 buffer;
    //memset((void *)SSRAM_0_BASE,0x7a,0x10);//this write base on byte
    //initMEM(FIFO_0_BASE,0x10);
    memset((void *)(DESTINO_BASE),0x33,0x10);
    printf("content of fifo:before DMA operation\n");
    for ( i=0;i<0x10;i++)
    {
        printf("%d: %x\n",i,IORD_8DIRECT(FIFOWRAPPER_0_BASE,i));
    }
    printf("content of onchip:before DMA operation\n");
    for ( i=0;i<0x10;i++)
    {
        printf("%d: %x\n",i,IORD_8DIRECT(DESTINO_BASE,i));
    }
    int rc;    //request
    alt_dma_txchan txchan;
    alt_dma_rxchan rxchan;
    void* tx_data = (void*)FIFOWRAPPER_0_BASE; /* pointer to data to send */
    void* rx_buffer = (void*)(DESTINO_BASE); /* pointer to rx buffer */
    /* Create the transmit channel */
    if ((txchan = alt_dma_txchan_open("/dev/dma_0")) == NULL)
    {
        printf ("Failed to open transmit channel\n");
        exit (1);
    }
    /* Create the receive channel */
    if ((rxchan = alt_dma_rxchan_open("/dev/dma_0")) == NULL)
    {
        printf ("Failed to open receive channel\n");
        exit (1);
    }
    /* Post the transmit request */
    if ((rc = alt_dma_txchan_send (txchan,
            tx_data,
            0x10,
            NULL,
            NULL)) < 0)
    {
        printf ("Failed to post transmit request, reason = %i\n", rc);
        //exit (1);
    }
    /* Post the receive request */
    if ((rc = alt_dma_rxchan_prepare (rxchan,
            rx_buffer,
            0x10,
            txrxDone,
            NULL)) < 0)
    {
        printf ("Failed to post read request, reason = %i\n", rc);
        //exit (1);
    }
    /* wait for transfer to complete */
    while (!txrx_done);
    printf ("Transfer successful!\n");
    printf("content of fifo:after DMA operation\n");
    for ( i=0;i<0x10;i++)
    {
        printf("%d: %x\n",i,IORD_8DIRECT(FIFOWRAPPER_0_BASE,i));
    }
    printf("content of onchip:after DMA operation\n");
    for ( i=0;i<0x10;i++)
    {
        printf("%d: %x\n",i,IORD_8DIRECT(DESTINO_BASE,i));
    }
    return 0;
}

Altera_Forum · ‎01-11-2011

Simply change to 32 the DMA length (which is now 0x10 in your example)

Then, you probably want the tx channel to get data from a constant address, since usually FIFOs work this way;

so, you need to set the RCON bit in the DMA control register (this applies to the standard Altera DMA core; in other cores there will be a similar control bit).

Altera_Forum · ‎01-11-2011

Hello Cris72, i see that the rcon bit is the bit number 8, what would be the C code to set it? I can't find in the literature..

Thanks

nvm you've answered me this before

#include "altera_avalon_dma_regs.h"
int reg;
reg = IORD_ALTERA_AVALON_DMA_CONTROL (dma_base_address);
IOWR_ALTERA_AVALON_DMA_CONTROL (dma_base_address, reg | ALTERA_AVALON_DMA_CONTROL_RCON_MSK);