operate UART w/ NIOS wo/ HAL

Altera_Forum · ‎06-26-2016

The following code should make a loopback between UART RX and TX (echo).

However, it seems that first N typed chars (from PC towards the board) are not successfully absorbed.

After N characters (few dozens, I guess), it works correctly (I get an echo for each character I type).

Any ideas?

# include "altera_avalon_uart_regs.h"# include "system.h"
typedef unsigned char      u8;
typedef unsigned short     u16;
typedef unsigned int       u32;
# define UART_BASE        UART_0_BASE
int main ()
{
    u8  uart_rx_char;
    u16 uart_st_reg;
    while (1) {
        uart_st_reg = (u16)IORD_ALTERA_AVALON_UART_STATUS(UART_BASE);
        if (uart_st_reg & ALTERA_AVALON_UART_STATUS_RRDY_MSK) {
            uart_rx_char = (u8)IORD_ALTERA_AVALON_UART_RXDATA(UART_BASE);
            IOWR_ALTERA_AVALON_UART_TXDATA(UART_BASE, uart_rx_char);
        }
    }
    return 0;
}

Altera_Forum · ‎07-11-2016

Hi,

try to check if transmit is ready before you write in your txdata, and clear the status register in the begining of your while.