Uart loopback

I think a good place to start is to first make sure you can transmit a character and see it on an oscilloscope. Start out by bringing this pin to an output line and looking at it with an oscilloscope. You could also do this with Signaltap, but you may need to create a very deep memory b/c the serial transmission will likely be long relative to the clock frequency. My memory is that the UART tx line should be resting at a '1' normally, then toggling low during character times.

#include <stdio.h># include <unistd.h># include <stdint.h># include <fcntl.h># include "sys/alt_stdio.h"# include "system.h"# include "altera_avalon_uart_regs.h"# include "altera_avalon_uart.h"
int main()
{
    uint8_t tx_var=0xFF;
    uint8_t rrdy=0x00;
    uint8_t trdy=0x00;
    uint8_t tmt=0x00;
    uint16_t status=0x00;
    uint8_t rx_var=0x00;
    //write the byte to be sent
    printf("Scrivo il byte da trasmettere.\n");
    IOWR_ALTERA_AVALON_UART_TXDATA(UART_0_BASE, tx_var);
    status=IORD_ALTERA_AVALON_UART_STATUS(UART_0_BASE);
    tmt=(status & ALTERA_AVALON_UART_STATUS_TMT_MSK)>>5;
    while(tmt != 1){ //Untill the byte is not trasmitted
        status=IORD_ALTERA_AVALON_UART_STATUS(UART_0_BASE);
        tmt=(status & ALTERA_AVALON_UART_STATUS_TMT_MSK)>>5;
    }
    rrdy=(status & ALTERA_AVALON_UART_STATUS_RRDY_MSK ) >> ALTERA_AVALON_UART_STATUS_RRDY_OFST;
    while(rrdy !=1){//until the byte is not received
        rrdy=(status & ALTERA_AVALON_UART_STATUS_RRDY_MSK ) >> ALTERA_AVALON_UART_STATUS_RRDY_OFST;
        printf("status RRDY bit= %x\n", rrdy);
    };
    rx_var = IORD_ALTERA_AVALON_UART_RXDATA(UART_0_BASE);
    printf("rx_data= %x\n\n", rx_var);
return 0;
}

Thank you for your reply !! I have tried with a multimeter and I put the write comman in a loop. What I see is that the pin is always at 0 V.

A few possibilities:

1. If you are using an RS232 converter, it probably can't operate above a few hundred KHz. Make sure you're looking at the input to the RS232 converter.

2. Go into the assignment tool and verify that the txd_uart signal (or the clock signal) is routed to the correct FPGA pin.

3. Possibly check other pin assignments as well.

4. Check to make sure you have a clock!

5. Search and make sure that the txd_uart signal isn't routed to multiple places (some languages allow this).

6. Check to see if the FPGA really loaded?

SOLVED !